GB2497611A - Motor powered upwelling apparatus for ocean cultivation to generate food and fuel with carbon sequestration - Google Patents

Abstract

A motor driven tug boat tows an inverted hydrofoil 17 at a depth of 60 metres in the North Sea to bring up nutrient rich seawater to the photic zone at the surface. The hydrofoil is towed by means of a cable 19 that may be deployed from a winding drum 18. Phytoplankton proliferate at the surface boosting fish stocks and cultivating floating varieties of seaweed that reproduce by vegetative means. When converted to fuels like natural gas only about 5% of the extracted energy needs to be re-invested for operating the system. The result is to provide a source of sustainable alternative energy that also reduces acidification of the ocean and provides a means for sucking carbon dioxide back from the air.

Description

MOTOR POWERED UPWELLING APPARATUS FOR OCEAN CULTIVATION TO

GENERATE FOOD AND FUEL WITH CARBON SEQUESTRATION

1 Ronald Denzil Pearson of 2 Rowlands Close Bathford Bath BA I 7TZ hereby apply for a patent that 1 hope will be granted.

This patent application covers different apparatus from that described in:

WIND POWERED UPWELLING SHIP FOR OCEAN CULTIVATION TO

GENERATE FOOD AND FUEL WITH CARBON SEQUESTRATION

This has the Patent Application Number: GB 1208480.2 dated i510512012 Ref: R1W071210 The present application has the same purpose of ocean cultivation as the above but does not utilise wind power. Instead some form of prime mover such as an engine needing fuel provides the motive power. This alternative has the advantage of doubling utilisation and so could be more economically viable even when there is a fuel demand. The motor powered cultivator would only consume by way of example and not limiting in any way less than about 5 percent of the product if a farmed area of the North Sea included a floating seaweed crop that is harvested for conversion to natural gas. The previous wind powered ocean cultivator may be the best choice until the farmed area is large enough to introduce floating varieties of seaweed to provide the major crop.

Initial application in the North Sea is desirable since quite small apparatus is adequate and violent storms can develop that provide the required test conditions for ensuring adequate reliability. For adequate mitigation of environmental problems such as global warming and the reduction of ocean acidification much larger sizes of apparatus will be required for deployment in the deep oceans. Also a greater proportion of the energy produced will then need to be sacrificed since the nutrients required to promote the growth of algae have to be extracted from depths about five times as great as in the North Sea.

The present invention provides a small tug boat driven by a prime mover such as an internal combustion engine or motor that allows an inverted hydrofoil that is to be called an uppingvane to be towed. The motor could be an electric motor. For example it could operate from a fuel cell. The uppingvane forces seawater to rise from depths of 50 to 60 metres to the surface in the North Sea. This seawater contains the nutrients essential for the growth of marine algae. What a computer simulation has predicted is that the result will be between a doubling and trebling of fish stocks together with about half the biomass produced as seaweed. This is a selected floating variety such as Sargassum natans or muticurn that reproduce vegetatively so not requiring anchorage to rocks or sea bed. Ultimately the invention could be applied for cultivation of oceanic gyres in the deep oceans to provide a solution to major global problems of present concern though much larger apparatus will then be required since seawater then needs to be brought from depths of about 300 metres.

Floating seaweed is relatively easy to harvest and can be anaerobically digested to produce natural gas. When this is burned carbon dioxide is released to the atmosphere to enhance the unwanted greenhouse effect. However this gas was absorbed from near the surface of the sea in the first place so enhancing its ability to reabsorb that gas. The air and sea will be maintained out of equilibrium so that the increase of acidification of the ocean now a cause for concern will be diminished or alTested and if energy from cultivating oceans replaces the burning of fossil fuels the concentration of CO2 in the atmosphere will be stopped from increasing. The effect will be enhanced by the production of phytoplankton. These micro organisms are eaten by harvestable fish to result in further carbon sequestration. In this way the invention provides a means for solving a number of environmental problems and on a

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worthwhile scale. This is made possible since the environmental benefits are provided as a by product of a commercially viable solution for the provision of sustainable alternative energy products at a reasonable cost.

Background information is provided in Patent Application Number: 0B1208480.2 dated 15/05/2012. This will not be repeated but instead a short summary follows next.

The previous application describes how the ocean and the North Sea in particular can be cultivated by moving seawater from depths below the photic zone almost to the surface of the sea using wind power. At the depths of interest al the nutrients exist in concentrations that are adequate for the growth of marine plants such as the single celled phytoplankton and some floating varieties of seaweed. Productivity during the growing season is limited by the slow rate of diffusion of these nutrients to the surface. Consequently there is a spring bloom followed by very little productivity during the summer. By accelerating the process using artificial upwelling productivity over the entire growing season can be more than doubled.

Phytopankton form the base of the food web that leads to harvestaNe fish and so the fish stocks now under threat from over fishing can be revived. Furthermore the increased productivity will change the concentration of inorganic carbon in the sea in such a way as to cause more carbon dioxide to be absorbed from the atmosphere. Some is sequested on the seatloor with the rest swept into the Atlantic Ocean. In this way the sequestration of carbon dioxide is achieved as a by product of the operation and can be largely or competdy funded by the carbon credits for which the operation will be eligible.

When a sufficient area of the sea has been placed under cultivation another kind of crop can be introduced. Floating varieties of seaweed are known such as Sargassum fluitans S. natans and S. muticum that reproduce by vegetative means. These are readily harvestable and can be converted to natural gas by anaerobic digestion or to a form of crude oil by heating at high pressure. In this way a means for an indefinitely sustainable energy source can be created in which a net sequestration of carbon dioxide is also provided. And this sequestration is intimately connected with the increase of fish stocks that will also happen.

The net sequestration is due to the phytoplankton since only about half the productivity will appear as seaweed. Fortunately from the process of anaerobic digestion used for the conversion of seaweed into natural gas all nutrients can be recovered for recyde. Then the cultivated area can be approximately doubled so that about the same amount of natural gas can become available as calculated for the case of none lost to phytoplankton production and no recycle. These floating seaweeds can also provide an indefinitely sustainable source of chemicals and a feedstock from which materiak such as plastics can be produced.

Furthermore the cultivation of the North Sea followed by parts of the deep oceans of the world can be carried out without any artificial confinement by anchored barriers or nets so that other shipping is not prevented from navigation through the cultivated areas.

There are eight oceanic gyres and these offer particularly favourable locations for farming the open ocean. This is because of the natural confinement of the floating crop by circulating currents.

My invention is a tug boat containing at least one prime mover that can for example be a motor or internal combustion engine that connects with a power transmission including a speed reducing means to at least one large propeller and in which a cable deployed from the hull or the equivalent is attached to a hydrofoil that is towed underneath the hull so that a downward component of force is produced on the cable. When the prime mover is a motor it could be for example an electric motor. This could be connected to a fuel cell.

A steam turbine operated from steam generated from seaweed being dried is not a motor or prime mover according to the definitions used in this invention.

The hydrofoil deployed in this way is to be called an uppingvane and is to be operated at a suitable depth in such a way that it produces a vertically downward lift force in order to deflect a plume of seawater toward the surface of the sea in which the plume contains a much higher concentration of the nutrients required for the growth of marine p'ants than exists at the surface during the growing season. For this purpose the uppingvane has to move horizontally with its leading end at a lower level than its trailing end.

As will be proved mathematically later in this specitication an uppingvane has remarkaNe potential for cheaply fertilizing the ocean. Computations show that the energy potential in the biomass produced can exceed 400 times the energy needed to tow the uppingvane when towing energy is defined as the drag force at the uppingvane inclusive of induced drag and skin friction multiplied by towing speed.

