GB2442216A - A floating dock with adjustable buoyancy - Google Patents

Abstract

A floating dock 10 comprises a pair of surface floats 12 together with a submersible platform 14 which is capable of being raised or lowered and means for controlling the buoyancy of the platform during raising and lowering. The platform also has a pair of buoyancy towers 16 each of which is slidingly attached to a respective one of the surface floats. The submersible platform may have two pairs of buoyancy towers, each pair being slidingly attached to a respective one of the surface floats. Also disclosed is a method of lifting a vessel in the water which comprises the steps of providing a pair of surface floats 12, providing a submersible platform 14 capable of being raised and lowered below the surface floats and providing a pair of buoyancy towers 16 as part of the platform. Each tower is slidingly attached to a respective surface float. The method further discloses reducing the buoyancy of the platform so as to lower it relative to the surface floats, with the towers sliding relative to each respective float, manoeuvring a vessel to be lifted to a position above the platform and increasing the buoyancy of the platform so as to raise the platform and the vessel, with the towers sliding relative to each respective surface float.

Description

Floating Dock and Method of Lifting a Vessel The present invention

relates to floating docks and to methods of operating floating docks; for use in lifting vessels out of the water for maintenance, repair or other purposes.

Floating docks had been proposed at least by 1928 (vide GB-296,655) and probably have a significant history prior to that date. A certain amount of interest in floating docks existed in the 1970's (vide GB-1462047, GB-I 549753 and GB-2005603). But various problems exist with the practical implementation of these previous proposals, and none of them appear to have been adopted commercially.

A floating dock and method of operating said dock is disclosed in patent application GB-2144375A, which was published on 6th March 1985, and the inventor of the present invention was also an inventor of the floating dock and operating method disclosed in GB-2144375A.

The previously disclosed floating dock comprises a docking vessel together with a submersible platform. The docking vessel has an open area for the reception of a boat. The submersible platform is beneath the open area and is capable of being raised or lowered so as to raise and then lower a boat located in the open area. The buoyancy of the platform is controlled, using buoyancy thr'k in the platform and a supply of compressed air, to effect the raising or lowering of the platform. The use of p0-called "regulating means" (winches and rams) is disclosed to keep the platform level during raising and lowering.

When compressed air is used to raise or lower a buoyancy tank it is very difficult to regulate the speed at which the tank ascends or descends through the water. In raising; the tank starts to ascend slowly but when a critical buoyancy is reached it suddenly accelerates rapidly and unstably towards the surface. In lowering; the tank starts to descend slowly but when a critical buoyancy is passed it suddenly starts to sink rapidly and unstably. For convenience herein this sudden unstable movement is referred to as the "break-away" phenomenon. Control of the speed of assent or descent is critical in providing safe operation when lifting or lowering a boat The problem will be readily appreciated by considering a fin-keel sailing yacht moored on a submerged platform (essentially in the fbrm of a buoyancy tank) which is subsequently raised in the manner described.

The use of winches and rams as disclosed in GB-2144375A may in theory be effective to regulate the speed at which the platform ascends or descends through the water; in addition to keeping the platform level. However, this has proved to be difficult to achieve in practice.

Thus, an object of the present invention is to provide an improved floating dock method of lifting a vessel compared with the arrangement disclosed in GB-2144375A.

According to a first aspect of the present invention there is provided a floating dock comprising a pair of surface floats together with a submersible platform which is capable of being raised or lowered and means for controlling the buoyancy of the platform during raising and lowering wherein the platform has a pair of buoyancy towers each of which is slidingly tthrhed to a respective one of the surface floats.

According to a second aspect of the present invention there is provided a method of lilting a vessel in the water comprising the steps oi providing a pair of surface floats; providing a submersible platform capable of being raised and lowered below the surface floats; providing a pair of buoyancy towers as part of the platform with each tower being slidingly ttachcd to a respective surface float; reducing the buoyancy of the platform so as to lower it relative to the surface floats with the towers sliding relative to each respective float; manocuvring a vessel to be lifted to a position above the platfbnn; and increasing the buoyancy of the platform so as to raise the platform and the vessel with the towers sliding relative to each respective surface float. / Embodiments of the present invention will now be described by way of further example only and with reference to the accompanying drawings, in which-Figure 1 is a scher'mtic perspective view of a floating dock according to one embodiment of the present invention, with the submersible platform in it's fully lowered position; Figure 2 is an end view of the floating dock as shown in figure 1; Figure 3isa side view of the floating dock as shown in figure 1; Figure 4 is a perspective view showing the submersible platform in a pailially raised posifion Figure 5 is an end view of the floating dock as shown in figure 4; Figure 6 is a side view of the floating dock as shown in figure 4; Figure 7 illustrates one arrangement for the sliding attachment of the towers to the surface floats; Figure 8 is a schematic partial vertical cross-section through a surface float and the platform illustrating an arrangement for positive mating of the top of the platform with the underside of the surface float; The basic arrangement of a first embodiment of a floating dock according to the present invention is illustrated, schematically, in figures 1 to 6. The dock 10 comprises two surface floats 12 and a submersible platform 14. The surface floats 12 are of elongate box fonn. Platform 14 is rectangular in plan view and has a buoyancy tower 16 in each corner thereof Each buoyancy tower 16 is slidingly ttc1ied to a respective end of a surface float 12.

