GB2507075A - Motor powered upwelling apparatus to generate food and fuel with carbon sequestration - Google Patents

Abstract

A tug boat 1 tows an inverted hydrofoil 15 at 60m depth in the North Sea with an intermediately positioned cable float 10 added to prevent wave action acting on the tug boat from being transmitted to the hydrofoil. Nutrient carrying seawater is propelled up to the photic zone such that Phytoplankton proliferate, so boosting fish stocks now in decline. The cable float when fully submerged is able to support the downforce applied by the hydrofoil to maintain an obtuse angle between a towing cable 7 connecting the tug boat to the cable float and a main cable 13 connecting the cable float to the hydrofoil. Less than 2 percent of energy yielded as biomass is needed to power the tug. Floating varieties of seaweed that reproduce by vegetative means can be converted to fuels with the crop confined by natural currents so access by shipping is not restricted.

Description

IMPROVEMENTS TO MOTOR POWERED UPWELLING APPARATUS FOR

OCEAN CULTIVATION TO GENERATE FOOD AND FUEL WITH CARBON

SEQUESTRATION

We Andrew. S. Wyon F,I.Mech.E. and Ronald Denzil Pearson(B.Sc.Eng) hereby apply for a patent that we hope will be granted.

This invention is an ocean cultivator that operates by having a hydrofoil towed at a depth to throw up seawater containing nutrients in such concentration as to promote the growth of marine algae such as the single celled phytoplankton. These form the base of the food web supporting harvestaHe fish. Since over fishing is causing serious decline of stocks a first aim of the invention is to boost fish stocks to alTest the decline. Sequestration of carbon absorbed from the atmosphere will also result to form a second objective. According to a careful technical assessment and economic analysis we show that the carbon credits for which the operation would be eligible could more than finance operation.

A long term objective is to provide sustainable energy from floating seaweed.

This short summary is provided since towed hydrofoils are described in the prior art and it is necessary to show why this does not anticipate the invention. Prior art has towed hydrofoils for producing a down force on their towing cables but these have totally different purposes from the present invention. The prior art describes such devices used simply to enable lines towing instruments or fishing apparatus to reach adequate depths. These are of very small scale as compared to the hydrofoils needed for ocean cultivation. The invention utilises hydrofoils comparable in size to the tug towing them to project a plume of nutrient calTying seawater to the photic zone to enable marine plants to proliferate.

The new invention is an improvement on that described in: MOTOR POWERED

UPWELLING APPARATUS FOR OCEAN CULTIVATION TO GENERATE FOOD

AND FUEL WITH CARBON SEQUESTRATION

Patent Application Number GBl2lOO97.0 ref: RDPOSO6I2 filed 08/6/12 The main claim of the above patent application is that the plan area of the hydrofoil exceeds the underwater frontal area of the tug used for towing. Such a hydrofoil is called an uppingvane.

Excessive fishing in the North Sea is endangenng many species and some could be rendered extinct unless preventive measures are implemented very soon. The marine food web depends on the unicellular algae called phytoplankton and the latter require adequate provision of inorganic nutrients such as inorganic carbon phosphates nitrates and trace elements. Except for inorganic carbon which exceeds requirements the remainder all exist in close to the colTect proportions for marine algal growth. By the end of March however these become so depleted in the photic zone that productivity falls to a low value and stays low for most of the growing season. The nutrients still exist below the photic zone but can only rise by slow diffusion. The invention will bring these nutrients to the photic zone rapidly to maintain productivity at a high level throughout the growing season. This will provide the food fish require and so fish stocks will be increased. At least a doubling of fish stocks in cultivated areas is promised as compared to the natural state. Furthermore the eating and dying of phytoplankton is known to sequest carbon from the atmosphere and the study that has been made has predicted that the carbon credits for which ocean cultivation would become eligible will cover the capital and operating costs that need to be met.

These statements are supported by Figures El to E4 providing data that can be used to explore and design apparatus of the kind described in this patent specification. Fig.El gives a plot using data from Helmuth Thomas, Yann Bozer, Khalid Elkalay, Hem J.W. de Baar (2004): Enhanced Open Ocean Storage of CO2 from Shelf Sea Pumping: Assessment qf the processes controlling seasonal variations qf dissolved inorganic carbon in the North Sea: Science VoL 304.pp.lOO5-1007 14/5/2004 Fig.El shows how measurements of inorganic carbon such as CO2 vary with depth.

In winter diffusion provides an almost uniform concentration but in summer it is greatly depleted near the surface but below a 30 metre depth the concentration is increased. As the author's state this is caused by the growth of phytoplankton which absorb all required nutnents including carbon and so cause dep'etion. Since in sunmier a shift away from equilibrium with CO2 concentration in the atmosphere has resulted the sea now absorbs carbon from the air. This data has proved that carbon sequestration occurs by this means and the invention will further reduce CO2 concentration at the surface to enhance the sequestration of carbon.

That enhancement can occur is shown by the lower wavy curve of Fig.E2 derived from data provided by Joint I, Pornroy A (1993) Phytoplankton biomass and production in the southern North Sea. Mar Ecol Prog Ser 99:169-182. This curve shows how the phytoplankton Hoorn from the beginning of February until the end of March as light increases but then the bloom ends with productivity plunging during April and staying low until nild September. This is despite the greatly increasing amount of light available as shown by the upper solid curve superimposed by Pearson. This starts with the light intensity at noon on the equator outside the atmosphere of 1,356 watts per square metre with reductions due to latitude and time of day and takes account of increase in day length at 54 degrees North. Then this intensity is multiplied by a factor of 0.3 to allow for absorption in air clouds and reflection from the sea. This provides the light available but this is then multiplied by 0.01 which is the efficiency of photosynthesis of marine algae according to experiments of the biologist Professor Pirt. This provides the light limited growth curve based on the same units as the experimentally derived curve. Both curves provide the rate of carbon uptake in grams pci' square centimetre per day. The farmed area quoted later is based on adding nutrients at a rate increasing this uptake by I gC/m2/Day from the end of March to the end of October.

The low productivity is due to the depletion of essential nutrients such as phosphate nitrate and trace elements. Fortunately these are all present in the correct proportions except for carbon which is in excess of requirements. It is therefore only necessary to consider one representative element and the one selected is phosphorus P. Data from Phosphate, nitrate, density cent ral North Sea: Mar. Ecol. Prog. Ser. Vol.126: pp247-256 1995. (station 12). is shown in Fig.E3 and in Fig.E4 density variation with depth given for the same location is provided. These two curves need to be used together for establishing the best depth from which to mine nutrients. The greatest P concentration is at 140 metres but the density difference can be converted to a static head that needs to be overcome and this is about 9 centimetres at that depth. At 60 metres a zero value of static head is indicated and so is chosen as the optimum depth. In case a linear variation from depth to surface applies in other parts of thc sea, as shown by the dashed line, this has been used in the performance evaluations to be presented just before the list of figures. This makes the static head to be overcome only 1 centimetre.

If the invention incorporates a prime mover that consumes fuel then some carbon dioxide is generated. However the assessment given in Patent Application Number GB1210097.0 and supported by the simple evaluation given here before the list of figures has shown this release to be less than 2 percent of that sequested although this figure is not to be considered as limiting in any way. The invention can however be further developed to provide a source of energy from harvesting algae either being phytoplankton or floating species of seaweed. The latter reproduce by vegetative means. Sargassum fluitans and natans float around the Sargasso Sea reproducing in this way. Both of these feedstocks can be processed to fuels such as natural gas and crude oil. Natural gas can be generated by anaerobic digestion and then all nutrients can be recovered for recycle. Cleady only a small fraction of the harvested crop needs to be consumed by the cultivating machinery. The fuels provided in such ways will project CO2 into the atmosphere when burned but having removed it from the sea in the first place the process is carbon neutral. This is no better than using land based biomass but another factor arises that provides a unique advantage. Only about half the algae can be harvested to make fuel. The remainder will be eaten by fish and ultimately discharged as sequested carbon in their excreta. In this way a large net sequestration can be achieved. The result is to provide a means for solving the major environmental problems of food and energy with net carbon sequestration at zero extra cost. Furthermore when applied on the large scale in the open ocean these advantages can be economically applied on the huge scale that is required. Then again the depletion of CO2 over large areas of the ocean will cause concentration gradients to arise for that gas in both air and sea so reducing the acidity of the sea that is of environmental concern. No other proposal has yet been published having this combination of advantages that are able to be realised on an adequate scale and at the same time promise to be economically viable.

Other proposals for ocean cultivation have been made and some tested in which pumps have brought up nutrient carrying seawater in long pipes. The results have proved that fish stocks can be increased by such means. However such apparatus is readily shown to be very expensive in both capital and running cost. Indeed the example provided ater shows that for the same economy of energy sacrifice a pipe 33 metres in diameter containing a pump impeller of this size would be needed to provide the same output and energy economy as an inverted hydrofoil of only 12 metres span towed by a tug boat no bigger than a canal barge and having a propeller of only 3.4 metres diameter. Unless a commercial profit can arise from operation it is not possible to implement solutions to global problems on a meaningfull scale.

Towed hydrofoils require only a small fraction of the power needed to operate pumps in pipes of acceptable diameter and also have greatly reduced capital costs. Furthermore pipes cannot travel fast enough to spread the nutrients evenly over the area being fertilised. In consequence the present invention will be commercially profitable and so offers a practical means for ocean cultivation.

To do so requires the initial small scale operation in the North Sea, whilst being an economically viaNe enterprise in itsdf, is also to be regarded as a pilot operation for expansion to large scale apparatus suitable for the cultivation of oceanic gyres. These are so depleted of nutrients in the photic zone as to render them the equivalent of land deserts. Their cultivation will not therefore present unmanageable hazards to the marine eco system. The required nutrients exist iii adequate concentration at depths below about 300 metres and this invention provides an economic means for introducing them to the photic zone. Since this depth is about five times that for the same concentration in the North Sea if follows that about a fivefold increase of scale will be required for appllcation of the invention to cultivate parts of the deep ocean. Operation in the North Sea can therefore provide the equivalent of a pilot plant study for extension to provide the storable and sustainable energy materials and fish on the vast scale needed to solve major global problems. Implementation on this scale would simultaneously prevent increase of the carbon dioxide content of the atmosphere that is considered a major source of undesired global warming.

The present improved invention has a tug boat powered by some form of prime mover such as an engine or an electric motor and optionally assisted by a wind turbine to provide the motive power for towing a hydrofoil to be called an uppingvane at negative incidence and suitable depth in the sea. This means operating the uppingvane with its leading edge at greater depth than its trailing edge. The more cambered surface of the uppingvane forms its bottom surface. The result is to propel a plume of seawater having an adequate concentration of the nutrients required for the growth of marine algae to the photic zone of the sea.

The reason for the high efficiency promised by the invention is that the plume has a cross section known as a Kelvin oval whose internal structure consists of a vortex pair. The outer surfaces of these vortices move almost at the same speed relative to the moving plume as the external fluid through which it is propagated. k consequence friction is minimal. This accounts for the very great distance of penetration such ovals are known to exhibit.