For the kind of embodiment of the invention that needs to be introduced for operation in the North Sea or open ocean the prime mover is fixed inside the hull of a tug boat and the uppingvane is deployed at a suitable depth being towed preferably on a cable. The front of any boat is its bow so in front means toward the bow. Any propeller is preferably though not essentially fixed at a point in front of the point at which the cable is deployed to minimise the risk of fouling of any propeller by the cable. Any propeller is oriented as close to a horizontal axis as possible by mounting it on bearings inside a pod that in tum is supported by a streamlined strut known as a skeg attached to the hull. In order to provide the very high thrust at the low forward speeds required the area to be called an actuator disc is usually greater than the underwater frontal area of the hull required for providing the buoyancy needed to counter the downward component of force caused by the cable and the weight of material comprising the hull and machinery it carries. This provides another important feature of the invention since no prior art has such a feature. An actuator disc is defined here as the area AAC:J swept out by the propeller Nades given by the equation: AcT = 0.7854X(D2 -Dm2): DT = tip dia.: = hub dia.

Although very large propellers are provided they operate with relatively low speeds through the sea and so are not required to be very strong and heavy. Fabricated structures from sheet metal and/or plastic are suitable. A problem with all propellers arises due to the pressure difference created by motion on opposite sides of each blade. This causes an unwanted flow over the blade tips and results in tip vortices that waste energy and reduce propulsive thrust.

In a preferred embodiment a shroud is fixed to the tip of each blade to reduce this unwanted effect. Each blade tip is in the form of an arc centred on the axis of rotation and the shroud is made in an arc of the same curvature fixed to the blade tip extending from blade leading edge to blade trailing edge and forming part of a cylindrical surface.

In a preferred embodiment of the invention a winding drum is provided about which the cable is wrapped and in which the other end of the cable is attached to the uppingvane. The uppingvane is preferably but not essentiaily a hollow structure having positive buoyancy but is pulled down to working depth by forward motion of the hull, It rises back to the surface when motion stops. It is a hydrofoil as viewed in longitudinal section and can be symmetrical or have a more cambered surface on its underside. It has a low aspect ratio defined as span squared divided by plan area a typical va'ue being 3. The plan form can have any shape from a delta shape though a half ellipse to a rectangle. In a preferred embodiment the trailing edge is a straight line but this is not an essential feature.

Since the structure of the uppingvane will be subjected to an external high pressure when at operating depth a suitable constructional material is steel reinforced concrete.

Reinforcement is only required near the upper surface. To achieve slightly positive buoyancy internal voids need to be provided. An alternative is a strong plastic shell filled internaHy with structural foam. In either case very cheap manufacture is promised.

When towed with forward end lower than trailing end seawater is propelled both upwards and to a much lesser extent forwards foflowing the hull in a plume known as a Rankine oval that moves as a body separately from its sulTounding seawater. Its internal structure is a vortex pair in which the speed of rotation increases as distance from the vortex centres is reduced. High speed vortex cores result that produce high drag. This drag penalty can optionally be reduced by the application of a set of winglets as descnbed in patent specification number G B09052 13.5 dated 26/3/2009.

The point of attachment of the cable is arranged close to the centre of pressure of the uppingvane. hi the simplest embodiment the angle of incidence is fixed by the accurate positioning of the point of attachment using an eyelet on the lower end of the cable to cooperate with a horizontal pin mounted in a bracket fixed to the upper surface of the uppingvane. For a more accurate fixation of incidence the eyelet is attached to a so called delta bar consisting of rigid bar of streamlined section having two legs that form a triangle with the junction of the two legs forming an apex where the eyelet of the uppingvane cable attaches whilst the base of the triangle lays along the centreline of the uppingvane. In one embodiment of the invention the uppingvane is allowed to rise and fall with the tug boat due to wave effects. To mmmli se variation of tension in the cable the inclination from the horizontal direction of the uppingvane is made variable so that almost a constant incidence to the relative flow of seawater is maintained. Several means are provided by the invention. One simple means has the rearward leg of the delta bar made flexible for example by use of a material of low modulus of elasticity or by adding a spring. Then when tension is increased due to the tug being lifted by a wave the rear leg extends to reduce the difference in depth between leading and trailing edges whereby incidence and therefore force increase on the cable is reduced. The leg of the delta bar nearest the leading edge of the uppingvane is attached by a hinge to the upper surface of the uppingvane but the other and rearward leg is preferably though not necessarily attached close to the underside of the uppingvane so that a coiled or flat spring can be provided within the uppingvane.

The uppingvane cable is made preferably of high tensile steel wires and has a plastic wrapping that also forms a streamline cross section. The streamlining extension can be loose fitting and made in short sections so that they always line up with the direction of motion.

Strong wave action will be experienced from time to time and will overstress both cable and uppingvane main spar unless further countermeasures are taken. The invention provides appropnate apparatus that will minimise wave induced stress variation. The uppingvane winding drum has a coaxial shaft mounted on bearings fixed to the hull so that this shaft has a horizontal axis and has a spur gear fixed to it at a convenient position. Either an electric motor or a hydraulic motor is provided that is mechanically coupled to the spur gear so that the uppingvane can be raised or lowered. The hydraulic drive is the preferred option since it is more suited for operation in conditions when there are high waves. A gear motor also able to act as a gear pump will be called a gear pump/motor and has a pinion mounted on the same shaft as one of its two internal gears to cooperate with the spur gear connecting with the winding drum either directly or through a further reduction gear. One port of the gear pump/motor connects by a pipe to an oil reservoir that can be at atmospheric pressure or an accumulator operated at not many times atmospheric pressure. The other port of the gear pump/motor connects by second pipe to a high pressure accumulator which also connects by a third pipe to a gear pump dnven from the prime mover with a clutch interposed. By this means the accumulator can be filled until the pressure is sufficient to balance the force on the cable. Then when the hull is oscillating due to waves the force on the cable is maintained almost constant with the drum winding and unwinding with oil flowing into or out of the accumulator without any valves being required. For adjustment of the depth of deployment of the uppingvane the pressure inside the accumulator needs to be changed.

When this pressure is increased the gear pump/motor acts as a motor to wind in the cable against the downward force produced by the uppingvane. This requirement determines which port of the gear pump! motor needs connection to the accumulator. The power and oil flow needed is provided by the gear pump by closing the clutch connecting with the engine. For letting out cable the gear pump/motor acts as a pump producing an oil flow to the accumulator. A dump pipe containing a valve is provided for returning oil to the oil reservoir to allow the process to continue.

It is possible to have a more complex arrangement that enables wave power to be harnessed. Then two accumulators are provided operating at different pressures and both are connected to the high pressure port of the gear pump/motor by pipes containing non return valves. The highest pressure accumulator is thereby not allowed outflow and the lower pressure accumulator not allowed inflow. In this way wave induced vertical motion causes oil to be pumped from the lower to the higher pressure accumulator. A gear motor is also provided connected by piping to both accumulators and having its output shaft connected to any other apparatus needing power. Analysis suggests however that the power supplement may be too small to be economically viable. This description will subsequently be regarded as applying to the uppingvane cable associated with an uppingvane winding drum since in a preferred embodiment of the invention another cable is also provided for towing a recycle bag.

