AU2018425047A1 - Inflatable dry dock - Google Patents

Abstract

An inflatable dry dock for storing watercraft

Description

Inflatable Dry Dock

Field of the Disclosure

This application relates to the field of dry docks for storing a watercraft in situ, where the watercraft is substantially removed from contact with water by removing the water, rather than removing the watercraft.

Background of the invention

When mooring watercraft such as boats, jet skis, and similar floating vessels, it is often desired to reduce direct contact between the hull of the watercraft and the water in which the watercraft floats. One obvious reason for this is to reduce any possibility of the watercraft taking on water, potentially sinking, due to a hole through the hull. For example, through-hull fittings periodically fail, resulting in water entry into the watercraft. If such water entry occurs when the watercraft is not occupied, or if any bilge pump fails, or if the bilge pump is inadequate to the volume of water entering the watercraft, etc., then there is a significant likelihood that the watercraft may sink or be damaged.

In addition to potential water entry problems, in a saltwater environment algae, fungi, barnacles, mussels, and other marine life may attach themselves to the hull of the watercraft and grow there. This growth not only is aesthetically displeasing, but also creates drag which negatively impacts the performance of the watercraft in motion. The results are fuel wastage high maintenance costs, as the vessel must be periodically removed from the water, scrubbed, and re-coated. Barnacles especially cause damage as their cement glands often permeate into the hull of the watercraft over time, resulting in significant repair cost to remove, and repair the damaged portion of the hull. Although the portion of the watercraft below the water line may be coated by a specific covering such as anti fouling paint, which is designed to retard marine growth thereupon, none of these coatings fully prevent marine growth, and themselves may reduce the performance of the watercraft.

Thus, whenever possible, watercraft are expediently removed from the water for storage rather than being kept at a dock in the water. This dry storage technique is often expensive and undesirable especially for larger watercraft. In addition, repositioning the watercraft from the dry storage to the water is time-consuming, potentially dangerous, and financially expensive.

US 8739724, the contents of which is hereby incorporated by reference, discloses an inflatable dry dock which allows for dry storage of a watercraft without removing the watercraft from the water. The dry dock disclosed in US 8739724 comprises an inflatable perimeter float having a port side, a starboard side, and an aft side; and a malleable diaphragm sealed to the port side, starboard side, and aft side of the perimeter float to form a watertight boundary between a watercraft and the water in which the dry dock and watercraft float. The watertight boundary in one form having an inner surface wherein the inflatable perimeter when inflated, and diaphragm in combination are less dense than water, and therefore float. The aft side of the perimeter float in one form forms a gate portion which is selectively deflated so as to be more dense than water, and therefore sink below the surface of the water in which the dry dock floats. The gate remains attached to the perimeter float when deflated, and allows water to at least partially fill the watertight boundary such that a watercraft may enter the watertight boundary through the gate.

Once the watercraft enters the dry dock, the gate portion is inflated, sealing off the vessel from the marine environment. A water pump which is in fluid communication with the inner surface of the watertight boundary then evacuates the water from between the inner surface and the watercraft, leaving the vessel to be stored.

WO2018/026289 discloses a similar dry dock comprising a floor float, allowing for vessels of a smaller than the size of the dry dock, or having a non-uniform hull, and reducing the amount of water to be displaced.

Summary of the Invention

The present invention provides an inflatable dry dock for storing a watercraft, comprising a perimeter float, able to be inflated to define the perimeter of an internal region in which a hull or hulls of the watercraft can sit; and a flexible diaphragm sealed to the perimeter float; the flexible diaphragm and the perimeter float, when in use and fully inflated, together forming a watertight boundary between the internal region and an external region comprising liquid in which the dry dock floats.

The perimeter float comprises a first gate portion, able to be inflated and deflated, and able to sink in the external region when deflated to allow the watercraft to enter and exit the internal region, a second gate portion, substantially opposite the first gate portion, able to be inflated and deflated and able to sink in the external region when deflated, and an intermediate region between the first gate portion and second gate portion, able to remain floating in the external region when the first and/or second gate portions sink.

In one embodiment the first gate portion and the second gate portion can be inflated and deflated independently of each other. In another embodiment the intermediate region is inflatable and is able to be inflated and deflated independently of the first gate portion and second gate portions.

The perimeter float may comprise a single inflatable tube, with the first gate portion and second gate portion separated from the intermediate portion by airtight bulkheads.