The surface floats 12 are essentially separate air-filled hollow boxes intended, subject to variations described below, permanently to float on the surface of the water. Platfonn 14 may be considered as a plurality of buoyancy tanks secured to the underside of a flat plate or series of cross-members. Buoyancy towers 16 are hollow veilical pillars, of rectangular horizontal cross-section, which are rigidly connected one in each corner of the platform 14.

Platform 14 is capable of being raised or lowered relative to the surface floats 12. As platform 14 is raised or lowered, each tower 16 slides vertically on the respective end of one of the surface floats 12. Thus, figures 1 to 3 sh9w the platform fWly lowered and figures 4 to 6 show the platform pailially raised.

The buoyancy of platform 14 is controlled so as to effect the raising and lowering thereoL This is done by supplying compressed air to the buoyancy t2nkR of the platform, venting water (c.& sea water) from the undasides thereof to raise the platform and allowing the compressed air to escape to flood the tanks and lower the platform. Implementing the platform as a plurality of buoyancy tanks provides for greater control than may otherwise be achieved with the platform being in the form of a single buoyancy tank. The compressed air is supplied to the tnkR of the platform via flexible hoses connected to a compressor housed on, or preferably within, one of the surface floats 12.

In this embodiment each tower 16 is in effect a separate, sealed air-filled tank With platform 14 in it's fully lowered position the tops of the towers are above the surface of the Water, as shown in figures 1 to 3. It has been found that the provision of the buoyancy towers very remarkably mitigates the "break-away" phenomenon described above. As compressed air is supplied to platform 14 the buoyancy of the platform increases and it staits to rise through the water. As this happens the towers slide relative to the surface floats and, of course, also rise through the water. The buoyancy of the towers reduces the more the towers rise above the surface of the water. Thus, the increase in buoyancy of the platfonn is partially off-set by the reduced buoyancy of the towers. Moreover, since the towers are tthched to the surface floats the platform is always fted to water-level buoyancy even if the tops of the towers are slightly below the surface of the water when the platform is in it's fully lowered position. The operation is the same if the towers are not sealed air-filled thnk, in that they also can be arranged to have compressed air supplied to them and vented from them. In the extreme, the air space of the towers can be integral with the air space of the buoyancy tank(s) of the platform. However, the greater the number of separately controllable air spaces the greater the control of the dock particularly with regard to horizontal tilt In any event, as the platform 14 is raised or lowered beneath the surface of the water, the volume of the hollow towers 16 which is above the surface of the water varies accordingly. The buoyancy of the towers also varies accordingly and at all times the buoyancy of the platform and the buoyancy of the towers is attatthed to the buoyancy of the surface floats. This arrangement reinaikably mitigates the "break-away" phenomenon as described above. The effect in practical tests is veay dramatic and renders the stability control qf the floating dock during operation so precise as to give great confidence in being able to meet all insurance, health and safety and other such issues to be faced by a commercial iinplenientation.

The range of relative dimensions for the towers, platform and surface floats in order for the observed benefit to be achieved is not especially limited. The floating dock will in practice be dimensioned to receive and lift specific dimensions and weights of boats and the acceptable relative dimensions for the towers, platform and surface floats will readily follow from this. That is, implementelion of the invention can readily be achieved by persons skilled in the sit without a range of relative dimensions being proscribed herein. In similar m2nner although thus far the surface floats have been described as having an elongate box form, the towers as having rectangular horizontal cross-sections and the platform as being rectangular in plan view; such shapes are not essential to the operation of the invention and the shapes of the components may be varied as considered appropriate.

The sliding attachment of the towers 16 with the surface floats 12 assists the stability of the rthing and lowering of the platform 14, including dampening of any tendency for lateral or longitndinal movement of the whole structure. Further the sliding attachment of the towers 16 with the surface floats 12 can be used to assist in controlling the speed of raising and lowering the platform.