Whatever shape of plan form of uppingvane is selected in each case a bending moment caused by the force on the uppingvane cable needs to be resisted and a main spar of preferably high carbon steel can be provided. The uppingvane need not be constructed entirely of metal and can even be made with very little metal. It can be constructed of reinforced concrete with most of the reinforcement close to the upper surface which is in tension. It preferably contains adequate voids in order to ensure it has small positive buoyancy. Alternatively an uppingvane can have a strong plastic skin with the interior filled with structural foam. Some concrete ballast can optionally be included to counter any excessive buoyancy. By such means very cheap construction is achievable.

Another means of preventing excessive forces being applied to the uppingvane cable during high wave conditions is provided by the invention that can be used instead of or in addition to that already described. The main hull is made to have minimum buoyancy so that the force on the uppingvane cable is able to cause submergence. A vertically oriented prism of streamline plan form and of relatively small cross sectional area is provided to be called a conning tower. This is attached to a central and upper part of the main hull so that the conning tower protrudes above the surface during normal operation. The combination of main hull and conning tower comprises the hull.

The apparatus can be operated as a robot so that no crew is required or it can have a crew. For manned versions of the invention a bridge is located at the top of the conning tower. The degree of submergence is controlled by varying power output from the prime mover. Increase of power increases speed and down force from the uppingvane so increasing the degree of submergence. Intake and exhaust pipes when fitted are provided that have openings to the atmosphere at a high enough level to prevent the ingestion of seawater. The main hull is preferably of circular or octagonal cross section as viewed from the direction of motion in order to minimise structural weight and yet counter the external pressure taking into account the depth of several metres at which it is designed to operate. This cross section can only apply to about two thirds of the distance from the bow since the two vertical plates of the hull are maintained of constant width with the remainder tapering to near zero width at the stern in order to provide a hinge joint on which a rudder is mounted.

A mast is provided that is attached to the conning tower. At the top of this mast navigation lights and a radio antenna are provided the latter being required for positional control.

In order to prevent seawater entering the main hull when operating submerged when the uppingvane cable drum is mounted in the main hull internal pressurisation is required.

This is also desirable since the thickness of the hull material is also then minimised. If a turbocharged diesel engine is the prime mover then the air delivered from the compressor of the turbocharger can be delivered into the hull and the internal surface of the hull used as the aftercooler by arranging fans to circulate the air inside the main hull. The air intake port of the engine is then open to the interior of the hull.

Some typical figures will be quoted in the following description but these are to be considered as not limiting and are provided by way of example only.

Power transmission from prime mover to at least one propeller has to include means for a very large speed reduction that can typically be about 35 to one. Three alternatives can be incorporated in the invention.

A mechanical transmission is one embodiment. To incorporate an engine of known kind having a horizontal output shaft a bevel pinion is fixed to a clutch cooperating with that output shaft this pinion meshing with a crown wheel to form a first stage reduction gear of about 7 to 1 ratio. The crown wheel is fixed to a vertical shaft having another bevel pinion fixed to its bottom end and meshing with a very large crown wheel fixed to a horizontal propeller shaft. This forms a second stage reduction gear of about 5 to I ratio so that an engine operating at 2000 revolutions per minute can drive a propeller spinning at only about 57 revolutions per minute. The vertical shaft is contained within a skeg and the pod attaching to the skeg and in which the propeller shaft is coaxially mounted has to be about 0.3 of the tip diameter of the propeller in order to accommodate the very large crown wheel.

A hydraulic transmission has the advantages of compactness but has an efficiency of only about 75 percent as compared to a mechanical efficiency of about 96 percent applicable to the previous case. Therefore this altemative is not adopted.

However an electric transmission can be provided that promises a satisfactory alternative. In this case in one embodiment a generator mounted on the output shaft of the prime mover supplies electric current to motors having pinions meshing with the spur gear fixed to the propeller shaft.

A preferred embodiment of the invention with electric transmission incorporates a tip driven propeller. Tip driven propellers are known that are operated by electric transmission and are said to be more efficient than those coupling with the propeller shaft. Indeed in such transmissions no propeller shaft or gears are incorporated. An alternator is coupled directly to the output shaft of the prime mover. The propeller has fully shrouded blades meaning that a short cylindrical ring is attached to all blade tips. This ring has a multiplicity of permanent magnets fixed to its outside surface and these cooperate with coils fixed to an enclosing ring that in turn is fixed to the bottom of the hull. These coils connect to the alternator to provide the equivalent of a reduction gear.

Very large propellers produce a consideraNe reaction torque. To cancel this any skeg that is attached to the hull and a propeller pod is positioned behind the propeller and has a hydrofoil section so that it acts as a stator to remove vortex motion of the seawater. Near the propeller hub the speed of the vortex is much higher than at greater radius and so the skeg is preferably constructed with a high camber close to the hub. Indeed the skeg is formed into a converter of vorticity to pressure rise as in the stators of axial air compressors. To further this end a skeg extension is provided which extends from the underside of the pod to a slightly lower level than is reached by the propeller in order to provide adequate removal of the vortex and this also will be cambered at least close to the pod which is a streamline shape cooperating with the propeller hub. A pair of horizontally oriented vanes can optionally be incorporated extending laterally from the pod though not extending to as great a radius as the propeller blade tips.

In a preferred embodiment that can be provided when one or other odd number of propellers are incorporated the uppingvane cable is passed through the skeg that is fixed to the centreline of the hull the pod and skeg extension. A curved cable guide is provided extending from the rear and bottom open end of the skeg in order to prevent an excessively small radius of curvature of the cable from developing. The cable is confined within a separate cable compartment or tube within the skeg to prevent seawater reaching any reduction gears. A small low pressure air compressor can be provided to pressurise the hull so that the water level is maintained within the cable compartment and prevented from entenng the main hull. This internal pressurisation also minirnises compressive stresses in the main hull and so permits the use of thinner steel plate than would be required without internal pressurisation. Alternatively the winding drum can be located well above sea level in the conning tower.

if the fuel tank is to be refilled as part of the engine servicing routine that normally takes place about every 500 hours then for continuous operation this means every 21 days. This quantity of fuel can be greater than the entire weight of material from which the tug alone is constructed. For the minimum buoyancy principle on which the tug design is based the removal of so much fuel would have the undesirable consequence of causing the main hull to become excessively buoyant. To prevent this alternative compensation measures are provided in the invention and both require an increase in length of the main hull. One provides sets of flexible water bags inside the large fuel tanks that have their external surfaces in contact with the fuel oil and when the tanks a full these bags flatten so that little space is occupied. The bags have pipes attached that are open to a bag at one end and to the sea at the other. Then as fuel is used the bags inflate with seawater to eliminate the increase of buoyancy that would otherwise take place. The other alternative requires an even greater increase in hull length.

Extra tanks are provided that are empty when the fuel tank is full but fill with seawater as fuel is used.

When the prime mover is an internal combustion engine a major cost is that of the fuel oil.

This can be minimised in one embodiment of the invention by cultivating a small amount of floating seaweed for conversion to natural gas that is substituted for fuel oil. For this purpose an anaerobic digester is provided that is just sufficient for operation of the engine. This digester is formed as an extra section of streamline shape and added in front of the main hull.

Digestion requires operation at about 35 degrees Celsius and so the waste heat from the engine is utilised for maintaining the required temperature. For example the cooling jackets of the engine are provided with pipes that pass through the digester and the exhaust pipe from the engine can be passed through it as well if this is required.

The invention can also be used as a tug boat for purposes other than ocean cultivation.

