WO2008038009A1

WO2008038009A1 - Floating dock and method of lifting a vessel

Info

Publication number: WO2008038009A1
Application number: PCT/GB2007/003686
Authority: WO
Inventors: Donald Scott-Thom
Original assignee: Sealift Caribbean Limited
Priority date: 2006-09-29
Filing date: 2007-09-26
Publication date: 2008-04-03

Abstract

A floating dock (10) comprising 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 (14) during raising and lowering wherein the platform (14) has a pair of buoyancy towers (16) each of which is slidingly attached to a respective one of the surface floats (12). Preferably, the submersible platform (14) has two pairs of buoyancy towers (16) each pair being slidingly attached to a respective one of the surface floats (12). Also, a method of lifting a vessel in the water comprising 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 (12); providing a pair of buoyancy towers (16) as part of the platform (14) with each tower (16) being slidingly attached to a respective surface float (12); reducing the buoyancy of the platform (14) so as to lower it relative to the surface floats (12) with the towers (16) sliding relative to each respective float (12); manoeuvring a vessel to be lifted to a position above the platform (14); and increasing the buoyancy of the platform (14) so as to raise the platform (14) and the vessel with the towers (16) sliding relative to each respective surface float (12).

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-1549753 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 tanks in the platform and a supply of compressed air, to effect the raising or lowering of the platform. The use of so-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 form 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 attached to a respective one of the surface floats.

According to a second aspect of the present invention there is provided 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 attached 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 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 schematic 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 3 is a side view of the floating dock as shown in figure 1;

Figure 4 is a perspective view showing the submersible platform in a partially raised position;

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;

Figure 9 illustrates a further example for attachment of the towers to the surface floats;

Figure 10 shows a further embodiment of the floating dock;

Figure 11 is a partial perspective view of another an embodiment of the invention;

Figure 12 is a partial end view of the embodiment shown in figure 11; and

Figure 13 is a larger scale sectional view of the embodiment shown in figure 11.

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 form. Platform 14 is rectangular in plan view and has a buoyancy tower 16 in each corner thereof. Each buoyancy tower 16 is slidingly attached 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. Platform 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 vertical 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 show the platform fully lowered and figures 4 to 6 show the platform partially raised.

The buoyancy of platform 14 is controlled so as to effect the raising and lowering thereof. This is done by supplying compressed air to the buoyancy tanks of the platform, venting water (e.g. sea water) from the undersides 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 tanks 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 starts 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 platform is partially off-set by the reduced buoyancy of the towers. Moreover, since the towers are attached to the surface floats the platform is always attached 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 tanks, in that they also can be arranged to have compressed air supplied to them and vented from them, hi 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, hi 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 attached to the buoyancy of the surface floats. This arrangement remarkably mitigates the "break-away" phenomenon as described above. The effect in practical tests is very dramatic and renders the stability control of 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 implementation.

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, implementation of the invention can readily be achieved by persons skilled in the art without a range of relative dimensions being proscribed herein. In similar manner; 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 raising and lowering of the platform 14, including dampening of any tendency for lateral or longitudinal 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 for implementing the sliding attachment of the towers 16 with the surface floats 12 is illustrated in figure 7. The longitudinally inward facing vertical surface of each tower 16 is provided with a vertically extending 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 is rotatably mounted on the spindle, longitudinally aligned with float 12. Further, a respective transversely extending bogey wheel 30 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 platform 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 pneumatic tyres can facilitate assembly of the whole (inflate when in situ) and provide an element 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 forces) to the wheels (28,30) - with the addition of a suitable, conventional, braking mechanism. ₍

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 manner 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 tanks of the platform; and/or differential use 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. Lateral 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 smaller boats simultaneously - subject to the size of the platform and the overall weight being lifted.

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 are 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 hold a wheel but instead to hold 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 main 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 platform 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 platform 14 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 if the surface floats 12 were not present.

If the floating dock 10 is designed to allow the upper surface of platform 14 to be raised above the surface of the water then the upper surface of platform 14 and the undersides of surface floats 12 are preferably arranged to mate positively. One such arrangement is illustrated schematically in figure 8. A surface rail 18 is 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 are 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 fully 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 manner. Having switched off all of the machinery 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 surface 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.

Above there is discussed a variation to the arrangement illustrated in figure 7. The variation in question is that of using spindle 26 not to hold a wheel but instead to hold 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. Figure 9 illustrates a further example, whereby the hydraulic ram can be disposed horizontally instead of vertically. Using the reference numerals from figure 7, figure 9 shows the platform 14 in a partially raised position with a significant portion of towers 16 above the surface of the water. Towers 16 are sli^'dingly engaged with surface floats 12, as described above - for example using the embodiment shown in figure 7. A hydraulic ram 32, comprising a cylinder 34 and a spear 36, is positioned horizontally on top of a surface float 12. The cylinder 34 is secured to the float 12 and hydraulic pressure is used to propel the spear 36 out of the cylinder34 or to retract it into the cylinder. As illustrated herein, the free end of the spear 36 is connected by a cable or chain 38 to the bottom of the left hand tower 16 and by a cable or chain 40 to the top of the right hand tower 16. It will be apparent that as the spear 36 is propelled out of cylinder 34 respective forces are applied through cable/chains 38 and 40 which raise the platform 14 relative to the float 12. Conversely, as the spear 36 is retracted into cylinder 34 respective forces are applied through cable/chains 38 and 40 which lower the platform 14 relative to the float 12. Of course, the cable/chains 38, 40 are fed over respective pulleys, through guides etc - as may be appropriate. In another variation the ram 32 is replaced by a hydraulic winch which has a rotatable drum, rotation of which operates the cable/chains 38, 40 with the same effect as that achieved by the ram 32.