Each of the first gate portion, second gate portion and intermediate region may comprise separate fittings for inflating and deflating the portion. The fittings may be connected to a source of compressed air by one or more hoses. In this manner, the first gate portion, the second gate portion and the intermediate region can be inflated and deflated independently of each other. The dry dock may further comprise a bracing means for maintaining the configuration of the internal region when both gate portions are deflated to allow entry or exit of the watercraft. In one

embodiment the bracing means is attached to a first side and a second side of the intermediate region and, in use, is sufficiently rigid to maintain a separation between the first and second sides. The bracing means may be inflatable and may, for example, be continuous with the intermediate portion of the perimeter float, such that it inflates along with the intermediate portion. Alternatively, the inflatable bracing means may have a separate fitting for inflation and deflation of the intermediate portion of the perimeter float.

The first gate portion may correspond to a stern portion of the watercraft, with the second gate portion corresponding to a bow portion. This allows for the watercraft to be driven forwards when entering the internal region and reversed out when exiting. Alternatively the first gate portion may correspond to the bow portion of the watercraft and the second gate portion to the stern. In this case the watercraft may be reversed into the internal region and driven forwards out.

It is further possible that the second gate portion is also configured to allow the watercraft to enter and exit the internal region. In this manner the watercraft is able to enter and exit from either end.

The dry dock can be adapted to the watercraft. For example, the flexible diaphragm may comprise a pocket or pockets to encompass projections from the hull of the watercraft such as rudders, keels and outboard motors. Preferably such pockets are further configured to allow the watercraft to enter the internal region without the hull projections damaging the flexible diaphragm.

The flexible diaphragm may further comprise one or more floor floats which are able to be inflated independently of the perimeter float. In certain embodiments the inflatable floor floats are inflated by way of an inflation hose or manifold. Inflation of the floor floats may be simultaneously or

independently, for example in a sequential manner.

The inflatable dry dock may further comprise a water pump in fluid communication with the internal region, for evacuating water from the internal region. In certain embodiments the water pump is an automatically controlled pump which actuates when there is a substantial amount of water within the internal region, and automatically disengages when there is not a substantial amount of water within the internal region.

In certain embodiments the one or both gate portions further comprise weights. These weights assist in the gate sinking when it is deflated.

In a second aspect, the invention comprises a method of closing a dry dock to form a watertight boundary, as described herein. Such a method comprises the step: a. inflating the first and second gate portion, thereby forming the watertight boundary between the external region and the internal region. In certain embodiments the dry dock may be moored in a current in which one gate portion is upstream and the other is downstream. In this embodiment the upstream gate portion is inflated prior to the downstream gate portion. In certain cases inflation of the downstream gate portion begins prior to the upstream gate portion being fully inflated.

In certain embodiments the method further comprises the step: b. activating a pump to evacuate water from the internal region.

In other embodiments, the watercraft is not within the dry dock and the internal region remains partially full of water.

In a third aspect, the invention comprises a method of removing a watercraft from the dry dock or the invention, the invention comprising the steps of: a. deflating the first and second gate portion; and b. moving said watercraft from the internal region to the external region. In certain embodiments the gate portions are deflated simultaneously.

The methods according to the invention, and especially the inflation and deflation of the gate portions may be automated.

Description of the Figures

A preferred embodiment of the invention is described, by way of example only, with reference to the figures in which:

FIG. 1 is a side view of one embodiment of the dry dock according to the invention.

FIG. 2 is a top or plan view of the embodiment of FIG. 1 .

FIG. 3 is a rear view of the embodiment of FIG. 1 .

FIG. 4 is a front view of the embodiment of FIG. 1 .

Detailed Description of the Invention

In the present description of the invention and in the claims which follow, except where the context requires otherwise due to express language or necessary implication, the word“comprise” or variations such as“comprises” or“comprising” is used in an inclusive sense, i.e. to specify the presence of the stated feature but not to preclude the presence or addition of further features in various embodiments of the invention. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

The present invention broadly relates to an inflatable dry dock with two opposing gate portions. By having two gate portions, moving water is able to enter the dry dock at an upstream end and leave from the other.

Tidal current conditions may render an inflatable dry dock unusable for high flow parts of a tide cycle if only a single (entry) gate portion is used. Similar issues may arise in non-tidal, high current conditions for example on a river. Typically any current above 0.5kph can be disruptive.