Outside of the growing season this roll could be a useful application. In this case a towing cable is best attached to an eyelet provided at the rear end of the pod housing the propeller so as to minimise the difference between the line of thrust and the line of drag.

When the invention is applied for the cultivation of a floating seaweed crop that is used to produce natural gas by anaerobic digestion it is desirable to recycle to the sea the nutrients that are recovered as a solution in the water delivered from the digestive process. The quantity will be about 90 percent of the weight of wet weed harvested. The invention then provides recycle bags to contain this fertiliser so that it can be uniformly distributed.

In one embodiment a second winding drum and cable is provided preferably located in the conning tower in order to tow a recycle bag. Instead of being rigid any recycle bag is made of canvas or rubber or strong flexible plastic so it collapses as it is emptied. The recycle bag needs to have about twice the internal volume needed to provide the buoyancy required for countering the downward force of the uppingvane. With such a volume refilling from a tanker needs to take place about every hour. The drag of such a recycle bag is very small compared with that of the uppingvane and so both the diameter of this cable and the winding drum to which it is attached can be much smaller than those concerning the uppingvane.

hi order to counter wave effects one embodiment of the invention has a gear pump/motor and a high and a low pressure accumulator of the kind already described with reference to the uppingvane. A simpler means is a heavy weight attached to about the centre point of the cable. The cable needs a curved guide situated above it to prevent an excessive radius of curvature the curved guide being fitted with a clamp that grips the cable and with a streamlined weight hanging below. Vertical motion of the weight allows constant variation of separating distance between hull and recycling container to be accommodated. A further alternative has a coiled spring attached in series with the cable. In the latter two cases no winding drum need be provided.

A spray nozzle is attached one at each side of the hull and a pump is provided for deployment of these recycled nutrients. Operation involves each cultivating unit comprising tug uppingvane and recycle bag making repeated traverses over a selected area of sea or travelling in a spiral path so that re-fertilisation of the entire area occurs about once every two weeks. In this way an adequately uniform distribution of nutrients is achieved that are greatly depleted by the time the next supply of nutrients is delivered.

A commercial marine farm having floating seaweed as a main crop will comprise a multiplicity of cultivating units of the kind already described together with several carriers.

The latter will transport recycling nutrients for delivery to each cultivating ship in turn and then return to port after filling its hold with weed for delivery to the digester. As will be shown later each cultivating unit of the minimum viable size will cultivate about 46 square kilometres of sea so that each will have an average separating distance of about 7.6 kilometres. This distance is scaled up in direct proportion to any scale up of the cultivating ship. If a gas or diesel engine is the prime mover maintenance is carried out about every twenty days and so a servicing crew together with servicing boat is also required to complete a commercially viable open sea marine farm whose main product is natural gas with fish and net carbon sequestration as by products.

In order to provide the technical background needed for evaluation and since the theoretical basis has not been published elsewhere the theoretical basis of the uppingvane will now be presented.

Showing energy amplification by an uppingvane is potentially very high.

An uppingvane is a hydrofoil and like a wing produces a vortex pair confined in a volume of fluid that moves bodily in a plume quite separate from the sulTounding fluid. The plume has a cross section known as a Rankine Oval. Very little friction drag and mixing with surrounding fluid are involved since the vortices act like a pair of roller bearings with motion at the edges differing little from the relative motion of the surrounding fluid. Spreading due to mixing is veiy small and a size increase of 1% of distance travelled at all edges of the oval is a reasonable assumption based on observation. There will be an induced drag due to providing the upward impulse to the plume and a profile drag due to fluid friction of the uppingvane. Since the following equation has not appeared yet in the literature a derivation is provided in the following.

The cross-sectional area, of this Rankine Oval', is ARC. with h as the span of the uppingvane and with S as its plan area. The horizontal axis of the oval is near enough 1.25 times the vertical axis though this is not important for the present study. Then: ARO = 0.75b (From experimental data based on aspect ratio = 6) III And the mass in0 of seawater thrown up per second when the hydrofoil is propelled at horizontal speed ii then becomes: in0 =pA)u =0.75bpu [2] Now the oval is deflected from the horizontal by angle 8 but still has the same relative speed u to the hydrofoil. friction ignored. Therefore, relative to surroundings when the at vertical component of velocity is v0 the oval will have a forward speed VD that produces induced drag such that: v0/u=sinO & vD/u= l-cos8: so vDIu=l_1_sin2 9 llence: v1,/u = l-1-(v0/i4 [3] From conservation of momentum the induced drag D = mOXYD and so from 121 & 131 the drag becomes: = 0.75b2p?( I -1-(v0/u)2) [4] A profile drag' due to fluid friction has to be added hut this cannot he assessed until the plan area S of the hydrofoil is known. Ihen with a lift coefficient C,. the lift L becomes by convention: L=C145pu [5] Ihis lift, pointing vertically downward in this case, is produced by the rate of change of momentum in the vertical direction of the Rankine oval and from [2] this is: L = rn0v0 = 0.751? Pu: v0/u [6] Equating [5] and [6] yidds the required plan area as: [7] CL/2 u Then since the profile drag D,. by convention with drag coefficient CDT is: D =CDTSPU So combining with [7] becomes: 0.751? v0 DL = pu [8] CL/CDT U ihen the total drag D being the sum D = D, + D using [4] & IS] becomes: i 2 D=0.75b2pu2 i-.*Ji---+ [9] j CL U What is needed, however, is the ratio of ideal power consumed. Dii. to the mass of oval liFted.

hence from 121 & 191: =2 1 + Cob VU HI0 ii) CL ii But only vo is known and vIu can be specified and so the above needs to he given as a non-dimensional form of power coefficient W7, as: WfU= Dii [l_VI_(vo/uY C011L11 [10] (v0 / u) V0 / ii is horizontal speed of uppingvanc mis W= Dii where Wis towing power in watts and D the drag in Newtons with: Wm is a non-dimensional Lowing power coefficient.

v0 is the vertically upward velocity imparted to the plume rn/s CL is the lilt coefficient (infinite aspect ratio and 0.8 to 1.2 are suitable) CDI is the profile drag coefficient (infinite aspect ratio and 0.01 to 0.02 with above) in0 is the mass flow in the plume in kg/s and in0 = p ARO ii where the cross sectional area of the Rankine oval ARO = 0.751? where: h = span of the uppingvane in metres. The value 0.75 matches experimental data on MACA aerofoils with CL = 1.2. This means that the Rankine oval is equivalent to a circular cross section of diameter dR = 0.977 b From [10] drag can be alternatively expressed as: D = lVfi,XPXIROXVO2 [11] Drag hardly changes over a wide range of hull speed ii. Indeed for C,=l.2 and CDF = 0.02 the value of non dimensional power W?, changes surprisingly little as shown below: vju 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.6679 0.5884 0.5673 0.5634 0.5692 0.5833 0.6072 And then with FH,, as the energy equivalent of the hiomass produced based on the lower calorific value LCV of dry seaweed it is readily shown that since the rate of P supply with PQ as P concentration in seawater will he ARU ii I and with PEJO being the proportion of P by weight of dry hiomass and using [11] the energy amplification ratio Eh,/Wis readily shown to be: E. LCV(P /P1110) "U' = LCV = 15,800 JIg for fully dried akac [12] W w pv; With phosphorous concentration in the sea PQ =0.04 gIm3 (at 60 m depth) Concentration in dry hiomass P810 = 0.OO87gPIg hiomass And density of seawater at depth 1028 kg/rn only v0 remains to he decided.