An arrangement fbr implementing the sliding attachment of the towers 16 with the surface floats 12 is illustrated in figure 7. The 1ongituAin11y inward facing vertical surface of each tower 16 is provided with a vertically exttnding channel 22 secured thereto. Two horizontal shafts 24 project from each vertical end face of the floats 12. A spindle 26 is held between the distal ends of the shafts 24 and a wheel 28 isrotatably mounted on the spindle, longitudinally aligned with float 12. Further, a respective transversely extending bogey wheel is rotatably mounted on each shaft 24, between wheel 28 and the vertical end face of the float The spacing of the towers 16 on the platlbim 14, length of the floats 12 and dimensions of the sliding arrangement (22 -30) is such that each of the wheels (28,30) runs on a respective vertical surface of channel 22. Positive sliding engagement between the floats 12 and the towers 16 is thus ensured. Equipping the wheels (28,30) with pnemntic tyres can facilitate assembly of the whole (inflate when in situ) and provide an clement of control over the positive engagement between the floats 12 and towers 16. If necessary, control of the rate of vertical movement of the towers relative to the floats can be assisted by applying a braking force (or forees) to the wheels (28,30) -with the addition of a suitabIe conventional, braking mecl1Anim The rate of vertical movement of the towers 16 relative to the floats 12 is primarily controlled by the supply or venting of compressed air in the buoyancy tanks of the platform 14. Additional control of this relative vertical motion can, if necessary, be achieved with the use of winches and/or rams in the mfinner described in GB-2144375A. It will be appreciated that the control being discussed is not just of the speed of ascent or descent of the platform but also control of the levelling of the platform. Any tendency for the platform to tilt, longitudinally and/or transversely, can be counteracted by: differential supply or venting of compressed air to the plurality of buoyancy tanirs of the platform; and/or differential usc of the several winches and/or rams (if fitted); and/or differential braking of the wheels within respective tower channels (if brakes are fitted). Moreover, the whole system can be constantly monitored and controlled by a computer system (preferably housed in one of the floats 12).

One or more mooring pillars are provided to prevent lateral movement of a boat positioned on the submersible platform. Simple warps fore and aft between the boat and the platform are sufficient to prevent the boat tilting longitudinally. The mooring pillar(s) may be rigidly fixed to the platform or may be movable laterally across the platform to better accommodate different boats of different beam. Lat al movement of the mooring pillar(s) may be effected, for example, by winches or hydraulic rams. Furthermore, the floating dock of this invention is not limited to lifting one boat at a time. Clearly, whereas a large scale dock may lift a single large boat the same dock could equally lift several mAller boats simultaneously -subject to the size of the platform and the overall weight being lifterL With the basic arrangement of an embodiment of the invention thus described, it is appropriate to consider various modifications within the basic concept Firstly, the invention has been defined as requiring a "pair of surface floats". It is to be understood that this requirement is not negated simply by providing some form of mechanical link between the "two" floats. In particular a "U"-shaped structure is herein to be considered as providing the required "pair of surface floats' even if the whole of the "U"-shape is constructed as a single air containing structure.

Secondly, the invention has been defined as requiring a "pair of buoyancy towers" each attached to a respective one of the surface floats -whereas the above described embodiment has four buoyancy towers, a respective pair thereof being attached to a respective one of the surface floats. The described embodiment is preferred, but a single tower per float can work -preferably with the tower being slidingly restrained in a notch located at the mid point of the length of the float Many variations to the detail of the described embodiment arc possible. In relation to the sliding attachment described above, one variation which may be beneficial is to replace the pneumatic tyre wheel 28 with a toothed wheel engaged with a toothed rail secured to the inside of the channel 22. Another variation is to use spindle 26 not to bold a wheel but instead to bold one end of a hydraulic ram. The ram is housed within channel 22 and is secured at the bottom of the tower. Relative movement, vertically between the tower and the end of the surface float is controlled by the ram -although the inkin lift is still provided by the buoyancy tanks of the submersible platform.

The surface floats may play a critical role if the upper surface of platform 14 is to be raised above the surface of the water (which is desirable for a number of reasons). It has been observed that considerable instability arises when a large flat, plate-like float breaks through the surface of the water. Even though the towers 16 greatly improve the stability of raising and lowering the platfbrm 14 under the water, it is considered that a moment of considerable instability could occur if the upper surface of platform 14 were allowed, freely, to break through the surface of the water. However, platform 14 is not free to break through the surface of the water, because just as it approaches the surface it comes in to contact with the undersides of surface floats 12. If the upper surface of platform 14 is to rise above the surface of the water it must lift the surface floats out of the water. Thus, as the upper surface of platfoiml4 contacts the undersides of the floats 12 it is as if the floats and platform become a single unit which already has a significant surface area above the surface of the water. This combined with the fact that the buoyancy of the platform now has also to lift the weight of the floats remarkably mitigates the loss of stability which would be expected ifthe surface floats 12 wore not present.

!fthefloatingdock lOisdesignedtoallowtheuppersurfaceofplatform l4tobe raised above the surface of the water then the upper surface of platform 14 and the undarsides of surface floats 12 are preferably arranged to mate positively. One such arrangement is illustrated schematically in figure 8. A surface rail I8is provided adjacent each of the lateral edges of the upper surface of platform 14. Each rail 18 is received in a correspondingly shaped recess 20 on the underside of the respective surface float 12.