If the entry gate is facing the current, the open dock acts a scoop on the moving water causing severe strain on the moorings and dry dock structure and usually a large distortion to the shape of the dock which can trap the vessel or prevent entry. The current can invert the gate, pushing it back under the dock such that it will not return until the tide turns. As the forces involved can be several tons, damage to the fittings on the dry dock such as the weight tubes are possible, as is the inflatable dock being torn apart.

If the entry gate is facing away from the current, the gate will not drop, water will not flood the dock, and the client vessel can neither enter nor leave. If the effect is partial (e.g. the gate drops part way), the dock floor diaphragm may foul the boat propellers and if the operator persists the propellers will destroy the floor diaphragm.

FIG. 1 shows one embodiment of a floating dry dock 20 with a watercraft 22 therein. The watercraft 22 is described as having a forward or bow portion 24, a stern portion 26 which may include a swim step 28, and a keel. Extending from the hull 30 in the illustrated embodiment of a watercraft is a rudder 32 commonly used to steer the watercraft, a propeller 34, and a shaft 36 connecting the propeller to an engine normally within the watercraft 22. Power driven watercraft may also use a stern drive, or outboard engine. Other watercraft such as sailboats may not have a shaft or propeller but may be driven by sails, oars, paddlewheels, water jet drives, or similar propulsion means. There are many watercraft that have no propulsion means of their own, but rather rely on the propulsion means of other watercraft (such as tug boats) to be moved.

The dry dock 20 in one form comprises a forward or bow portion 38, and a stern portion 40 easily seen in FIG. 1 . In FIG. 2, the port side 42 and starboard side 44 can be easily seen and distinguished. Looking back to FIG. 1 , the dry dock 20 of this embodiment generally comprises an inflatable perimeter float, in this case a perimeter tube 46 which may be internally segregated at multiple points by bulkheads 50. In one embodiment, transversely aligned bulkheads 50 within the inflatable perimeter tube distinguish middle portions 54 of the perimeter tube 46, from a rear gate portion 52, which may be selectively deflated and allowed to sink below the water line 56 to allow the watercraft 22 to enter and exit the dry dock 20. The middle portions of the perimeter tube 54 are further distinguished by transversely aligned bulkheads 100 from a forward gate portion 102. Like the rear gate portion, the forward gate portion may be selectively deflated and allowed to sink below the water line 56. The middle portions of the perimeter tube 54 remain inflated substantially constantly thereby forming an intermediate region having a buoyancy sufficient to prevent the dry dock from sinking entirely.

Attached and sealed to the perimeter tube 46 is a flexible diaphragm 58. The perimeter tube 46 and diaphragm 58 together form a watertight barrier between the internal region 96 of the dry dock (shown as including the outer hull 30 of the watercraft 22) and the external region 98 which comprises the water in which the watercraft 22 and dry dock 20 float.

The watertight diaphragm 58 may be formed of polymer impregnated fabric, polymers, watertight or water resistant fabrics or other materials commonly used in the production of inflatable watercraft such as for example polyester reinforced polyurethane. Chlorosulfonated polyethylene (CSPE) synthetic rubber (CSM) commonly sold under the trade name“Hypalon” may also be used. Other materials such as polyvinyl chloride (PVC), polyethylene, polypropylene, and other plastics or plasticized materials may be utilized in both the formation of the diaphragm 58 as well as the perimeter tube 46.

The diaphragm 58 includes inflatable floor floats 90. The floor floats may be formed as part of the diaphragm 58 or may be separately fixed to the internal or external surface of the diaphragm. As best shown in Figure 2, the floor floats 90 are shown as being placed longitudinally along the bow-aft axis of the boat. However, depending on the nature of the watercraft a number of other configurations can be envisaged.

To aid in connection between the dry dock 20 and the watercraft 22, the mooring dock, pilings, another vessel, an anchor, and/or other secure mooring attachment points, a plurality of mooring beckets 60 are provided which allow attachment of mooring lines (ropes) which may then be attached between the dry dock 20 and the watercraft 22, the mooring dock, another vessel, or other apparatus to form a secure attachment between the dry dock 20 and the other apparatus. Generally, the vessel will be attached directly to the mooring dock through other mooring lines to reduce stress on the dry dock 20, although the watercraft 22 may be attached to the dry dock 20 through the mooring lines on a temporary basis while initially docking the watercraft. The mooring beckets 60 may also provide attachment points for electrical connections, fluid conduits for air entry, and water evacuation.