A value of v = 0.2 mIs at the surface is suitable and is assumed throughout my evaluation but owing to increase of the equivalent diameter dR of the Rankine oval as it rises from depth due to accretion of surrounding fluid and to overcome negative buoyancy the vertical speed t0 at the origin point at depth will he greater than v. The increase of size due to mixing has to conserve momentum. A simple and accuratc method of evaluation takes the arithmetic mean lo of two approximations to be called rise and mix' and mix and rise'. The following provides a worked example assuming a static head h0 = (101 m as representing the negative buoyancy to he overcome based on available data (the dashed line given in FIG. E4 for a depth of 60 m where the PQ = .0403 g/m3 in Patent Application Number: GB 1208480.2 dated 15/05/2012) We take as example a span b = 12 m so that with suffix o for origin' the equivalent diameter of the Rankine oval is CIRO = 0.977x 12 = 11.72 m. The plume of this diameter at origin depth grows by 0.02x50 m = 1.0 m to become: di? = 12.72 m so d/ d0 = 1.085 I or example if the plume rises first without mixing the speed due to negative buoyancy will fall from Vo to say Vr given by v12 = Vo -2gh. Then the plume increases in mass in ratio: (dR / 1iw)2 due to mixing and so the speed at the surface reduces to v = Vr (dRo / dR)2 So after substituting for v1 and reaTanging we obtain: rise and mix' giving: vOA = V(dRIdRO) v2 + 2gh0 = 0.5016 rn/s [13] mix and rise' gives: VaR = (dR/dRo)2]v2 + 2g h0 = 0.5721 mIs [14] The average is: = 0.5368 m/s If now we choose vc/à = 0.5 then the towing speed becomes 1.074 mIs or 3.86 kmih If however we choose a design speed of 2 ni/s or 7.2 km/h then iteration yields: = 0.2752: vo = 0.5506 and from [10] Whecomes 0.5704 l'he elTective diameter of the Rankine oval becomes 11.72 m giving /tRO = 107.9 m2 Then equation[11] gives the drag D as 19,193 N and at u=2 mis towing power = 38.4 kW.

The energy amplification ratio obtained from [12] and for vcAi = 0.5506 becomes: Eh,JW= 411.8 Multiplied by the towing power yields an energy output in hiomass as 15.82 MW Some Figures provided from a detailed computer analysis now Follow For this case.

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Q m3/s niBlo En,o Left Drag -F S IJp'n C m Prop dry g/s MW kW kN Ilull N m ITp'n D, m 216.1 1001 15.82 42.2 375 122.3 21090 40.5 4.13 3.01 Column (1) is the volume flow from the uppingvanc and (2) the resulting total hiomass production ii fully dried. The harvested weight would be 10 times as high. Column (4) is the ideal power needed inclusive of streamline towing cable and three times hull drag to allow for towing a recycle hag. This total drag is only 1.099 times the uppingvane drag. The plan area S of the uppingvane is given in column (8) and its average chord given in colunm (9).

The propeller tip diameter is given in column (10) based on a jet propulsion efficiency of 75% and a blading efficiency of 80% resulting in an overall propulsion efficiency of 60%.

Then a mechanical efficiency for the reduction gears is taken as 96% so that the engine power requirement becomes 73.3 kW. Ihen with a thermal efficiency assumed as 35% the energy input to the engine as fuel becomes 209.4 kW.

With full recycle of nutrients and half the hiomass production represented by phytoplankton the figure in column (3) represents the energy equivalent of the seaweed harvest with the same value producing phytoplankton from which about 2% will convert to fish with the result of carbon sequestration. however the conversion efficiecy of seaweed to natural gas from chemical analysis is 76% so dropping the output as natural gas on an LCV basis to 12.0 MW So the net output as natural gas becomes 57 times the energy needed for cultivation.

More energy would he consumed by transport and weed harvesting. But even if the resulting ii gain ratio then reduced to as low a value as 20 the return on energy investment would be considerable since only 5% of the energy yield needs to he used by the marine farm.

The area of sea cultivated would be about 46 square kilometres with a separating distance of only 19 mctrcs between traverses for this casc with seaweed harvested and with re fertilisation every 14 dayc.T'he coresponding separating distance between the cultivating units described in this invention is then 7.6 kilometres.

These figures suggest the invention should he very commercially viable.

When anaerobic digestion is provided a residence time for the wet seaweed of about 25 days is needed. 1'hen for application to the example given in the previous table a wet seaweed input of 10 times the dry value is needed and becomes 10.01kg/s or 21,620 tonnes in 25 days.

This figure is also about the volume in cubic metres of the digester needed to convert the entire crop into natuural gas. However, the engine requires only 1/75 th of this and so the volume required is reduced to 286 m3.

Economic evaluation based on CO2 sequestration trading credits 1 Euro = £08374 so9 Euros/tonne of CO2 =U.537/le At this stage only the target capital costs that would allow profitable operation are estimated.

A 12 m span uppingvane towed at 2 mIs will produce an average fully dried hiomass yield of 1001 g/s at 100% utilisation falling to 900 g/s at an achievable utilisation of 90% There are 0.358 kg carbon/kg dry hiomass so carbon sequestered = 0.322.2 kg/s But CO2 is 44/12 times weight of carbon so CO2 sequestered = 1.181 kg/s Over the 7 month season this becomes: i.181x3600x24x365x7/12/i000 = 21,726 te @ £7.537/te the annual credit due is: £163,746.

This figure is applicable to the case where no seaweed is produced or the ease when the biomass produced as seaweed equals that of the phytoplankton but with all nutrients from anaerobic digestion recycled to the sea To determine the ratio of capital to annual costs the published experience of Vestos V 80 offshore turbine of 2 MW rated power will he utilised. This is reasonable since similar maintenance and interest costs can he expected.

In 2004-2005 the cost of this 2 MW olTshore wind turbine was £2.4 million and @ 10% interest requires £6.11 million paid over 20 years meaning £306,000/year. To this is added £75,000 maintenance.

So the total annual cost is £38 1.000 for offshore 2 MW turbines. There are no wages for offshore turbines or the upwelling units.

The ratio of capital to annual total cost is therefore £2,400,000/38 1,000 = 6.3 I'hercfoit assuming this ratio to apply and if a 30% profit margin is allowed then ignoring fuel cost (only allowable if natural gas produced on site is used as fuel) money reinvested for capital and maintenance from carbon credits becomes £163,746x0.7 = £114,622.

Ihen based on the above ratio of 6.3 the acceptable capital cost of the tug plus uppingvane becomes: £1 14,622x6.3 = £722,120.

And this is for carbon credits alone without any fishing levy that ought to be due since the scheme will more than double the fish stocks that do the carbon sequestration (and marine biologists say many species are threatened by over fishing).

however, if no natural gas is made available as in the case where no seaweed is grown a fcssil fuel such as diesel oil has to be used. i2

An engine is required providing 74kW at about 60% of full load in order to obtain long life and most economical operation so the rated power will be 123kW (165 hp) Assuming a theniial efficiency of 35 % and continuous operation for a 7 month growing season at utilisation of 90% requires 122,900 litres of diesel oil. The fuel price will be assumed equal to that of domestic heating oil at £0.6/litre.

Then the annual fuel cost becomes: £73,740 Ihis is a large fraction of the £114,622 allowable from carbon credits leaving: £40,882 Ibis makes the allowable capital cost per tug and uppingvane £40,882x6.3 = £257,560 Whilst these figures have to be regarded as provisional the analysis does indicate that the major cost will he fuel oil for this application of the invention.