Preferably the floating dock of the present invention is capable of being self propelled through the water. Commercially available pump- jet engines arc ideally suited for this purpose. They can be installed, for example, at or in the base of the towers and provide excellent directionally variable thrust without increasing the draft of the dock.

The floating dock of the present invention can provide a number of highly desirable advantages. Firstly, the dock need have only a very shallow draft with the platform folly raised. Thus, the floating dock is easily manovered in shallow water and can provide a roll-on roll-off service for the launch and recovery of boats. This very significantly increases the number of waterside locations which can be used to launch and recover boats -with conventional docks being limited to relatively deep water-side locations. In addition, the substantial foundations and/or piles often required to support the weight of conventional boat lifting cranes can be avoided. The range of usable land areas is thus greatly extended and, of course, the water-side construction costs can be significantly reduced.

The roll-on roll-off service is facilitated by the provision of a movable pallet positioned on the upper surface of the submersible platform. The keel of the boat rests on the pallet as the boat is raised, with the above described mooring pillar and for and aft warps being provided on the pallet Once lifted the boat can be more securely chocked on the pallet if required. When the dock has been manoeuvred to it's waterside unloading area, the pallet is moved off of the platform. For this purpose the pallet may be provided with wheels or, preferably, some form of caterpillar track; with a winch being used to provide the motive power. This winch can be part of the machinery of the dock -so that all that is required ashore is a point to secure a pulley through which the towing line from the winch can be passed. With the above described lifting of more than one boat simultaneously, obviously the corresponding number of pallets are provided.

A further highly desirable advantage which can be obtained with the present invention is that all of it's operating machinery (the air compressors etc) can be housed within bulkheads which can be sealed in a watertight n1nner. Having switched off all of the nchinery and sealed the bulkheads, valves in the surface floats can be opened so as to flood the floats and have the whole dock sink in the water. This arrangement is particularly suited to hurricane prone regions of the world as follows. As a hurricane approaches the floating dock is used to collect the local boats and to move them ashore where they can be securely tethered down.

The dock is taken out to deeper water and sunk, to lie on the sea bed while the hurricane passes. After the hurricane; compressed air hoses are taken down to the dock and connected to purge the surface floats of seawater. On the surf kce the dock is soon ready to resume it's normal operation and the local boats are thus re-launched. It is expected that such an operation using the present invention will very greatly reduce the length of time that the local fleet of boats is out of operation as a consequence of a hurricane. The benefits for fishing fleets and pleasure charter boats is obvious.

Claims (10)

1. A floating dock coinpnsing a pair of surface floats together with a

submersible platform which is capable of being raised or lowered and means for controlling the buoyancy of the platform during raising and lowering wherein the platform has a pair of buoyancy towers each of which is shdingly attached to a respective one of the surface floats.

2. A floating dock as claimed in claim 1, wherein the submersible platform has two pairs of buoyancy towers each pair being slidingly attached to a respective one of the surface floats.

3. A floating dock as claimed in claim 1, further including braking means operable to effect the rate at which one or more of the towers slides relative to its surface float.

4. A floating dock as claimed in claim 1, wherein the submersible platform comprises one or more buoyancy tnk and the means for confrolling the buoyancy of the platform includes a compressor for supplying compressed air to the said buoyancy tank(s) of the platform.

5. A floating dock as claimed in claim 4, wherein one of the surface floats includes a chamber which can be sealed in a th4d tight mmer and wherein said compressor is housed in said chamber.

6. A floating dock as claimed in claim 5, fUrther comprising means for reducing the buoyancy of the dock including means for reducing the buoyancy of the surface floats whereby the whole dock may be sunk below the surface of the water.

7. A floating dock as claimed in claim 1, fUrther comprising means which provide positive in1ing of the upper surface of the platform with undersides of the surface floats as the platform approaches its fully raised position.

8 A floating dock as claimed in claim I, further comprising propulsion means operable to move the dock through the water in a self propelled manner.

9. A method of lifting a vessel in the water comprising the steps of: providing a pair of surface floats; providing a submersible platform capable of being raised and lowered below the surface floats; providing a pair of buoyancy towers as part of the platform with each tower being slidingly altached to a respective surface float reducing the buoyancy of the platform so as to lower it relative to the surface floats with the towers sliding relative to each respective float; manoeuvring a vessel to be lifted to a position above the platform; and increasing the buoyancy of the platfbrm so as to raise the platform and the vessel with the towers sliding relative to each respective surface float.

10. A method of lifting a vessel in the water as claimed in claim 9, further comprising the step of applying a braking foree between the towers and the floats as the buoyancy of the platform is increased.