High waves are frequently encountered though they rarely exceed 4.5 metres as measured from trough to crest. The improved invention is concerned with a simpler and cheaper means for accommodating waves than were described in the previously mentioned patent application. It consists of the addition of a so called cable float that is towed behind the tug boat in a submerged state by a towing cable and the cable float supports the uppingvane by a connected main cable. When a conventional tug boat is provided the towing cable is deployed from the stern of the tug boat. The line of thrust from the propeller and that of the towing cable then produce a couple causing the stern to be depressed. A tug boat oflarger displacement than is otherwise required results as a consequence. However a conventional tug boat can be used with the improvement this invention provides for initial trials.

Specially designed tug boats are preferred for achieving best economic viability. This will minimise the couple previously explained with consequent reduction in size of tug boat needed. To achieve this the invention provides an alternative coupling point of attachment of the towing cable that makes the couple formed by towing cable drag times distance of its line of action to the coupling point equal but opposite to the couple produced by tug drag times its line of action to the same coupling point. This dictates a coupling point on the skeg or pod below the thrust line of the propeller. The skeg is fixed to the bottom of the hull of the tug boat and supports the pod in which the propeller shaft is mounted.

The energy needed for propulsion can be provided by fossil fuel although a main long term aim is a change to sustainable resources. For example a wind turbine or a large solar panel can be incorporated to charge a large battery that can then supply an electric motor. However a more economic alternative is the provision of fuel derived from phytoplankton or the floating varieties of seaweed that can be cultivated as part of the output provided by the invention.

The improvement is related to the previous Patent Appfication Number GB 1210097.0 that describes a specially designed tugboat incorporating a cable extending largely vertically downward and attached at its bottom end to the uppingvane. To enable operation in rough seas the cable is deployed from a winding drum that is able to rotate first in one direction and then the other by being operated by hydraulic apparatus.

The improvement described in the new invention avoids incorporation of a winding drum having such an expensive mechanism needed for countering wave effects. The improvement enables operation in rough seas by adding an extra cable to be called a towing cable to tow a so called cable float. The cable float consists of a buoyant object of sufficient displacement so that the net down force produced by the uppingvane is supported. Attached to a rearward facing surface of the hull of the tug is the leading end of the towing cable which is attached to the cable float at the trailing end. Then a second cable to be subsequently called a main cable is attached at its upper end to the cable float and at the bottom end this main cable attaches to the uppingvane.

In normal operation the cable float will be pulled down to a shallow depth by adjustming incidence of the uppingvane and of power to at least one large propeller of the tug boat. The towing cable will then have only a small inclination to the horizontal direction and operate at a shallow but adequate depth sufficient to be hardly influenced by waves.

The towing cable inclination to the horizontal will oscUlate however as the tug boat rises and falls but with the cable float constrained to small vertical movement by its coupling to the uppingvane. Then since little change in the vertical component of force is transmitted to the uppingvane the latter is little affected.

The in am cable however will deploy at a small angle to the vertical. This angle will subsequently be refelTed to as the main cable angle. For the case of an uppingvane having neutral buoyancy the tangent of the cable angle at the point of attachment to the cable float is the drag of the uppingvane divided by the downward force produced by it. In consequence the two cables automatically set at an obtuse angle to one another. Unfortunately waves cause horizontal oscillating motion of the tug boat as well as vertical motion and so an undesirable oscillation in the main cable angle will result. The cable float will swing in an arc centred on its point of attachment to the uppingvane. Such oscillation causes a cyclic change in the horizontal component of cable force which is the towing force acting on the uppingvane. This variation is undesirable since it causes the uppingvane to speed up and slow down which impairs its effectiveness.

The arc of oscillation and its associated change in main cable angle will be almost directly proportional to the amplitude of horizontal wave displacement. However, the variation of towing force at the uppingvane is determined by the change of this angle as a proportion of its time average value measured from the vertical direction. If this average angle can be increased then the fluctuation in towing force will be reduced.

A reduction in towing force fluctuation is achieved in a preferred though not essential embodiment of the invention. This improvement is made by reducing the down force on the cable float by providing the uppingvane with positive buoyancy so increasing the ratio of towing force to down force as compared to an uppingvane of neutral buoyancy. The result is an increase of main cable angle as measured from the vertical.

By way of example but not to be considered limiting in any way a ratio of towing force to hydrodynamic down force of 1/8 is typical. If the density of the uppingvane is reduced from the seawater value the buoyancy so provided is readily able to counter 2/3 of the hydrodynamically induced down force. Then only 1/3 of this force remains to be carried by the main cable. The aforementioned ratio becomes 3/8 so reducing the variation in towing force to about 30% of the neutral buoyancy value.

Even though the reduction of the mass of the uppingvane from one of neutra' buoyancy has reduced its inertia analysis has shown speed fluctuations due to quite large waves will be acceptably small.

Since the cable float has less to support by the amount provided by buoyancy of the uppingvane a further advantage is the reduced size and drag of cable float required.

A chcap way to make both a cable float and uppingvanc of fight wcight is provided in the invention. A two part mould is provided made from a cheap material such as concrete.

Then after lining both halves of the mould with plastic sheets and in the case of the uppingvane inserting the metal reinforcing plates where required to form the main spar and adding any concrete ballast required the two parts of the mould are closed leaving a small gap to allow air to escape. Then structural foam is forced into the space between the two plastic sheets until they press against the mould surfaces. Structural foams are available having a specific gravity as low as 0.22 yet are able to withstand pressures at depths of up to 900 metres in the sea. So application of the invention even in the open ocean is permissible. A suitable strong plastic can be chosen for lining the mould. Then the components will be provided with tough and durable skins. The two reinforcing plates can be joined by vertical plates if found necessary. Then this assembly forms a very strong and rigid box spar.

An alternative kind of cable float is provided in the invention as an inflatable one.

This can be made from rubber or plastic and is inflated at the surface so that its cross section is then almost circular. The wall thickness is made non uniform being thickest in the region of its upper and lower parts so that when pulled down to about ten metres the air inside will be compressed causing the shape to become more oval with long axis vertical.

The cable float is of streamline shape in order to minimise drag and can have a circular cross section as viewed in the direction of motion. Some vertical motion will be induced by wave motion especially now that the net down force has been reduced.

Consequently a circular cross section may no longer be the best shape. An oval cross section with long axis vertical and possibly with pointed top and bottom edges can be provided, If containing structural foam extra voids can be provided during the foam filling process by the suitable positioning of inflated bags. This reduces weight and cost. Attachment to the towing cable is provided by a so called Y member consisting of a metal tube to be called a towing tube having a bore matching the external diameter of the towing cable that is inserted and fixed preferably by the brazing process and two bifurcated arms extend backwards from their joining point and have bearing housings at their rear ends. Replaceable bearing shells are fitted inside the bearing housings preferably made of water lubricated material such as nylon.

These two bearings cooperate with a cylindrical shaft having a horizontal axis that is also alTanged perpendicular to the towing direction and located in bores provided in the structural foam of the cable float. This cylindrical shaft that can be hollow has its axis positioned at a point close to the centre of pressure of the cable float. What will be called a lug has a main tubular extension, the main tube, into which the main cable is fixed preferably by brazing.

The lug has a bore matching the cylindrical shaft and a radial extension of the lug forms a flange the latter having a radial slit and a hole is provided through it for a clamping bolt. This enables the lug to be clamped round cylindrical shaft with the lug situated between the two bearings connecting to the towing cable. The main tube is locked in place by the structural foam in the first two embodiments and so the only angular motion relative to the cable float is that of the towing cable.

Access to the beanngs is required for maintenance that requires periodic replacement of bearing shells and three alternative means are provided in the invention.

In the first embodiment the two bearings are arranged as close as possible to the central lug and so lie inside the caNe float. This is made as a major part with minor part existing as a core of prismatic shape. The latter fits closdy inside a cooperating hole in the major pfl. This core can be removed so that the lug can be unclamped for removal of the cylindrical shaft so that the bearing shells can be replaced. The towing cable is allowed relative angular movement by a slit provided in both the core and the major part.

In the second embodiment the two bearings are located externally with respect to the cable float and the two arms of the Y member together with the integral cable tube connecting with the towing cable all exist outside the cable float. No core or slit is required or provided and accessibility for maintenance is simplified. The bearing housings are split so that removable bearing caps allow for the removal of bearing shells. To minimise hydrodynamic drag the external shape of the end of the cable float in front of the cylindrical shaft is made to be a close fit with the inside shape of the Y member for motion matching all but veiy high waves. This configuration minimises drag.

To eliminate sfiding friction aliogether the bearings can be made with very large clearance so that they become eyelets and pivot. Both surfaces in contact are then made from hard materials.

It is also possible to eliminate bearings and the need for their maintenance by providing flat springs made from a material such as high carbon spring steel. The shaft need no longer be cylindrical but needs to encaster the springs. The shaft can be made in two parts of prismatic cross section that nest together to act as a clamp for the springs. Bolts or rivets are provided passing through both sections and the trapped springs. The springs are made thin in the direction perpendicular to the axis of the shaft but wide in the direction parallel to that axis so that an adequate cross section is provided for transmitting the load from the cables but limits bending stresses to low values. The springs thicken and narrow toward their points of attachment to the cables and teiminate in cable tubes into which the cables are fixed. A single spring centrally mounted on the shaft connects with the main cable whilst two spnngs attach outside the cable float to form a pair of arms that meet where the towing cable is attached.

Experiments have shown that an uppingvane needs at least one stabilising fin positioned close to its trailing edge and having its surfaces oriented largely in a vertical plane and in line with the direction of motion. In one embodiment found to be satisfactory from experiments on a model the plan form of the uppingvane has a straight trailing edge but the chord is greatest at its centreline reducing to only a small fraction of this value at each tip defined as the maximum distance from the centreline of the uppingvane to the point where a fin is attached. At each tip such a fin is attached and each fin is arranged at an obtuse angle less than 150 degrees with respect to the lower surface of the uppingvane.

Three alternative embodiments of the invention are provided to counter stability and other problems.

With a point of attachment of the main cable confined to the mid span of the uppingvane the tendency exists for motion in banked turns.

In the first embodiment to prevent this the invention provides two links each attached at equal distances from the nose or most forward point of the uppingvane and at equal distances from its centreline. The two links are joined at their uppermost ends where an attachment to the main cable is provided. Each link is connected by a swivel joint to a main spar embedded in the uppingvane and attached preferably by welding to a metal sheet that forms part of a main spar. Then the pair of links is aNe remain in the line of the main cable as viewed in side elevation. Experiments have shown this arrangement provides satisfactory lateral stability.

A longitudinal instability is also generally encountered. To explain the longitudinal stability problem it will first be assumed that the line joining the lower ends of these links is positioned where the centre of pressure exists at stalling incidence. Then the centre of pressure moves backward i.e. toward the trailing edge as incidence reduces from stalling value to operational value. The uppingvane then goes out of control without preventive measures being applied. It is to be remembered that the lift force is vertically downwards so a negative incidence is needed to produce a down force. Hence something is required to prevent the trailing edge moving down.