A further embodiment of the floating dock will now be described with reference to figure 10. This embodiment of the dock is particularly suitable for use in lifting large catamarans. Modern pleasure boat catamarans with widths of 13 meters or more are now common but removing them from the water for maintenance (anti-fouling etc) can present significant difficulties. Figure 10 is a schematic perspective view of a floating dock according to the present invention wherein the submersible platform 14 is formed of two separate halves 14a. The two halves 14a can be moved apart and brought together by hydraulic rams 42. In figure 10 the surface floats 12 have been omitted for ease of understanding the drawing.

With the rams 42 in their non-extended position the platform 14 may have a working width of, for example, seven meters. In this configuration the dock may be used to lift single monohull boats, or moored when not in use. To lift a catamaran the rams 42 are extended as required, for example so as to extend the total width of the platform 14 out to fourteen meters. With the platform 14 lowered, the catamaran to be lifted is manoeuvred between the surface floats and secured in the same manner as a monohull (eg using mooring pillars provided on the platform). As the platform is lifted each hull of the catamaran is supported by a respective half 14a of the platform. Synchronisation of the lifting force acting on each half 14a of the platform prevents any undue forces being exerted on the rams 42. Of course, the hydraulic rams 42 may be replaced by any appropriate mechanism which allows the two halves of the platform to be moved apart while maintaining a sufficiently robust connection between them. The design can be further varied, for example by forming the platform 14 in three longitudinal sections. Hydraulic rams maybe provided on each side of the central section, so as to push the two outer sections away from the central section and retract them back as required. Obviously this variation could be adapted to be suitable for lifting trimarans.

Following on from the disclosure given above, it has further been recognised that the effect of providing the buoyancy towers is so effective that a floating dock can be fabricated in which the submersible platform is raised and lowered by purely mechanical means, that is with out the use of compressed air being supplied to or vented from buoyancy tanks in the platform. Figures 11, 12 and 13 herein illustrate an embodiment of the invention which does not rely upon the use of compressed air to raise and lower the platform. Figure 11 is a partial perspective view. Figure 12 is a partial end view and figure 13 is a larger scale partial sectional view showing the use of a hydraulic winch to effect raising and lowering of the platform 14 relative to the surface floats 12. The embodiment illustrated in figures 11, 12 and 13 differs from the embodiments disclosed above in that the towers 16 are essentially off-set to the outside of the lateral edges of the platform 14 rather than rising directly above a respective corner of the platform. Furthermore, the towers are received in respective channels 44 set in to the inner longitudinal edge of the surface floats 12. As before, the towers and surface floats slide relative to each other and wheels or rack and pinion mechanisms can be used between the two in essentially the same manner as described before. In the present embodiment, a respective winch stand 46 is provided adjacent each channel 44 and on the upper surface of the floats 12. As shown in figure 13, each stand 46 supports a hydraulic winch 48. Each winch 48 acts on a chain 50 which is connected to the bottom of the respective tower. The stands 46 position the winches some distance above the upper surface of the floats 12 so as to enable the upper surface of the platform to be lifted clear of the surface of the water.

Considering a hollow air filled surface float which is two meters in width and two and a half meters in height, a buoyancy in excess of four tons per meter length is established. That is a single surface float measuring 2 x 2.5 x 20 meters can be expected to support a load of up to 80 tons before becoming fully submerged. An appropriately sized hydraulic winch mounted on one of the stands 46 can be expected to produce 50 tons of lift (replacement of the winch by a 7 inch diameter hydraulic ram would provide approximately the same lift). Thus, the two surface floats and four winches can generate up to 360 tons of lift. With the dock being fabricated of alloy, the tare can be kept as low as 20 tons, hi theory, the stated size of dock can thus lift a vessel of up to 340 tons gross. Of course, in practice this figure would be reduced in order to provide an appropriate safety margin.

According to this last described embodiment 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 wherein the platform has a pair of buoyancy towers each of which is slidingly attached to a respective one of the surface floats. It will be readily understood from what has been disclosed before that the buoyancy towers are hollow structures filled with gas, preferably air - which may or may not be compressed.

Claims

1. 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 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 it's surface float.

4. A floating dock as claimed in claim 1 , wherein the submersible platform comprises one or more buoyancy tanks and the means for controlling 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 fluid tight manner 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 mating of the upper surface of the platform with undersides of the surface floats as the platform approaches it's fully raised position.

8 A floating dock as claimed in claim 1 , 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 attached 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 platform 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 force between the towers and the floats as the buoyancy of the platform is increased.