If half is harvested as floating weed with full nutrient recycle after anaerobic digestion to provide natural gas as another product then output as biomass in seaweed is equal to the value already given since the cultivated area is doubled to Asea = 46 km2 per uppingvane. The average natural gas output per unit at 90% utilisation starts from the energy equivalent value of 15.82 MW given in the previous table. Then at 90% utilisation this reduces to 14.24 MW.

With conversion efficiency to natural gas ol 76% the gross output is 10.82 MW. Then with 5% returned for driving the farm machinery the available average power = 10.28 MW.

This converts for the growing season to 52.5 (JWh If cost is 0.1 retail value of 4.0 p/kWh then £0004/kWh = £4000/GWh can be allocated to cover operational cost.

l'his results in providing the annual allowance per unit of 52.5x14,000 = £210,000 Then using the same factor of 6.3 the permissible capital cost becomes £1,323,000 Adding carbon credits gives a total allowabk capital cost of £1,486,700 For each tug and uppingvane unit driven by part of the natural gas produced.

The cost of operation of carriers and weed harvesters has not yet been evaluated hut would probably still not more than treble total costs of operation. This would raise the cost from 10% of gas retail value to 30% of retail value.

A careful design study based on the use of mild steel has shown the total empty weight of the tug and 12 metre span uppingvane would he: hp diesel engine operating at 65% oF rated power (73 kW) 807 kg Shafts and spur gear 170 kg Two Nade propeller with main spar of 0.9%C steel stressed at 20.000 psi 1680 kg Skeg: 450 kg: pod 320 kg: Skeg + Pod: 770 kg Cable in 0.9% C steel stress 30,000 psi 80 m long 385 kg Cable drum and accessories 400 kg Main hull 6mm (1/4") plate 2190 kg: conning tower 1060 kg: Hull: 3520 kg Rudder 100 kg l'otal displacement 7830 kg Uppingvane span 12 m: plan as half disc: lift force 84140 N: main spar 10 te skin plus frames and towing strut 10 m long 5 te l'otal empty weight of tug and uppingvane is: 23 tonnes.

(If reinforced concrete is the constructional material of the uppingvane then its weight will be 17 tonnes to achieve neutral buoyancy) So allowable capital cost per tonne for viability on carbon credits alone with operation on fuel oil and with no seaweed crop is: £257,560/23 tc Yielding an acceptable specific capital cost per tonne of: £11,200/tonne. i3

This figure should not he too difficult to attain.

And with natural gas as major product becomes £ 1,486,700/23 = £64,640/tonne.

Unit costs per tonne should be far less than this making marine farming for natural gas from seaweed appear to be a very commercially attractive proposition.

Cultivation of a square of the North Sea of side 500 km with 23 km2 cultivated per 12 metre span uppingvane would require 11,000 tug/uppingvane units without a seaweed crop and about half that number with a seaweed crop and full nutrient recycle. i4

Specific embodiments of the invention will now be described by example only with reference to the accompanying drawings in which: Figure I shows a side sectional elevation ola tug boat towing an uppingvane on a cable Figure 2 shows a cross section of the apparatus illustrated in Figure 1 Figure 3 shows a plan view of an uppingvane of delta shape plan form.

Figure 4 shows a plan view of an uppingvane of half dl ipse plan form.

Figure 5 shows a plan view of an uppingvane of rectangular shape.

Referring to Fig.1 showing a side sectionai elevation of the invention to the sca'e shown above Fig.l the main hull 1 is shown that is designed to operate submerged with its centreline at a depth of two metres. To withstand the pressure using a cheap constructional method the cross section is made octagonal as shown in Fig.2. Using mild steel plate of 6mm thickness no frames are provided. To provide minimum buoyancy for mitigating the effect of strong waves a conning tower 2 of streamline plan Form and only one metre beam attaches to the main hull and emerges] .5 metres above sea level marked S..L. The combination constitutes the hull and is fully enclosed with hatches provided to allow access by a maintenance crew.

[his embodiment of the invention is arranged to operate as a remote controlled robot though room is available for a small crew if one was required for some purpose. A diesel engine of rated horse power is shown at 3 having an air inlet pipe 4 and exhaust pipe S emerging well above sea level. A fuel tank 6 is provided of 0.5 cubic metres volume that has to he refilled daily. If operation is required for 21 days to coincide with engine servicing then tanks tota'ling 10 m3 would be required. lhis would require the main hull to he increased about 3.4 metres in length and to eliminate buoyancy increase as fuel is consumed bags inside the tanks need to be progressively filled with seawater.

The output shaft of the engine connects through a clutch that is not shown to drive a pinion. This is a bevel pinion meshing with crown wheel as shown at 7 with the crown wheel fixed to the vertical shaft 8. The combination forms a 7:1 reduction gear. Attached to verical shaft 8 at its bottom end is another pinion meshing with a very large crown wheel 9 to provide a further reduction gear of ratio 5.1 so that an overall reduction from the engine of 35:1 is provided to drive a horizontal propeller shaft. This enables the propeller 10 that is fixed to the same propeller shaft to operate at its design speed of only 57 revolutions per minute with the engine operating at 2,000 revolutions per minute.

The propeller has two blades lithe tips oF which are attached to shrouds 12. these shrouds have the same chord as the blade tips and are bent to a circular arc centred on the axis of rotation. The shrouds extend in the direction of the axis of rotation for an appropriate distance both in the forward and rearward direction. [he purpose of these shrouds is to minimise the how over the blade tips that reduces thrust and leads to wasteful strong tip vorticies. The blades are shown with considerable chord near the root section in order to produce uniform torque over the entire blade ength. Without some way of countering the propeller torque the hull would tend to he rolled about its longitudinal axis, To prevent this a skeg 13 is provided of streamline cross section and has a camber at least near the propeller blade root position in order to act as a stator to remove some of the vortex motion and produce a pressure rise by converting the kinetic energy associated with that vortex motion to a pressure gain. The skeg also provides the structural member needed to support the is streamline shaped pod 14 that contains the propeller shaft and gears 9. To provide further cancellation oF the vortex caused by the propeller a skeg extension 15 is provided attached to the pod 14 at its underside and reaching a depth slightly greater than to which the blade tips reach. Further guidancc of flow can optionally by provided by short horizontally oriented vanes 16 that are not shown except in Fig. 2.

An uppingvane 17 is shown in section at its centreline and consists of a hydrofoil operated with its leading edge at a lower level than the trailing edge in order to deflect a plume of seawater toward the surface of the sea. An uppingvane cable drum 18 is provided located in the main hull 1. It could be alternatively located in the conning tower 2. The uppingvane cable drum has cable 19 wrapped around it and extending through a tube in skeg 13 and skeg extension 15 the tube having curved cable guide 20 attached to prevent excessive bending of the cable. The cable 19 ends in an eyelet attaching through a clamp 21 to a delta bar 22. This consists of a bar of streamlined cross section bent near the middle and attached to the upper surface of the uppingvane to form a triangle.

The cable drum 18 is mounted on a shaft having a horizontal axis and on which a spur gear 23 is also fixed. This spur gear cooperates with a pinion connecting to a gear pump/motor 24. Two accumulators 25 and 26 are provided one of which operates near atmospheric pressure with the other having a very high pressure and one port of the gear pump/motor connects to the bottom of one accumulator and the other port to the bottom of the other accumulator so that the force on the cable is balanced by the pressure on the teeth of the spur gear 23. Another gear pump 27 is driven From the engine via any kind of transmission inclusive of a clutch or switch in order to fill the high pressure accumulator from a store or the low pressure accumulator in order to provide the correct pressure and a stop valve 28 is provided as an optional extra.