In this first embodiment the two links are attached to the uppingvane near where the centrc of prcssure occurs at stall. Then to counter the down force near the trailing edge at less than stalling incidence a tension cable to be called a weak cable is attached at its lower end to a point on the centreline of the uppingvane and toward or close to its trailing edge. The upper end of the weak cable is attached to the main cable at some optimum position that is generally at a higher level than the point at which the pair of links join and couple to the main cable. A sleeve is provided attached to the weak cable by a clamp with this sleeve being made with a sliding fit around the main cable. The sleeve has a longitudinal split flanked by a pair of flanges having a clamping bolt so that the sleeve can be clamped around the main cable in any desired position along its length.

The position of the centre of gravity is not important when a weak cable is incorporated. Indeed this centre can be well behind the centre of pressure.

In the second embodiment no weak cable is provided. Instead an extra pair of stabilising hydrofoils is provided located on or close to the nose of the uppingvane. They protrude one on each side being aiTanged in a horizontal plane and are preferably fixed to a common cylindrical mounting shaft so that incidence can be adjusted to produce a balancing down force near the nose. To provide bteral stability the two finks attached to the main cable are retained as described in the first alternative.

In the third embodiment a single link is provided connecting the main cable to the uppingvane at mid span. A hole at its bottom end cooperates with a pin and mounting flanges the latter being fixed to the main spar provided close to the upper surface of the uppingvane.

The position is chosen corresponding to that of the centre of pressure at design incidence. It is possible to provide stability by a fixed geometry such as by having reflex trailing edges and by providing dihedral but some sacrifice by extra drag has then to be accepted. An alternative that avoids such sacrifice is provided in the invention. An elevator is provided attaching to the trailing edge of the uppingvane and extending almost to both of its tips. The elevator is arranged to bend up or down by a warping means and can also twist in order to provide ailerons as well. Then both longitudinal and lateral stability can be maintained and in the embodiment to be described automatic means are provided. However, control of incidence can optionally be provided from the tug boat by an actuator in the uppingvane operated through an insulated electrical cable that uses the main and towing cables for the return circuit, The elevator has a thin horizontally orientated metal sheet extending from its rigid attachment to the uppingvane and dividing this elevator into an upper and a lower hollow chamber. Both upper and lower external walls are made of more flexible material such as rubber so that when a pressure difference is applied across the metal sheet it is caused to bend. The end wall of the elevator remote from the trailing edge is formed as a recess or can be a pipe with a muhipl icity of connecting holes and adds more vertical cross sectional area to the two chambers. This permits fluid to travel inside the two chambers in a spanwise direction. The outer flexible walls can have vertical walls with holes in them attaching them to the central thin metal sheet if found necessary. Alternatively the elevator can have outer walls made of a rigid material connected to bellows whose opposite ends are fixed to the uppingvane and with the interior of the bellows forming the upper and lower chambers.

Two tubes are provided one connecting with the upper chamber and the other with the lower chamber. These are the upper chamber tube and lower chamber tube respectively. The upper chamber tube extends to a point as close as possible to the nose of the uppingvane where it ends at a bellows section closed by a vertical end wall or a thin diaphragm can be provided made of flexible material such as rubber. Exterior to the bellows component is a containing chamber filled with seawater and is connected through a port to the seawater outside so that the pressure outside the bellows or diaphragm is maintained close to that near the leading end of the uppingvane. The upper chamber tube and bellows unit forms a hermetically closed internal volume and contains a dense liquid such as tetrabromoethane.

This liquid has a density of 2.97 g/cm3 as compared to 1.028 g/cm3 for seawater and so this internal liquid has a pressure change with depth 2.88 times as great as seawater. The lower chamber of the elevator and lower chamber tube is filled with seawater and is connected to the containing chamber. At this point the pressures in both tubes are equal to the pressure of the sea outside. Then as one tip of the uppingvane rises and the other falls the higher elevator bends up and the lower one bends down. A restoring torque is produced so that movement toward the horizontal direction is produced.

When the negative incidence is increased the pressure inside the upper chamber of the entire elevator reduces more than in the lower one. This causes the elevator on both sides of the centreline to bend up so tending to restore incidence to the desired value. In this way stability in both yaw and incidence is achieved. The rubber upper and lower outer walls of the elevator provide a muscular kind of action with no rubbing parts involved.

Two or more upper and lower chamber tubes can be provided to connect with the upper and lower chambers of the elevator at well separated points to increase the speed of response. All upper chamber tubes can connect to a single bellows with all lower chamber tubes connect to a single containing chamber surrounding the bellows. Two sets of bellows can be provided close to each other with each connected to a separate elevator disposed one on each side of the centreline of the uppingvane and each provided with a servomechanism as described next so that banked tunis can be effected.

In order to control incidence a servomechanism is provided that connects to the electric circuit so that it can be controlled from the tug boat. The servomechanism has an operating rod that connects to the end wall of the bellows or diaphragm. This adds or deducts some pressure inside the upper chamber so that the elevator is uniformly deflected.

If incidence control from the tug boat is not required the operating rod can be provided with a threaded end where it attaches close to the nose of the uppingvane and extends outside. This enables fine adjustment of incidence to be made.

The tendency is for the centre of gravity of the uppingvane to be a long way behind the centre of pressure and this is unsatisfactory for embodiments 2 and 3. The ballast needed to prevent excessive buoyancy therefore needs to be concentrated near the leading end. A nose piece can be provided if necessary that is filled with a heavy substance such as concrete to trim the balance.

For all three embodiments described a means for towing to the site of operation has to be provided. If the two cables remain attached the uppingvane and cable float need to be towed on the surface in shallow water. It is also preferable to operate the uppingvane close to zero incidence for reducing drag. A nose ring fixed to the most forward point of the uppingvane is provided and the link or links are made of such length that when turned to almost the horizontal direction they extend just beyond the nose nng. This provides the towing on surface position. A clamp is provided that has a spigot that can be passed through the nose ring and a flange is provided at its upper end to hold down the link in its required position. A cover plate is also provided for positioning on the side opposite the clamp and is locked in place using cotter pins. The links can be formed in the shape of arcs as seen in side elevation in order to reduce the distance from main cable to nose ring when in surface towing mode.

Waves need to be stopped from causing snatching during surface towing mode. The towing cable can be wound in on a drum if required but not the main cable if the cable float remains attached. The effect of towing speed has to be considered. The main cable will hang in a curvc such as a catcnary whcn bcing towed. By way of example only and not to be regarded as limiting a study has shown that if the cable is 60 metres long and for normal operation has a stress of 20,000 lb/in2 (.6895.5 N/ni2 = 1 lb/in2) then it will sag only by 6 centimetres at its centre. To accommodate waves this stress has to be drastically reduced. If the stress is reduced to 1/20 of the previous value then the sag will increase to 4.9 iii and the horizontal distance will shorten by 1.2 m. This then is the Umiting horizontal wave induced motion for that condition requiring the towing speed to be reduced to about hail the design value. The higher the waves the slower the safe towing speed will be.

Close to port and in port speed has to be reduced so that the cable will hang so low as to foul the sea bed if not prevented. Therefore close to port a number of inflatable air bags are provided to be clipped onto the cable. These provide the support required.

If the towing cable is not wound in it will also need air bags for temporary support.

Also being of much lower weight it will have a higher stress than the main cable during surface towing and will therefore not hang so low as the main cable. In consequence without some additional component the towing cable will provide the limiting towing speed. To increase the permissible towing speed to the limit set by the main cable the invention provides an optional addition that can either be eft permanently in place or removed after changing to operational mode.

This additional component consists of a hanging weight clamped in a central position on the towing cable and consisting of three parts. An upper part is arranged to fit above the towing cable and is as light in weight as possible but has an arc shape to prevent the towing cable bending with too small a radius. This arc is centred at a point above the cable. Also the arc has a grooved profile to ensure this cable remains trapped in the groove. On each side of the said upper part a flange extends to a point below the cable and holes are provided so that at least one clamp bolt with axis perpendicular to the cable can be inserted for trapping the cable. A lower part that is much heavier than the upper part is also provided to hang from the clamp boils. In order to minimise the weight required a pair of hydrofoils are also optionally provided to produce an extra down force. These hydrofoils are mounted on a cylindrical shaft having a horizontal axis that is also perpendicular to the towing cable and is fixed to either the upper or lower parts. The hydrofoils have bearings cooperating with this shaft the bearings being fixed within the hydrofoils and located with their axes between the leading edges and centre of pressure at stalling incidence. Incidence locking bolts are provided to fix the hydrofoils at a negative incidence for towing to the site of operation. At this site the additional component can be removed or left in position. When designed for being left in position the hydrofoils have symmetrical cross sections and the incidence locking bolts are removed on site. Then vertical oscillations caused by waves produce angular oscillations of the hydrofoils in such manner as to produce extra thrust. The way this works is described in a later section where a similar principle is involved. In this way wave power is utilised. For optimum operation in this mode the upper part can be exchanged for one offering much lower drag.

All these extra problems have arisen as result of having a cable float and so a further and now preferred embodiment of the invention is provided. A streamlined cable float spar extends from the lower surface of the cable float. This spar is fixed with its axis substantially vertical and at least almost intersects the centre of buoyancy of the cable float under normal operating conditions of upwelling. Close to its lower end this spar bifurcates into two arms to form an inverted Y piece with bores near the ends of the Y to cooperate with a horizontal shaft also aligned perpendicular to the towing direction. At the centre of this shaft a lug is positioned or even clamped in position by the provision of a clamp bolt the lug having a split in the plane of the shaft axis. Integral with the lug is an extension to a main tube inside which the main cable is fixed. Either side of the ug are a pair of bearings mounted in the arms of a towing Y piece that is made integral with a towing tube inside which the towing cable is fixed. A single winding drum is provided inside the tug boat around which both cables can be wound.

By this means in normal operating mode the towing cable can pivot to make angular oscillations so providing the means for coping with large waves.

The central lug and the bearings for the towing cable can be provided with a much larger internal diameter than the horizontal shaft with both cooperating parts made from a hard material. Then instead of sliding a rocking motion is produced to eliminate sliding and so reduce wear and associated maintenance requirement.

Alternatively to eliminate sliding contact flat springs can be provided extending from the horizontal shaft to the towing and main cable tubes as an alternative to having bearings that require periodic replacement.

It seems necessary to provide a description of the way a fleet of units of the kind described would need to be operated since details of the invention have been dictated by the overall plan. The following description of this plan is to be regarded as non limiting being provided only by way of example.

When outward bound from port both cables being temporarily connected by a pin which can be the same horizontal shaft are stored wound on the winding drum. The uppingvane is directly attached to the stern of the hull of the tug boat by eyelets or by a rigid bar connected by eyelets at each end so that angular motions are not restricted and the cable float is either carried on the tug boat or clamped on top of the uppingvane. In this mode waves of any height can be accepted. On reaching the site of operations the main cable is connected to the link or links of the uppingvane and the main cable is allowed to pay out until the towing cable emerges and reaches the surface of the sea. Then the horizontal shaft which has been temporarily fitted to connect the two caNes is withdrawn and re-inserted with the Y piece of the cable float now iii position. So the cable float is now deployed. The towing cable is then fully extended and connected to its towing lug on the tug boat. The unit is now arranged for deployment in normal operating mode to provide upwelling. The reverse procedure is adopted for the voyage back to port. Slings for supporting the heavy cables from the tug boat are provided for holding them temporarily in position during these procedures.

For full economic viability a fleet of twenty units is required so that all can be managed with a single maintenance crew when each unit is operated by remote control or as a robot with no crew on board. Then a boat is provided that is calTied to site on the tug boat to be used so the crew needed for deployment can return to port in order to deploy the next unit.

This process continues until all units are on site at the start of the growing season. At least one of the crew needs to be able to operate as a diver though only to a depth less than about six metres. Then the same crew carries out maintenance of the fleet on a one each day basis until the end of the season. The crew then operate from a small tanker that contains enough fuel for the whole fleet when each is refuelled once every three weeks and refuelling is part of the maintenance procedure. One day of the three week schedule is allowed for return of the tanker to port for refuelling. During the winter months with the fleet moored in port the same maintenance crew carry out such tasks as removal of bio fouling deposits.

In this way a sma'l crew is able to operate a marine farm in the North sea covering an area of about 500 square kilometres when operating uppingvanes each of 12 metres span.

A problem arises when the engine is shut down for its 500 hour maintenance and re-fuelling during the growing season. This means once every three weeks. Under such conditions the weight of both towing and main cables tends to draw the tug boat cable float and uppingvanie together so that wave induced collision can result. The invention provides a means for preventing this by use of wave energy to provide some propulsion. Hydrofoils of symmetrical cross section are mounted one on either side of the hull of the tug boat near the bow. The position can be on an extension to the bow in order to amplify vertical wave induced motion.

A horizontal cylindrical shaft is arranged perpendicular to the longitudinal axis of the hull and extends equal distances from the centreline. The hydrofoils have internal cylindrical bearings cooperating with the shaft and located on their axes of symmetly and at a position between their leading edges and their centres of pressure at stalling incidence. Then hydrofoils tend to line up in the direction of relative water velocity. This is resisted under wave conditions by the moment of inertia of the hydrofoils so that at all times they operate with an incidence that provides mostly a forwardly directed component of force. Then some tug boat speed will be provided that will prevent collision with the cable float. Some supplementary wave power will also be provided during normal operation and so can be expected to provide a small economy of fuel. In order to cater for waves mostly coming from a beam wise direction it is preferable to allow the two hydrofoils to move independently of each other but this arises naturally as a consequence of the way they are mounted independently on a common shaft which can preferably be hollow.

It may be desirable to increase the phase lag of each hydrofoil. They can each therefore be optionally provided with a dashpot to provide a controllable amount of damping and are known art. For example the bearings can extend inside the hull forming hollow cylinders. A rod or vane can extend in a radial direction from the surface of each cylinder.

These vanes cooperate with a close fitting casings fixed to the inside of the hull and having a fine clearance around the hollow cylinders. The casings have end walls ananged at such positions as to permit adequate angular motion of the hydrofoils. The closed chambers so formed are filled with oil. The vanes divide each casing into two chambers but these are interconnected by a pipe containing an adjustable throttle valve. By opening this valve more the degree of damping is reduced.

Torsion springs can also be provided as an optional extra if found necessaly.

The cheap method of manufacture that provides a tough plastic skin and structural foam filling for both cable float and uppingvane can also be adopted for the tug boat. In this case the hull is a shell of structural foam sandwiched between two skins one outside and one inside. When the long term objective is attempted of providing energy and materials from seaweed and taking into account the increasing need to conserve finite resources of metals it will become necessary to extend the use of plastics made from the sustainable seaweed resource.

It is desirable though not essential to have the tug boat purpose built to minimise size weight and cost. The invention also provides a mast with radio antennae mounted at the top for remote control. Cheapest operation is provided in this way since labour costs are reduced to those of periodic maintenance. The tug becomes a robot.

When the prime mover of the tug is a diesel engine the major part of the operating cost tends to be due to the fuel used. Fuel consumption can be minimised by providing supplementary energy as electricity from a large solar panel or from electricity supplied by a wind turbine. An electric transmission is provided with at least one low speed electric motor direct coupled to a propeller. If a diesel engine is still provided then this also has an alternator provided which is direct coupled to the engine output shaft. A large battery can be provided of such capacity as to store sufficient sustainable energy from wind or light as to provide totally fuel free operation. However, such total reliance on sustainable energy is not likely to be economically viable. A cheaper alternative could be provided by producing fuel from part of the biomass generated by the marine farming operation.

One cmbodimcnt of thc invention has a vertical axis wind turbine of novel kind whose vertical shaft has the rotor of an alternator fixed to its bottom end. The electrical output is connected to a motor mounted on the same shaft as a propeller so that the equivalent of a reduction gear is provided. Any excess power provided as alternating cunent by the wind turbine is connected through rectifiers to a storage battery. A fuel consuming engine is also provided also having an alternator directly connected to its output shaft and the electrical output is also connected to the same motor. The two alternators combine to form part of an electrical power transmission system so that both or either can provide current to the electnc motor whose rotor is fixed to the same shaft as a large propeller. In this way as a preferred embodiment of the invention no mechanical gearing is incorporated.

The vertical axis turbine has the advantage of being provided with blades that can be feathered in such a way that under high wind conditions the drag force is reduced as wind speed increases even though the power it generates remains constant. The turbine blades are provided with pitch control. Further advantages are that more than two blades can be provided to yield a very much reduced cyclic torque variation than is possible when only two blades are incorporated. Operation at the very high wind speeds classified as violent storms on the Beaufort scale is permitted. Under these conditions it should be possib'e to maintain operation with power being produced up to wind speeds of 35 metres per second. No shut down facility is required and so is not provided. Most turbines are shut down when wind speed exceeds 25 mIs.

The blades are pivoted for maintaining constant power regarWess of wind speed. In extreme wind conditions the control means provided can actually reduce rotational speed so that centrifugally induced stresses are reduced to allow a greater margin for the transient stresses caused by gusts. Blade pivots are provided for pitch control and this also promises to increase turbine efficiency whilst permitting lower peripheral blade speeds to be used.

This greater than two turbine blade embodiment of the invention provides a turbine with pivoted blades with apparatus to adjust their pitch. To reduce the turbine radius to a convenient value it is desirable though not essential to have a design blade speed not greater than about 2.5 times the design wind speed usually chosen as 11 metres per second. To achieve pitch control each blade is carried in bearings having a vertical axis so that the blades of symmetrical aerofoil section are able to pivot.

Full details of this kind of vertical axis wind turbine are provided in our Patent Application Number: GB1208480.2 dated 15/05/2012 Ref: RDPO712IO.

Showing why uppingvanes: inverted hydrofoils, offer such good economy Ihe figures given in the following are to he regarded as by way of example only and not limiting in any way First a simple calculation -by energy accounting At 60 m depth in the North Sea data gives the phosphorus content in PU4 as PQ =40 mg/m3 Now the Redfield formula for marine phytoplankton is: [(CH2O)rn5(NH3)16(H3P04].

From this the P content Ph/s in such algae becomes 0.87% by weight of fully dried biomass.

So the dry biomass output per cubic metre of sea becomes: 0.0410.0087 = 4.598 Wm3 Pearson's bomb calorimeter measurement of dried algae heating value FICV = 17,400 JIg But this contained condensed water whose btent heat needs deduction to give the useable lower calorific value LCV = 15,800 J/g EM,, the useful energy available per cubic metre of seawater = 4.598x 15,800 = 72,648 JIm2 Hence for upwelling flow of Q = 1 m3/s the rate of energy output becomes: Ehio=72,648 W From a detailed analysis for overcoming a static head of 0.Oim due to density difference between 60 rn and the surface and allowing for a mixing loss to leave a speed of 0.2 mIs at the surface the plume needs to be projected with a vertical speed of: = 0.5478 mIs (Note that this is pessimistic since availaNe data (Fig.E4) shows no static head needs to be overcome for 60 iii depth. Mixing assumes 1 cm growth of each edge of the plume per iii of vertical travel. This low growth is due to the vortex-pair inside the plume. A simple example is the contrail left by a high flying aircraft which hardly spreads at all) The pumping' head/i needed is: /i = vo2/(2g) = 0.54782/(2x9.807) = 0.0 153 m This is equivalent to a pressure difference AP=p<gxh = 1028x9.807x0.0153 = 154.2 N/m2 The ideal power W1 = APxQ. If Q = I m3/s then: WI = 154.2 Nm/s or: WI =154.2 Watts And for the same seawater flow of Q = I mi/s the energy output rate was: Ebio= 72,648Watts So the ideal energy gain ratio becomes 72,648 /154.2 = Ehio/W1 = 471 Refinement taking losses into account It is readily shown from the hydrodynamics of hydrofoils that: = DII = 1-l-6,o/u) + CDF/CL ifl0V0 (v0/ti)-/ U Where towing power W = DXu in which D = drag in Newtons N and u = towing speed rn/s And in0 is the mass flow rate in0 = px 0.75 x b2xu where b = span of hydrofoil in m.

For a hydrofoil that stalls at lift coefficient CL= 1.6 a working value of 0.8 is suitable.

Then profile drag coefficient for infinite aspect ratio CDF = 0.013. and it = 2.5 m/s is used With v0 = 0.5478 mIs. this yidds for p= 1028 kg/m3 and b = 12 m: Wfi, = 0.58031 Then an easily denved equation giving energy gain ratio EbIo1W is: p010 LCV (p0 /P)) -, = -UN = 15,800 J/g for fully dned akae w This yidds: EbioIW = 405.8 So dividing by the previous ideal value the efficiency of the hydrofoil becomes 86.2 % Overall energy gain ratio taking all losses into account A detailed study shows hull and cable drag at a = 2.5 rn/s gives an increase ratio of 1.153 An open propeller of 3.4 rn diameter for a span of b = 12 m gives an efficiency of: 70% Transmission efficiency from the engine is assumed as: 96% Diesel engine thermal efficiency at 60% full load burning oil or Cl-I4 35% Digester efficiency of algae to CH4 + CO2 from chemical balance: 76% Transport of algae and CO2 absorption plus cryogenic cooling to liquid: yield ratio: 90% (The last 90% ratio is an informed guess) Overall energy gain ratio becomes: 405.8 /1.lS3xO.7 xO.96 xO.35 xO.76 xO.9 = 56.6 Hence only 1.77% of the biomass generated needs to be used for operating the farm.

For b = 12 iii span of hydrofoil Q = 0.75 x b2xu = 0.75xi44x2.5: Q = 270 m3/s.