A rudder 29 is provided for steering and is preferably operated by hydraulic remote controlled actuators that obey signals from an on hoard computer that in turn is provided by latitudes and longitudes from orbiting satellites. In this way the tug is made able to fertilize a specified area of the sea with the required degree of uniformity and operated robotically so that no crew is required. A mast needed for navigation lights and radio antenna is not shown.

When the marine farm includes the recycle of nutrients recovered from conversion of seaweeds to fuels then recycle bags are required. In Fig. 1 a towing cable 30 is provided for a liexible hag type of container. Any kind of towing method having the flexibility needed to accommodate the strongest waves that can he expected can be provided. In Fig. I a scaled down replica of that used for the uppingvane is illustrated with the cable deployed from towing cable drum 31.

Referring now to Fig. 2 a cross section of the invention is shown taken through the engine 3 looking from the direction oF how to stern. The octagonal shape of the main hull I is shown together with the narrow cross section of conning tower 2 with combination oF I and 2 constituting the hull. This profile illustrates the principle of minimum buoyancy on which the hull is hased with small plan area penetrating the surface of the sea. This arrangement minimises the response to large sea waves. What is also clearly illustrated is the very large area of the actuating disc that propeller 11 traces out as it revolves. The area of the actuating disc is that enclosed by the chain dashed circle and pod 14 the diameter of the pod being the same as that of the huh of the propeller. What is novel here is the area of the actuating disc exceeding that needed to provide the buoyancy needed to counter the force on the cable 19 and the weight of the hull and its contents. Propeller I I has a shroud 12 fixed to each blade tip to minimise flow over those tips and so improve the total propeller thrust. The pod 14 is supported by and fixed to skeg 13 which is in turn fixed to the bottom of main hull 1. There is a skeg extension 15 fixed to the bottom of pod 14. 1 xtra horizontal stator vanes 16 are also provided but do not extend to a distance as great as the radius of the propeller tips. Together with skeg and slceg extension a stator is provided able to substantially remove vortex flow caused by the propeller I I thereby cancelling most of the torque reaction produced as a result of driving the propeller. A curved cable guide 21) is fixed to the bottom of the skeg extension 15. Cable 19 is passed through both skeg and skeg extension being wrapped round winding drum 18 at its upper end and attached to the delta bar 22 that is fixed to uppingvane 17. A towing cable drum 31 is also shown hut is not required unless the recycling of nutrients from processed floating seaweeds is incorporated.

Referring to figs 3. 4 and 5 a range of plan views of possible uppingvane embodiments arc shown. AU have the same span of 12 metres and the same plan area as required for towing at a speed of 2 metres per second in order to send a plume of seawater from a depth of 60 metres to the surface of the sea to start spreading in both transverse directions at 0.2 metres per second. Fig.3 shows a triangular shape also known as a delta plan form. Fig.4 shows a bisected elliptical plan form that is close to a bisected disc and is the presently preferred embodiment of the invention. lig.5 shows a rectangular plan form. Flows over the outer tips would add extra drag and to minimise the strength of vortex cores two sets of hydrofoils 32 of short span and chord are provided. These turn the Ilows going over the tips toward a direction opposite motion to minimise drag by utilising the kinetic energy that would otherwise be wasted to create excessively rapidly rotating vortex cores. This feature is however covered in detail in a previous patent specification number: (iB09052 13.5 dated 26/3/2009.

This feature could also be applied to the plan forms illustrated in Figs. 3 and 4.

In each ease a bending moment caused by the force on the uppingvane cable needs to he resisted and a main spar of preferably high carbon steel can be provided. Ihe uppingvane need not be constructed entirely of metal and can even he made with very little metal. It can be constructed of reinforced concrete with most of the reinforcement close to the upper surface which is in tension. It preferably contains adequate voids in order to ensure it has small positive buoyancy. Alternatively an uppingvane can have a strong plastic skin the interior filled with structural foam. Some concrete ballast can optionally be included to counter any excessive buoyancy.

Claims (1)