Comparing with an equivalent pipe and pump system For the same energy gain ratio of 406 and overcoming the same 0.01 m static head only a head of 0.0053 iii remains for overcoming pipe friction and providing flow speed. We ignore pipe friction. Then v = 0.3i3 mis, the mean speed in the pipe.

Now to compare with hydrofoil Then pipe bore = 33 m and a pump impeller of this diameter would also be required as compared to the 3.4 m diameter propeller used for towing the hydrofoil. Furthermore a static installation is demanded with nutrients relying on ocean currents for distribution.

Provisional Cost Estimate for a Marine Farm for Fish and Carbon Sequestration Fuel cost for the diesel engine is the major item and crude costs $1 l0/bbl This converts to $llOxO.6187 = £68/bbl = £681130 kglbbl = £0.523/kg.

Domestic heating oil Oct.2012 from www.boileriuice.com as delivered £0.73/kg The engine operates at 82 kW shaft power at an a thermal efficiency of 35% So energy input is 82/.35 = 234.3 kW and the LCV = 43,000 kJlkg. Hence 470.8 kg/day of fuel is consumed. So in a 7 month season and 90% time utilisation 90,210 kg is used.

Batch Production (Provisional rough cost estimate) A commercially viaNe marine farm based on the invention would consist of 20 tug boat, cable float and uppingvane units. This allows each to be serviced once every 3 weeks for the 500 hour engine maintenance needed and for refuelling by a single 6 man maintenance crew operating a small carrier starting out with 250 tonnes of fuel oil on each 3 week voyage. One day remains for the carrier to return to port for refuelling and return to site. Only 4 men are on duty at any time with 2 off duty on shore leave.

A carrier of 70 tonnes empty displacement of specific cost £7,000/tonne = £490,000 Annual cost on 20 year loan = 490,000/6.3 = £77,778 so annual cost per unit = £2,890 The total farmed area of the fleet would be 28x20x0.9(utilisation) = 500 square kilometres.

Capital cost per unit is to be based on specific costs as a reasonable first estimate.

The cost of raw sted is about £1,000 /tonne and a diesel engine of 190 horse power has a specific cost of not more than £20,000/tonne. Hence a batch produced marine unit should lie between these limits but to be conservative will be assumed as £20,000/tonne.

The capital cost per special tug of only 15 tonnes is then estimated to be: £300,000 with foam plastic cable float and uppingvane 41 m3 foam @ £35 8/m3:-i-5 te steel gives a material cost of £17,800 multiply by 3 to cover moulding cost etc. gives about: £54,000 Total provisional capital cost of batch produced tug, cable float and uppingvane: £354,000 Interest on this capital for a 20 year loan would be: £56,200 Carrier interest spread over 20 units: £2,890 Wages @ £30,000 doubled for overheads for 6 man maintenance crew cost/unit = £18,000 Total interest and maintenance cost: £77,100 hid for 82 kW engine output in 7 months fuel cost is 90,2100kg @ £0.73/kg = £81,190 Total annual cost (provisional estimate) per unit =: £158,300 No other crewing costs are involved since the 20 tug boats of the fleet operate unmanned.

A very rough estimate of Fish Yield with no biomass used for providing energy The total dried phytoplankton yield becomes = 270 m1/s x4.598 gIm1 = 1241 g/s The wet living biomass is ten times this or 12,410 gls. All will be assumed to be eaten.

If fish growth to useful size is assumed in 3 years for 1.000 fold fish mass increase per fish then a weight gain per day of 0.006 of initial weight at start of that day is required. Bascd on data from yearling largernouth bass a food input of 0,038 of that initial weight is then required (zero growth needs 0.027 gIg). Ihe weighi gain as a ratio of Food consumed = .006/.038 = .1578.

Assume this ratio applies for each Isophic level with small Fish at Ihe third ftophic level, then as ralio of phytoplankton production small fish yield = .1578x.1578x.l578 = 0.0039 of living phytoplankton production yielding 48 g/s. If half of these arc harvested then 24 gls will be eaten by the 4th opIuc level to yield 24x.l578 = 3.8 g/s. So the catch will be 24 g/s of small fish and about 3 g/s of large fish.

this converts For a 7 month growing season a 90% time utilisation lo: 440,000 kg of total wet fish per season per tug uppingvane unit. (This is extra to the natural harvest taken from 28x0.9 km2 of sea (90% utilisation) = 25km2.

If a change in law allowed a SOp/kg levy the return per season return/unit = £220,000 Excreta from the fish produce the required net carbon sequestration.

Carbon credits I Euro = £08374 and credits are provided at 9 Euros/tonne of CO2 =fl.537/te.

Carbon sequestration anses from phytoplankton eaten by fish. Costs per unit are considered.

Phytoplankton produced = 1.241 kg/s. So yield in 7 months and 90% utilisation = 20,546 te There are 0.358 kg carbon/kg dry biomass so carbon sequestered = 7.355 te But CO2 is 44/12 times weight of carbon so CO2 sequestered = 26.370 te Annual carbon credits due = £7.537x26,370 = £203,260 So even without a fish levy the estimated profit per unit = £203,260-158,300 = £44,300 Marine Farms for Energy, Fish and Carbon Sequestration It can be arranged according to a computer study that assumes a floating seaweed mass gain per day only 5% of the value for phytoplankton that by fish harvesting hail the crop can be floating seaweed -easily harvested. Tf only the latter is harvested for conversion to fuel then the previous energy sacrifice of 1.77% is doubled to 3.54%. This has to be used by the engine of the tug boat for nutrient supply to the marine farm.

The engine output required is 82kW and so the energy from seaweed as gas becomes: 56.6x0.Sx(1-0.0354)x82 = 2238 kW. At 90% utilisation this gives 10,290,000 kWh/season Converted to electricity at 40% efficiency with 8% line loss gives overall efficiency = 37% the yield becomes (a kWeh is a kilowatt-hour of electricity): 3,788,000 kWeh in 7 months.

Can the cost of fud supply be assumed equal to that of crude oil? To supp'y I kWh we need 3,600 kJ/0.37/43,000 kJ/kg = 0.2263 kg crude oil At crude oil cost=0.523/kg the price is £0.523x0.2263x 100 = 11.8 P/kWeh. This is too high since the selling price of electricity is only about 15 plkWch.

If gas as fuel input is valued at only 3.Sp/unit of electricity the return to the marine farm would be 0.035 x 3,788,000 = £132,600/year.

For a 25 day digestion time the digester volume per upwelling unit = 13,400 m3 This could mean a vessel 15 m dia. x 80 m long but, anchored to the seabed, a wall thickness of 5mm would be more than adequate. Then only 19 m3 of plastic costing £19,000 -4-fabrication would be required so the total cost would be about £60,000 needing annual interest offJO,000. This is not an impossibly large extra investment.

Fish yields and carbon credits are halved to £110,000 and £100,000 respectively but costs of weed harvesting need to be added. A single harvesting ship for the fleet could, for example, collect floating seaweed for 16 hours a day leaving 8 hours for discharge of the wet seaweed to the digester. Then 9,650 te occupying 9,650 m3 would be transported each day.

However, the total return promised is now 132,60+i iO,000+iOO,000 = £342,600 per year per unit as compared to operating costs without fuel oil of £77,100 -i-£10,000 so there is a large profit margin which should easily accept this harvester.

No recycling of nutrients from the digester has been assumed.

Recycling of nutrients released from the digestion process could increase productivity and therefore sales to power stations also increasing fish yidds and carbon credits.

Specific embodiments of the invention will now be described by example only with reference to the accompanying drawings in which: Fig. I shows a longitudinal sectiona' elevation of a tug boat towing a caNe float which in turn is connected to an uppingvane by a main cable.

Fig.2 shows a frontal elevation of the tug boat cable float and uppingvane Ulustrated in Fig. I. Fig.3 shows a cross section of the cable float as shown in Fig.1 and Fig.2.

Fig.4 shows longitudinal section of the cable float shown in Eig.3 with detail of both cable attachments.

Fig.5 shows a cross section in plan view of the cable float shown in Fig.3 and Fig.4.

Fig.6 shows a longitudinal elevation of an alternative form of cable float having easier access to bearings for ease of maintenance.

Fig.7 shows a cross section of the alternative cable float shown in Fig.6 Fig.8 shows a section in plan view of the alternative cable float shown in Fig.6 and Fig.7.

Fig.9 shows a part longitudinal section of the tug boat shown in Fig. 1 together with optiona' extra wind turbine.

Fig. 10 shows a longitudinal section of an uppingvane as shown in Fig. 1, Fig.]] shows aplan view of the uppingvane shown in Fig.l0 Fig. 12 shows a frontal view of the uppingvane shown in Fig. 10 and Fig. 11.

Fig. 13 shows a longitudinal elevation of a cable float with spar for cable connection Fig. 14 shows an uppingvane in plan with interna' stabilising tubes Fig.l5 shows a section through an elevator of the uppingvane relating to Fig.14.

Fig,E 1 to Fig.E4 give data for the North Sea used for design but are not part of the invention Rcferring to Fig. I showing a longitudina' elevation of the invention a tug boat I is shown optionally able to operate as a robot. For this purpose navigation lights and radio antenna are provided at the top of mast 2. The latter can receive position keeping radio signals so that navigation can be provided by remote control to avoid the need for a crew if this is desired.

The skeg 3 is fixed to the underside of the tug boat on which a pod 4 is attached containing means for driving a large propeller 5. The leading end 6 of towing caNe 7 attaches to a point on the skeg below the line of thrust 8 of the propellerS. This is an optimum position that allows the tug boat to be of small size and cost by making the tug drag times distance to the line of thrust equal and opposite the conesponding moment from towing cable drag. This is an optional and not an essential feature that maintains the propeller thrust line horizontal during normal operation. The trailing end 9 of the towing cable attaches to cable float 10 of streamline shape shown submerged at an optimum depth that is produced by adjusting the engine power. The trailing end 9 of the towing cable is attached by a bearing II to the uppermost end 12 of a main cable 13. This bearing 11 is mounted inside the cable float close to its centre of gravity. Main cable 13 extends downwards to links 14 that couple with uppingvane 15 and carry most of the net down force produced by towing the uppingvane at negative incidence minus the buoyancy of the uppingvane. Longitudinal stability is provided by a weak cable 16 attached near the trailing edge of the uppingvane at point 17 at its lower end and at its upper end attaches to a sleeve 18 surrounding the main cable the sleeve having a clamp bolt to fix its position. Vertical motion of the tug boat hardly affects the cable float but horizontal wave induced motion causes the cable float to move in an arc centred on the uppingvane. The dashed line 19 is the vertical direction in order to show the arc of movement relative to the uppingvane in relation to chain dashed lines 20 and 21 that show the limiting positions for wave amplitude of 10 metres. Such a wave could cause the tug boat ito rotate in a circle of that amplitude and represents motion due to a wave height of 20 metres from trough to crest. The maximum wave height ever recorded in the North Sea was 9 metres and so the invention provides adequately for the worst eventuality. Of course the partide motions of such extreme waves do not move in circles but the analysis serves to show that the invention will adequately cope with extreme conditions. At wave heights of two metres the arc of movement is reduced tenfold as compared with the example shown and most of the time wave heights are less than this. Only small changes in incidence are then induced on the uppingvane and although the towing force has a cyclic variation induced upon it the corresponding speed changes are sufficiently small as to impair operational efficiency by an acceptably small amount.

RefelTing now to Fig.2 showing a frontal elevation the tug boat 1 is shown with the frontal area swept out by one blade of the propeller 4 in one revolution exceeding the underwater frontal area of the tug boat 1. The caNe float 10 attaches to main cable 13 whose bottom end connects with the two links 14 and these attach to uppingvane 15 at widely separated points at equal distances measured from the centreline of the uppingvane. This arrangement provides lateral stability. Longitudinal directional stability is provided by downward angled fins 22.

RefelTing now to Fig.3 showing to a larger scale than shown in Fig.2 is a cross section of the cable float 10 taken at the junction or the two cables. The cross section is shown to be deeper than it is wide and has sharp top and bottom edges 23 to minimise drag caused by vertical motion though these are not essential features. The cable float has a tough plastic shell 24 filled with structural foam 25 shown by the texture indicated. Such a structure provides adequate strength for withstanding pressure due to depth of operation at low cost. A hollow centre that is open to the sea is provided for the coupling means between the two cables. A cylindrical metal shaft 26 has a horizontal axis that is also perpendicular to the towing cable 7 by fitting in bores provided in the cable float that are perpendicular to its long axis. Shaft 26 which can be hollow has a centrally mounted lug 27 clamped over it and the main cable attaches to this lug. Either side of this lug are two bearings 28 to which the towing cable is fixed. The bearings allow the towing cable vertical freedom of angular movement. Since this structure is immersed in seawater it is preferred to use a bearing fining that is water lubricated. Nylon has such a property and so offers a suitable material choice.

A modification of the arrangement shown provides simplification and allows greater accessibility to the bearings for maintenance. Instead of the cylindrical shaft 26 having is axis close to the centre of buoyancy it is placed vertically below that point being mounted on a short strut fixed to the bottom of the cable float.

Referring now to Fig.4 showing a longitudinal section of a cable float the streamline shape is illustrated and the scale provided above. This is the size needed to match an uppingvane of 12 metres span that has a positive buoyancy of 2/3 of the down force produced by towing at a speed of 2.5 metres per second. This down-force is calculated to be 152,000 Newtons or 15.5 tonnes so the cable float together with 300 kilograms of cable has to provide 5.5 tonnes of buoyancy. Then with foam and seawater density taken into account a volume of 7 cubic metres has to be provided. The lift and drag forces are carried by shaft 26 with the drag force of 19,330 Newtons transmitted through bearing 11 that sulTounds this shaft. This bearing is fixed to towing cable 7 by a surrounding cable tube 29 so the bearing 11 pivots about the shaft 26. The upper end of the main cable 13 is fixed inside lug tube 12 that is locked into the cable float structure. This lug tube is integral with lug 27 shown only in Fig.3 and 5 that has vertical extensions 28 by slitting one side of lug 27. A clamping bolt not shown is provided to enable the lug to be tightened in order to clamp round the shaft and cause the main cable 13 to be locked to the shaft 26 as well as to the structure of the cable float. Then as the angle between the two cables changes due to wave action it is the towing cable that moves relative to the cable float. To allow for this motion the forward end of the cable float is provided with a slit 30 that is wide in the vertical direction to allow room for towing cable angular motion but narrow in width. The structural foam need not totally fill the cable float since if it did so a depth of up to 900 metres could be withstood whilst depths less than only 30 metres will be experienced. To save cost at least one void such as that shown at 33 is provided by inserting a balloon in a mould used to produce the cable float before structural foam is introduced.

A modification of the arrangement shown provides simplification and allows greater accessibility to the bearings for maintenance. Instead of the cylindrical shaft 26 having is axis close to the centre of buoyancy it is placed vertically below that point being mounted on a short strut fixed to the bottom of the cable float.

RefelTing now to Fig.5 in which a sectional plan view is shown more detail is provided of bearings and lug. What was described as cable tube 29 is shown in more detail forming a Y member by being made integral with bifurcated extensions or arms attaching to the two bearings 28 surrounding shaft 26. This is required to permit lug 27 to form the central attachment to main cable 13 shown in Fig.4. The slit 30 is shown very narrow being only just wide enough to dear the towing cable 7. Periodically it will be necessary to replace the bearings in their housings that are integral with the arms extending from cable tube 29. For this purpose a detachable portion 31 of the cable float is provided of prismatic shape so that it can be withdrawn. Then the clamp 28 shown in Fig.4 can be loosened to permit shaft 26 to be removed followed by removal of the cables.

A modification of the arrangement shown provides simplification and allows greater accessibility to the bearings for maintenance. Instead of the cylindrical shaft 26 having is axis close to thc ccntrc of buoyancy it is pbced vcrtically below that point being mounted on a short strut fixed to the bottom of the cable float. Then the detachable portion 31 and the slit are eliminated with the cable float now being provided as a simpler single part.

Horizontal fins 32 can be optionally provided to ensure the cable float always presents the minimum frontal area to the direction of flow but these are not usually needed.

Referring now to Fig.6 showing athngitudinal elevation of an alternative form of cable float has externally mounted bearings. The cable float is drawn to the scale provided above.

This is the size needed to match an uppingvane of 12 metres span that has a positive buoyancy of 2/3 of the down force produced by towing at a speed of 2.5 metres per second.

This down-force is calculated to be 152,000 Newtons or 15.5 tonnes so the cable float together with 300 kilograms of cable has to provide 5.5 tonnes of buoyancy. Constructed largely from structural foam and with foam and seawater density taken into account a volume of 7 cubic metres has to be provided. A horizontal shaft having its axis perpendicular to towing cable 7 is located close to the centre of pressure of the cable float shown at the intersection of the two chain dotted lines. This shaft 26 also shown in Figs.7 and 8 carries the lift and drag forces due to the tension in main cable 13. The drag force of 19,330 Newtons carried by towing cable 7 is transmitted through two bearings positioned one on each side of the cable float so that they can make angular movement pivoted about the shaft. These bearings are fixed each to a bifurcated extension of cable tube 29A forming a pair of arms 29 made to match the external shape of the cable float with a small clearance. A Y member is formed by the cable tube 29A and arms 29. Cable tube 29A is made to fit around towing cable 7 fixed preferably by bronze welding. The upper end of the main cable 13 is fixed inside lug tube 12 that is locked into the cable float structure. The lug tube is made integral with a lug having a bore that is made a slide fit on the shaft 26.

The leading end of the cable float is formed as an arc whose centre coincides with that of shaft 26 so that a minimum of clearance can be maintained over a wide arc of movement of arms 29. This ensures that drag due to towing speed is minimised. Then as the angle between the two cables changes due to wave action it is the towing cable that moves relative to the longitudinal axis of the cable float.

A modification of the arrangement shown provides simplification and allows greater accessibility to the bearings for maintenance. Instead of the cylindrical shaft 26 having is axis close to the centre of buoyancy it is placed vertically below that point being mounted on a short strut fixed to the bottom of the cable float.

RefelTing now to Fig.7 showing a cross section on XX of the cable float shown in Fig.6 where more detail of the mechanism is provided. The cross section is shown to be deeper than it is wide and has sharp top and bottom edges 23 to minimise drag caused by vertical motion though these are not essential features. The cable float has a tough plastic shell 24 filled with structural foam 25 shown by the texture indicated. Such a structure provides adequate strength for withstanding pressure due to depth of operation at low cost. A hollow centre is provided for the coupling means between the two cables. A cylindrical metal shaft 26 has a horizontal axis that is also perpendicular to the towing cable 7 by fitting in bores provided in the cable float that are perpendicular to its long axis. Shaft 26 which can be hollow has a centrally mounted ug 27 damped over it and the main cable attaches to this lug by being fixed inside lug tube 12 made integral with the lug. Either side of this lug are two bearings 28 mounted at the trailing ends of arms 29 shown in Fig.6 that are positioned on shaft 26 close to the external surface 24 of the cable float. The bearings allow the towing cable vertical freedom of angular movement. Since the bearings are immersed in seawater it is preferred to use a bearing Uning that is water lubricated. Nylon has such a property and so offcrs a suitable material choice. The bearing housings made integral with aims 29 are split so that removable bearing caps are provided for replacement of bearings when maintenance is required.

A modification of the arrangement shown allows the rather large Y member represented by 29A and 29 to be reduced to a small size. histead of the cylindrical shaft 26 having is axis close to the centre of buoyancy it is placed vertically below that point being mounted on a short strut fixed to the bottom of the cable float.

Referring now to Fig.8 in which a sectional plan view is shown more detail is provided of bearings 28 and lug 27. The Y member formed by cable tube 29A and arms 29 is clearly shown. Cable tube 29A is shown in more detail to be integral with bifurcated arms 29 attaching to the two bearings 28 sulTounding shaft 26. What are shown as bearings at 28 are actually the bearing housings that are lined with replaceable linings that form the true bearings. These are located on cylindrical shaft 26 that has a horizontal axis that is also perpendicular to the towing direction. At the centre of shaft 26 lug 27 is located. The lug is a close fit on the shaft and has a radial extension subsequently split to form a clamp and has a hole for a clamping bolt. Lug 27 has a tububr extension called a lug tube 12 shown only in Fig.6 and Fig.7made a close fit around main cable 13 to which it is firmly fixed preferably by brazing. Since the lug tube is locked in place by structural foam neither the shaft nor the lug are able to move with respect to the cable float. Indeed this forms a complete unit that needs to be inserted in the mould before structural foam is injected. Several voids 33 are shown for minimising the cost of structural foam consequent upon the reduced volume of cable float required. These are provided by fixing inflated plastic balloons inside the mould used to produce the cable float. An important feature shown in this plan view is the shape of the Y member that is made to have only a small working clearance with respect to the cable float.

A modification of the arrangement shown allows the rather large Y member represented by 29A and 29 to be reduced to a small size. Instead of the cylindrical shaft 26 having is axis close to the centre of buoyancy it is placed vertically below that point being mounted on a short strut fixed to the bottom of the cable float.

Referring now to Fig.9 a mainly longitudinal section of a tug boat is shown to the vertical scale provided and is the same scale as that used for the cable float. The bow of the tug boat is shown at 1. A conventional tug boat can be utilised but the alternative shown has extra optional features that can be advantageous. One problem needing to be considered is the consequence of engine failure. Twin engines are often provided but the invention allows a single engine to be installed with alternative means for ensuring some propulsive power is available when the engine is shut down for maintenance. This provision is important since both cable float and uppingvane will then come to the surface but the weight of cables will then cause them to sink and pull all three components together. Then damage from wave induced collisions would ensue.