1. <claim-text>CLAIMS1 A tug boat containing at least one pnme mover being an internal combustion engine or any kind of motor connected by a power transmission system to at least one propeller and in which the hull of the tug boat is attached by a linkage means such as a cable to a hydrofoil at a point close to its centre of pressure so that the leading edge of the hydrofoil to he called an uppingvane operates at a lower level than its trailing edge and is arranged to be deployed at such depth that a plume of seawater containing a higher concentration of the nutrients needed for the growth of marine organisms than exist at the surface of the sea are delivered to the photic zone of the sea.</claim-text> <claim-text>2 A tug boat as claimed in Claim 1 in which a so called uppingvane winding drum is provided about which an uppingvane cable is wound and is attached at its lower end to the uppingvane the winding drnm being fixed to a horizontal axle on which a spur gear is also fixed the axle being located by bearings fixed inside the hull of the tug boat and in which the spur gear cooperates with a pinion connecting with a driving means..</claim-text> <claim-text>3 A tug boat as claimed in Claim 1 in which the area traced out between the blade tip and blade root of a propeller blade in one revolution added to the same area traced out by any other propellers ii more than one is fitted is greater than the underwater projected frontal area of the hull of the tugboat which incorporate those propeller blades.</claim-text> <claim-text>4 A tug boat as claimed in Claim 1 in which the motor is an electric motor that can be though not necessarily is connected to a fuel cell.</claim-text> <claim-text>A tug boat as claimed in Claim Ito 3 in which the output shaft of the prime mover is horizontal and a bevel pinion connects through a clutch with that output shaft and this bevel pinion cooperates with a crown wheel fixed to an intermediate vertical shaft to whose lower end a second bevel pinion is fixed and this cooperates with a large crown wheel that is fixed to a horizontal propeller shaft and to which a propeller is fixed at the opposite end of that propeller shaft so that a double reduction gear is provided with the axis of the propeller located at a greater depth than the engine.</claim-text> <claim-text>6 A tug boat as claimed in Claim 5 in which a propeller is located by bearings inside a pod that is connected to the bottom of the hull by a so called skeg that is hollow and has the intermediate vertical shaft passing through it.</claim-text> <claim-text>7 A tug boat as claimed in Claim 6 in which a skeg extension is provided attaching to the underside of the pod and having its lower end at least as deep as the depth reached by the propeller blade tips both skeg and skeg extension being of hydrofoil cross section and so arranged as to remove the rotating component of the flow leaving the propeller in order to substantially eliminate torque reaction.</claim-text> <claim-text>S A tug boat as claimed in Claim 7 in which a pair of short horizontally oriented vanes is fixed to the pod one on each side in order to assist in removing rotation of the flow a least at small distances measured from the axis of rotation.</claim-text> <claim-text>9 A tug boat as claimed in Claim 1 or 2 in which the output shaf't of the prime mover is connected to an alternator that provides an electric transmission to a rim driven propeller in is which the tips of the propeller have a cylindrical ring attached to them containing a multiplicity of penilanent magnets that cooperate with a multiplicity of coils connecting with the alternator so that the effect of a reduction gear is provided.</claim-text> <claim-text>A tug boat as claimed in Claim 7 in which the uppingvane cable passes through a tube fixed inside the hollow slceg the pod and thc skeg extension.</claim-text> <claim-text>11 A tug boat as claimed in Claim 1 or 2 in which the tug boat has a main hull that can operate submerged when towing an uppingvane and has a so called conning tower attached to its upper surface that is of streamline shape hut relatively small plan area in order to minimise vertical motion under strong wave conditions the combination of main hull and conning tower comprising the hull.</claim-text> <claim-text>12 A tug boat as claimed in Claim 1 or 2 in which the uppingvane is attached to the uppingvane cable through the intermediary of a delta bar that consists of a bar of streamline cross section made in the form of two sides of a triangle with the position joining these sides uppermost and forming the position at which the uppingvane cable is attached the leg of the delta bar nearest the leading edge of the uppingvane being joined to the upper surface of the uppingvanc by a hinge whilst the other leg is made of a more flexible material or is attached by a spring of some kind preferably close to the lower surface of the uppingvane whereby the angle of incidence is changed when the force on the uppingvane cable changes.</claim-text> <claim-text>13 A tug boat as claimed in Claim 2 or 12 in which the uppingvane cable drum is fixed to a horizontal shaft mounted in bearings attached to the hull and in which a spur gear is fixed to the same shaft and which that spur gear meshes with a pinion coupling with a gear pump/motor the inlet and outlet ports of which connect through pipes to accumulators maintained at different pressures so that force on the uppingvane cable is balanced hut allows the drum to wind and unwind as the hull of the tug nses and falls due to ocean waves.</claim-text> <claim-text>14 A tug boat as claimed in Claim 1 or i3 in which the said uppingvane is constructed of reinforced concrete with reinforcement mainly close to the upper surface and in which voids are provided within the hydrofoil shape in order to achieve positive buoyancy.</claim-text> <claim-text>A tug boat as claimed in Claim I or 13 in which the said uppingvane has an outer shell made of a strong plastic material and the interior filled with structural foam or wood together optionally with some concrete as ballast.</claim-text> <claim-text>16 A tug boat as claimed in Claim 1 or 13 in which a towing cable is provided attached to a recycle hag that can he filled with nutrient rich water for spraying on the surface of the sea.</claim-text> <claim-text>17 A tug boat as claimed in Claim 11 in which the main hull is internally pressurised to prevent the entry of seawater through a duct provided for deployment of the uppingvane cable.</claim-text> <claim-text>18 A tug boat as claimed in Claim 17 in which a turhocharged engine is incorporated and in which both the outlet port of the turbocharger compressor and the air inlet port of the engine are open to the interior of the main hull to provide it with internal pressurisation and with fans arranged so that the air is f'irst cooled by contact with the internal walls of the main hull before entering the inlet port of the engine. II)Amendments to the Claims have been filed as followsCLAIMS1 An ocean cultivator system comprising a tug boat containing at least one prime mover that is connected by a power transmission system to at least one propeller, the hull of the tug boat being attachcd by a linkage means to a hydrofoil such that in use, when thc hydrofoil is deployed at an operating depth. thc leading edge of the hydrofoil is positioned at a lower lcvcl than its trailing edge to direct a plume of nutrient rich seawater towards the photic zone of the sea, wherein the plan area of the hydrofoil is substantially greater than the underwater projected frontal area of the hull of the tug boat.2 An ocean cultivator system as claimed in claim 1 wherein the linkage means comprises a cable which is attached to the hydrofoil by means of a streamlined delta bar that has one leg positioned nearest to the leading edge of the hydrofoil and is attached to an upper surface of the hydrofoil by means of a hinge and one leg that is either made of a flexible material or is attached by means of a spring to the hydrofoil to counter the undesirable effect of large waves on the cultivator system.3 An ocean cultivator system as claimed in claim 2 wherein the linkage means further comprises a winding drum about which the cable is wound, the winding drum being mounted on a horizontal axle mounted within the hull of the tug boat and being driven by a hydraulic motor to wind the cable in and out during deployment or retrieval of the hydrofoil, wherein the hydrauhc motor is further provided with an accumulator that compensates for vertical motion of the tug hoat due to wave action such that this motion is not applied to the cable or r the hydrofoil.0') 4 An ocean cultivator system as claimed in any preceding claim wherein the power 0 transmission system comprises a horizontal output shaft that extends from the at least one prime mover to a first bevel pinion that connects to the output shaft with a clutch, the first r hevd pinion cooperating with a first crown wheel fixed to an upper end of an intermediate vertical shaft, a lower end of which is connected to a second bevel pinion that cooperates with a second crown wheel that is fixed to a horizontal propeller shaft, to which the at least one propeller is fixed, such that a double reduction gear is provided and the axis of the propeller shaft is positioned below the axis of the output shaft.An ocean cultivator system as claimed in claim 4 wherein the at least one propeller is mounted on a watertight pod that houses the bearings of the propeller, the watertight pod being itself mounted within a hollow skeg that extends from the bottom of the hull of the tug boat, wherein the intermediate vertical shaft extends within the skeg.6 An ocean cultivator system as claimed in claim 5 wherein a skeg extension extends from the underside of the watertight pod to a depth at least as deep as the depth to which the blades of the at least one propeller extend, wherein both the skeg and skeg extension are of streamlined cross section and are so arranged to remove the rotating component of the flow leaving the at least one propeller to substantially eliminate torque reaction.7 An ocean cultivator system as claimed in claim 6 wherein a pair of horizontally extending vanes are fixed either side of the watertight pod to assist in removing rotation from the flow.S An ocean cultivator system as claimed in claim 6 wherein the cable extends through a tube fixed inside the skeg. watertight pod and the skeg extension..9 An ocean cultivator system as claimed in claims I to 3 wherein the power transmission system comprises a horizontal output shaft that is connected to an alternator that provides an electric transmission to the at least one propeller that is rim driven, wherein the tips of the propeller blades have a cylindrical ring attached to them containing a plurality of permanent magnets that cooperate with a plurality of coils connected to the alternator so that the effect of a reduction gear is provided.An ocean cultivator system as claimed in any preceding claim wherein the tug hoat has a main hull that can operate submerged and has a conning tower attached to its upper surface that is of streamlined shape but relatively small plan area in order to minimise vertical motion under strong wave conditions.11 An ocean cultivator system as claimed in claim 10 wherein the main hull is internally pressurised to prcvcnt thc cntry of seawater through a duct provided for deployment of thc cable.12 An ocean cultivator system claimed in claim 11 wherein the at least one prime mover comprises a turhocharged engine, with both an outlet port of the turbocharger compressor and an air inlet port ol the engine being open to the interior of the main hull to provide it with internal pressurisation. wherein fans are provided within the main hull such that air is driven C\J within the main hull into cooling contact with the walls of the main hull before entering the inlet port of the engine.0') 13 An ocean cultivator system as claimed in any preceding claim wherein the hydrofoil 0 is constructed of reinforced concrete with reinforcement being mainly provided close to an upper surface of the hydrofoil with voids being provided within the hydrofoil to minimise r negative buoyancy.14 An ocean cultivator system as claimed in claims 1 to 12 wherein the hydrofoil has an outer shell made from a strong plastic material, the interior of which filled with structural lbam or wood.An ocean cultivator system as claimed in claim 14 wherein the hydrofoil is providcd with concrete as ballast.16 An ocean cultivator system as claimed in any preceding claim wherein a towing cable is provided attached to a recycle hag that can he filled with nutrient rich water for spraying on the surface of the sea.17 An ocean cultivator system as claimed in any preceding claim wherein the sum of all the areas traced out by one propeller blade in one revolution for each of the propellers provided is greater than the underwater projected frontal area of the hull of the tug boat.</claim-text>