One such additional feature could be provided by a wind turbine. A design study provided the size of vertical axis wind turbine required to substitute for the 190 horse power diesel engine 46 operated at 60% of full load. At the conventional design wind speed of ii metres per second a rotor diameter and blade height both of 16 metres was required and seemed too large to be accommodated. A wind turbine having a horizontal axis needed the same frontal area and so offered no better a design solution. Therefore the size shown has only 3/16 of the frontal area desired for producing a power output of 82 kilowatts. Wind turbines never exceed utilisation greater that 30% and so the average wind power supplement could only be 5.6% of that required. However, if adopted despite this disappointingly low supplement a vertical axis turbine having four variable incidence blades 54 of the kind described in our Patent Application Number: GB 1208480.2 dated 15/05/2012 Ref: RDPO7 1210 can be provided by the invention. This has the feature of drag reducing the greater the wind speed exceeds the rated value. The blades 54 are carried by mounting struts fixed to rotating pylon 53. This pylon is fixed to the rotor 56 of an electrical generator. An electric transmission is provided to drive propeller S with most of the power being delivered from electric generator 47 attached to the output shaft of diesel engine 46. Antenna 2 is mounted at the top of pylon 53 now doubling as a mast for remote control to permit unmanned operation. If no wind turbine is incorporated then a mast is substituted for pylon 53.

Fuel tanks 48 occupy a large part of available hull internal volume and the engine would best be situated near the centre if no wind turbine is incorporated. Either electric or mechanical transmission can be provided. A suitable mechanical transmission is provided in the accompanying Patent Application Number 0Bl2l0097.0 my ref: RDPO5O6I2 flied 08/6/12.

A preferred means of providing auxiliary power is shown by the addition of hydrofoils 50 one positioned on each side of the hull as close as practicafly possible to the bow of the tug boat. Indeed the hydrofoils can with advantage be positioned at the end of a forward extension to amplify the vertical motion. In this way the invention is able to utilise wave power. In the North Sea waves are sometimes as high as 4.3 metres and are often of two metres height as indicated by the curve marked W. The bow of any boat in strong waves executes arge vertical oscillations and often a flared prow is incorporated to limit this motion. In the invention the hydrofoil provides the required damping by using the energy absorbed to supplement propulsion. Instead of a flared bow its transient submergence is permitted. The hydrofoils are of symmetrical section about their straight chord lines defined as connecting leading and trailing edges. They are arranged to pivot about a point 5i that colTesponds to the centreline of a horizontal shaft fixed inside the hull or its forward extension and perpendicular to its thngitudinal axis. Cylindrical bearings are provided inside each hydrofoil located on their centrelines between their centres of pressure 52 at stalling incidence and their leading edges. This ensures that their chord lines tend to line up with the direction of flow.

Means to be described are provided for ensuring the hydrofoil always operates with an angle of incidence that tends to produce a forwardly directed component of the lift force.

In this way not only a small towing force is provided with engine shut down but supplementary thrust is provided in strong wave conditions to offset the extra drag normally caused by waves.

Since each hydrofoil can experience different wave conditions especially when the hull is subjected to beam oriented waves the invention provides a means for their separate angirlar motions since they are mounted independently of each other.

The moment of inertia of a hydrofoil causes a phase lag as compared to the wave that is forcing its angular oscillation so this alone can provide the means required for producing wave power. A separate torsion dash pot is also optionally provided in the invention for each hydrofoil and each has a controllable resistance to motion in order to adjustably increase the phase lag. Each has a dashpot fixed inside the hull consisting of a casing that cooperates with a radial vane fixed to a cylindrical extension of the bearings inside each hydrofoil. The sides of the casing form a closed compartment that the radial vane divides into two chambers.

These are interconnected by a pipe containing a controllable valve which by adjustment allows the degree of damping to be adjusted. The internal spaces of both dashpots are filled

with suitable oil.

The invention also optionally provides torsion springs attached to the shafts and hull.

A hollow skeg 3 is provided attached to the bottom of the hull in order to provide a mounting for pod 4. This pod of circular cross section carries a centrally located propeller shaft to which propeller 5 is fixed. The opposite end of the propeller shaft has a driving means. The latter can be an electric motor. The propeller can be of shrouded kind as illustrated by duct 45 which surrounds the propeller with only a small clearance. Such ducts are known to provide greater thrust for a given diameter of propeller than when no duct is provided. Towing cable 7 is has eydet 6 attached to its leading end and a cooperating pin is attached to the pod 4 a short distance below the line of thrust shown chain dotted of propellerS. This is an optimum location that balances the moment of drag produced by the hull and its distance from the thrust line with the moment produced by the towing cable. This is not an essential option and the towing cable can alternatively be deployed from the hull.

A hinged rudder 49 is provided.

A novel form of hull construction is also optionally provided in the invention. Finite resources of metals including iron will become increasingly expensive owing to the increasing global expansion of their use. When marine farms become established for the sustainable production of the oil from which plastics can be sustainably produced it will be necessary to substitute plastics wherever possible. The hull shown is made of outer and inner shells having tough plastic skins 57 and 59 respectively with the inter space between them 58 filled with a structural foam. The main hull and deck components are produced using mounds lined with tough plastic that ultimately provide outer and inner surfaces after structural foam has been injected between them. A removable access hatch not shown is provided above the engine. In operation with hatch closed the completely watertight hull will be capaNe of operation under all adverse weather conditions.

RefelTing now to Fig. 10 an uppingvane whose leading end is at i5 is shown in longitudinal section taken at its centreline and is of hydrofoil shape having its more cambered surface as its bottom side. The lower end of main cable 13 has main eydet 33 cooperating with finks 14 that are attached by pivots to mountings 34 that are fixed to uppingvane 15 at a point slightly forward of where the centre of pressure occurs at stalling incidence. At reduced incidence the centre of pressure moves back so tending to cause the trailing edge to be pulled down. This is resisted by weak cable i6 attached close to the trailing edge to mounting 17. Then under all possible operating incidences that produce a down force the weak cable never slackens. Weak cable 16 attaches to the main cable at a position between eyelet 33 and the cable float by attachment to a sleeve 18 being a sliding fit over the main cable but having a longitudinal slit with flanges provided for a clamping bolt. This enables operating incidence to be adjusted.

Indeed the sleeve can be provided without a slit and damping boll but with a weak cable extension attached at the cable float whereby incidence can be controlled during normal operation.

Any link 14 is of such length that its upper end can reach beyond the nose 15 when rotated to lie as flat as possible along the upper surface of the uppingvane. The link may be curved so that its now forward end can come as close as possible to a ring 47. This enables a clamp to be provided passing through the ring and over the now upper side of the link to clamp it in position. This condition is then suitable for towing in shallow water and to the site where it is to be deployed.

The uppingvane 15 is shown with an outer plastic skin 36 filled with structural foam 37 that also provides most of the structural stability. Reinforcement is provided by two steel sheets. Upper sheet 38 is in tension with lower sheet 39 in compression so the pair forms a main spar with shear stresses taken by the intervening structural foam. If necessary these two sheets can be joined by vertical sheets to form a box spar. The mountings 34 for the links and mounting 17 for the weak cable 16 attach directly to upper sheet 38 preferably by welding.

Therefore to provide the required structure both sheets have axial extensions 46 (shown only in fig. 11) tapcring rcarwards almost to thc trailing edge. Fins 22 arc fixcd one to each tip arc provided close to the straight trailing edge of the uppingvane. These fins provide weathercock stability. Uppingvanes tend to have excessive buoyancy when completely filled with structural foam. To reduce this to an acceptable value ballast 40 is provided and can be placed at any suitable position. The cheapest possible material such as concrete can be used for ballast.

When a weak cable is provided the position of ballast can be at any point along the centreline (43 of the uppingvane shown in Fig. 11) between leading and trailing edges. A stable incidence can be provided by alternative means such as by elevators at the trailing edge or winglets near the leading edge.

With elevators at the trailing edge it is preferable to have one placed each side of the centreline and separately controlled so that both lateral as well as longitudinal stability can be provided. In this case main cable i3 extends to a single eyelet located on the centreline with links 14 and weak cable 16 omitted. All cases where dynamical stability of such kind is provided the position of ballast is critical and needs placing near the leading edge.

The horizontal direction is indicated by chain dashed line H and the arrows on it indicate the direction of flow relative to the uppingvane at design incidence. The chain dashed line V indicates the vertical direction. If the uppingvane had neutral buoyancy then line 44 indicates the position of the main cable 13. With uppingvane buoyancy able to reduce the vertical component of cable force to 1/3 of hydrodynamically induced down force the cable position would be as indicated by fine 45 and this corresponds with that shown in Fig. I. As shown by 13 the cable position corresponds to a reduction of cable force to 1/6 of this down force and suggests that the buoyancy of the uppingvane is then too big.

RefelTing now to Fig. II showing a plan view of the uppingvane a straight trailing edge 41 is provided with tip sections having on'y a small fraction of the chord provided at its centreline.

The rounded leading edges 42 are straight but are at an angie of about 90 degrees to each other as dictated by the difference in chord from centreline to tip. Fins 22 attach to each tip and are of thin symmetrical hydrofoil section with their chord lines parallel to the centreline 43 of the uppingvane. The reinforcing sheets 38 and 39 foim the main spar and are shown in plan view tapering from centreline to tips being swept back so the included angle between the two leading edges of these sheets is less than the included angle between the two eading edges. Both sheets have rearward extensions 46 that taper toward the trailing edge 41. The main mountings 34 and trailing mounting 17 are fixed to the upper sheet 38.

RefelTing now to Fig. 12 showing a frontal view of an uppingvane the two links 14 join the uppermost steel sheet 38 inside the uppingvane at positions equidistant from its centreline in order to provide lateral stability. The weak cable 16 is attached to a point near the trailing edge by a horizontal pin passing through eyelet 35 and is on the centreline of the uppingvane.

Main cable 13 is attached to the two links 14 by an eyelet fixed to the end of main towing cable 13 by a pin 33, Weathercock stability is provided by the two fins 22 located as close to the straight trailing edge of the uppingvane as possible and are attached at an obtuse angle to the horizontal so that they extend below the bottom surface of the uppingvane RefelTing now to Fig. 13 a thngitudinal section on YY of Fig.. 14 of a cable float is shown having fixed within its internal structural foam 25 a spar 60 provides a cable connection. The cable float has a tough outer plastic skin 24 and optional voids 33 produced by air filled bags during the foam tilling procedure. Towing cable 7 is brazed inside towing tube 29A that terminates in a bifurcation to form a Y piece in which the arms of the Y have bores for bearings or form an eyelet of substantially larger internal diameter than the cooperating cylindrical shaft so that it can pivot without sliding being involved. A central lug can also have a similar large bore to enable it to pivot when cooperating with the same shaft or can be a clamp lock it in position. The lug is integral with main cable tube 12 into which main cable 13 is brazed. In this way the cables can make free angular movements to accommodate large waves.

RefelTing now to Fig. 14 a cross section on XX of Fig. 13 of a cable float is shown in which spar 60 is shown bifurcating into two arms 61 having bores to accommodate cylindncal shaft 26. Centrally located on this shaft is lug 27 that can be either a clamp to lock it onto the shaft or it can be an eyelet of larger bore than the diameter of the shaft in order to provide a pivot.

This lug or eyelet is integral with main cable tube 12 into which main cable 13 is brazed. The towing cable tube 29A shown in Fig.13 bifurcates into arms 28 bored to form eyelets one on either side of lug 27 to provide a pivot for the towing cable or bores 28 can be bearing housings.

RefelTing now to F 1g. 15 a plan section of an uppingvane taken through the space 67 of the auto stabilising elevator is shown. This view looks down onto the thin metal dividing sheet 64 shown in Fig. 16. Tube 62 connects with space 67 to form a hermetically sealed chamber containing a dense fluid such as tetrabromoethane. Tube 62 terminates at a bellows 71 situated as close as possible to the nose or leading end of the uppingvane and the end flange of the bellows connects through a rod to an actuator or servomechanism 73. This is actuated by current from an electnc cable attached to both main and towing cables to a control mans provided in the tug boat. When this rod is partially withdrawn the elevator is deflected upwards to increase incidence and pushed in to reduce incidence. The bellows 71 is contained in chamber 72 having a short pipe opening to the sea at a port 74 placed at any suitable arbitrary position. This chamber 72 also connects with pipe 63 that opens below dividing sheet 64 to the space below the elevator whose trailing edge is 41. This pipe 62 and the space below dividing sheet 64 is filled with seawater.

Referring now to Fig. 16 a cross section of the elevator of an uppingvane is shown in a vertical plane to a larger scale than Fig. 15. The horizontal metal dividing sheet 64 separates the upper chamber 67 containing a dense fluid from the lower chamber 69 containing seawater, Sheet 64 is built into solid material situated opposite trailing edge 41 near space 65.

Outer surfaces 36 are bonded to this material and cover the remainder of the uppingvane that is at least pardy filled with structural foam 37. Spaces 65 and 68 can have quite large cross sectional area in order not to impede the flow of fluid contained in these chambers 67 and 69.

The outer upper surface 66 and outer lower surface 70 of the elevator are made from a flexible material such as rubber and have vertical walls at intervals along the span that are bonded to dividing sheet 64. 1-loles can be provided in these vertical walls to provide extra areas for the flow of fluid. k this way pressure differences between upper and lower chambers cause small transient flows of the contained fluids to cause the elevator to deflect.

Auto stabilisation to provide operation at the desired incidence is provided by pressure differentials produced by the two fluids when level at the training edge changes with respect to that at the centre of bellows 72. When negative incidence increases the devator is bent upwards to force the trailing edge down and when one tip near fins 22 rises up with that opposite moving down the elevator twists to act as a pair of ailerons to correct that banking motion.

Claims (9)

1. CLAIMSi An apparatus consisting of a tug boat connecting with a cable float by a towing cable and with the cable float connecting by a main cable with a hydrofoil operated with its eading edge lower than its trailing edge in order to project seawater containing the nutrients needed for the growth of marine plants toward the surface of the sea and in which the cable float when fufly submerged is able to support the difference in force between the net down force produced by the difference between the inverted lift of the hydrofoil and its buoyancy so that an obtuse angle exists between the towing cable and the main cable so that waves cause a variation of this obtuse angle so substantially preventing the wave induced motion of the tug boat from being transmitted to the hydrofoil.
2. 2 An apparatus as claimed in claim 1 wherein the cable float has a horizontal cylindrical shaft arranged perpendicular to the towing cable this shaft being fixed close to its ends by cooperating clamps that are rigidly attached to the cable float in such a position that the line of action of the resultant force it caries passes close to the centre of buoyancy of the cable float and on this shaft a centrally located lug is clamped this lug having a main tubular extension that encloses and is fixed to the main cable and in which two bearings cooperating with the shaft are provided one on each side of this lug that permit angular motion about the shaft each of the two bearings being fitted inside an arm the two arms joining at a single towing tube inside which the towing cable is fixed.
3. 3 An apparatus as claimed in claim 2 wherein the cylindrical shaft is located close to the centre of buoyancy of the cable float and extends outside its surface each protruding end of this shaft cooperating with a bearing fixed into an arm and in which the two arms that are also outside the cable float join at a towing cable tube into which the towing cable is fixed.
4. 4 An apparatus as claimed in claim 2 wherein a spar extends from the bottom surface of the cable float and close to the bottom end of this spar it bifurcates into two members that have cooperating bores that can be made as clamps to support the said horizontal shaft that also carries a central lug attaching to the main cable with a bearing on either side that connect with the towing cable the horizontal shaft being removable after releasing the clamps.
5. An apparatus as claimed in claim 2 to claim 4 wherein the cable float is provided with eyelets instead of bearings and lug the internal diameter of the eyelets being substantially greater than that of the cooperating cylindrical shaft so that a rocking motion occurs free from the sliding that arises when bearings are provided.
6. 6 An apparatus as claimed in claim 1 wherein the cable float has a horizontal shaft of arbitrary cross sectional shape also arranged perpendicular to the towing cable this shaft being fixed below the centre of buoyancy of the cable float on a spar to place this shaft below the cable float and rigidly fixed to this shaft are three sheets that are wide in the direction parallel to the shaft axis but thin in the direction transverse to that axis and are made from spring steel so that they all form flat springs and in which the outer springs form arms that join at a towing tube into which the towing cable is fixed and in which the central sheet is integral with a main cable tube into which the main cable is fixed so that bending of these springs permits the obtuse angle between the two cables to vary without any sliding parts being required.
7. 7 An apparatus as claimed in claim 1 wherein the cable float consists mainly of structural foam and is produced by the injection of foam into a mould lined with plastic that forms it outer suitace.
8. 8 An apparatus as claimed in claim I wherein the hydrofoil has a chord at mid span much greater than the chord at its tips the hydrofoil having a straight trailing edge and at the tips vanes are provided that make an obtuse angle less than 150 degrees measured from the underside of the hydrofoil to provide stability in the direction of travel.
9. 9 An apparatus as claimed in claim 8 wherein the lower surface of the hydrofoil is more cambered than the upper surface and the hydrofoil is towed with its leading edge at a lower level in the sea than its trailing edge.An apparatus as claimed in claim 8 and claim 9 wherein the hydrofoil has at least one link to which the main cable is attached by an eyelet fixed to the bottom end of the main cable and has a pin passing through eyelet and link in which any link is attached to a mounting bracket fixed close to the upper surface of the hydrofoil at least distant from the leading end or nose by an amount that p'aces it dose to the centre of pressure at stalling incidence.ii An apparatus as claimed in claim 10 wherein the hydrofoil has two links that touch at their upper ends where the main cable is attached by an eyelet cooperating with a pin that passes through both links and eyelet and wherein the lower ends of the links are separated to be attached to the hydrofoil by two separate mounting brackets so that lateral stability is provided.12 An apparatus as claimed in claims 10 and 11 wherein and the link is of sufficient length as to extend beyond the nose when placed in a surface towing mode of operation when it is clamped in position to a nose ring fixed to the nose of the hydrofoil.13 An apparatus as claimed in claim 8 and 9 wherein a weak cable is provided for controlling the incidence of the hydrofoil the weak cable being attached at its bottom end at mid span and close to the trailing edge of the hydrofoil and at its upper end is fixed to a sleeve that surrounds the main cable and is provided with a clamping bolt so that its positionis made adjustable.14 An apparatus as claimed in claims 8 and 9 wherein longitudinal stability is provided by at least one elevator attached to the trailing edge of the hydrofoil and an actuator of some kind is connected to any elevator such that any undesired change of incidence is corrected and in which no weak cable is provided and in which ballast is provided to locate the centre of gravity close to the centre of pressure at operating incidence.An apparatus as claimed in claim 14 wherein an actuator consists of a bellows having an end plate close to the nose of the hydrofoil the bellows being open at its other end to a tube which in turn connects with an upper chamber of an elevator the combination being completely seakd and filled with a dense fluid having a density several times that of seawater wherein the elevator is divided by a thin metal sheet into upper and lower chambers the latter filled with seawater and connecting with another tube terminating in a containing chamber surrounding the bellows that containing chamber connecting with a tube terminating in a port open to the sea outside so that as the elevator nses the pressure in its upper chamber falls more than that in the lower chamber so producing a colTecting deflection of the elevator and since the elevator can twist up on one side and down on the other the trailing edge of the hydrofoil is maintained horizontal as well as maintaining the required incidence.16 An apparatus as claimed in claim 15 wherein an actuator rod is provided that connects with the end plate of the bellows so that by an axial displacement of the actuator rod an elevator can be adjusted to control the incidence at which the hydrofoil operates with the stabilising contr& by the means provided in claim 15 being retained.17 An apparatus as claimed in claim 16 wherein a servomechanism is provided cooperating with the actuator rod for controlling its axial position the servomechanism being in electrical connection to the tug boat for enabling the incidence at which the hydrofoil operates to be remotely controlled.18 An apparatus as claimed in claim 17 wherein two elevators of the kind described are provided equally disposed one on each side of the centreline of the hydrofoil and in which each has a separate bellows actuator rod and servomechanism both enclosed in the same containing chamber that connects with both lower chambers of the elevators so that the elevators can also act as ailerons to permit banked turns noting that when only a single elevator is provided it only acts as ailerons to eliminate any lateral displacement from the horizontal.19 An apparatus as claimed in claim I or 15 wherein the hydrofoil is mainly constructed from structural foam but having external surfaces of a tough plastic and containing metal sheets to form the main spar the structure and ballast and any other components the hydrofoil being made by the injection of structural foam into a mould.An apparatus as claimed in claim 1 wherein the tug boat has a pair of hydrofoils of symmetrical section mounted on a horizontal shaft whose axis is perpendicular to the centrëline of the hull near its bow or on an extension to the bow with the hydrofoils mounted on that shaft in cooperating bearings within them and positioned with their axes on their centrelines and located between their leading edges and the centre of pressure of the hydrofoils at stalling incidence so that wave induced motions cause the hydrofoils to operate with an incidence to the flow that produces a forward thrust whether moving up or down relative to the seawater.21 An apparatus as claimed in claim 20 wherein the tug boat has a pair of dash pots with valves to vary the damping provided connecting the hydrofoils to the hull in order to control the incidence at which the hydrofoils meet the relative flow.22 An apparatus as claimed in claim I wherein the tug boat has a towing cable attaching means ocated on a pod or skeg bdow the axis of a propeller.23 An apparatus as claimed in claim 1 wherein the tug boat is at least partly powered by a wind turbine mechanically connected to an alternator and in which an engine is also provided having an alternator connected to its output shaft and in which both alternators are electrically connected to an electric motor that drives a propeller.24 An apparatus as claimed in claim 1 wherein the tug boat has a hull largely made from structural foam with outer and inner skins made from a tough plastic the component being formed in a mould made from a cheap material such as concrete.