The diaphragm 58 may include a pocket 62, or a plurality of pockets 62, to protect and seal around the rudder(s) 32, propeller(s) 34, and/or shaft(s) 36. Similar pockets may be sized and shaped for outboard motors, sailboat keels, jet drives, and other hull projections.

The dry dock 20 may also comprise a plurality of handles 88, as shown in FIG. 2, for grasping such as for repositioning of the dry dock 20 and/or to act as a fender against the hard and rough faces of the fixed or floating jetties to which the dry dock can be tied.

In one form, the rear gate portion 52, has a weighted portion, such as a weight tube 64 or plurality of weight tubes 64 which may be heavier than water. When the rear gate portion 52 is deflated it will pivot about a gate pivot 66 along pivot arc 68 as shown in FIG. 1 to an open position 70. As shown, the weight tubes 64 may be external of the gate portion of the perimeter tube, or they may be internal. In the gate open position, water may flow into the internal region 96, and the watercraft may be driven or pulled into or out of the internal region 96.

The rear gate portion 52 is raised by pumping air into the rear gate portion 52 through a rear gate inflation hose 72 shown in FIG. 2, which may be coupled to a source of pressurized air through a disconnect fitting 74 either on the watercraft, on the moorage dock, or on (in) the dry dock 20. As the rear gate portion 52 is inflated, it will become lighter than water, pivot about the gate pivot 66 from the open position 70, to a closed position 76 along pivot arc 68. Bulkheads 50 assist in operation of the gate, as they maintain positive air pressure in the forward portion of the perimeter tube 46, while allowing the gate portion 52 to pivot and partially sink below the waterline 56. In certain cases the bulkhead 50 may include a one-way valve allowing air to flow from the rear gate portion to the middle portions of the perimeter tube 54, thereby allowing the air in the middle portions to be replenished as needed when the rear gate portion is raised.

The forward gate portion 102, may also have a weighted portion such as a weight tube 104. When the gate portion is deflated it will pivot about forward gate pivot 106 along pivot arc 108 as shown in FIG. 1 . As shown, the weight tubes 104 may be external of the forward gate portion of the perimeter tube, or they may be internal. The dry dock 20 is further shown as comprising an inflatable bracing tube 110 which is not sealed to the flexible diaphragm 58. The bracing tube 110 may be separately inflated, or inflated along with the middle section 54. Like the middle section 54 the bracing tube 110 is nearly constantly inflated.

The forward gate portion 102 may be raised by pumping air through the forward gate inflation hose 112 shown in FIG. 2, which may be connected through disconnect fitting 114. As the forward gate portion 102 becomes lighter than water, it pivots about forward gate pivot 106 to a closed position

116.

The inflatable bracing tube 110 serves as a bracing means to keep the port side 42 and starboard side 44 from converging when both gates are open. Other bracing means are also possible including using mooring ropes to sustain the gap between the port side 42 and starboard side 44, or other rigid non-inflatable structurs. The bracing tube 110, however, performs two further useful purposes in that it serves as a guide to localise the bow portion 24 of the watercraft, and as a cushion to prevent the bow portion 24 of the watercraft from impacting any dock or other mooring object. The bracing tube 110 can be joined with the two middle portions 54 of the perimeter tube 46, such that air can flow between the three. This enables a single inflation point for the two middle portions and the perimeter tube.

The floor floats 90 can be inflated by air pumped through the floor inflation hose and manifold 92 shown in FIG. 2, which may be connected to a source of pressurised air through disconnect fitting 94. In the depicted embodiment the floor inflation hose and manifold 92 has a separate disconnect fitting 94 for an external inflator although it is possible to have a single connector for the gate portion and floor inflation portions which is selectively operated. The inflation of the floor floats results in the floats becoming lighter than the water in the internal and external regions and thus lifting the flexible diaphragm 58. In most cases this lifting will be restrained by the diaphragm coming into contact with the hull or hulls of the vessel, although the lifting may also be constrained by the connection between the diaphragm and the perimeter float. As a result of this lifting, a portion of the water in the internal region will be forced out through the gate portion in the open position 70.

The forward gate portion 102 and the rear gate portion 52, as well as the floor floats 90 can be deflated by allowing air to flow from the portions or floats, through the inflation tubes 112, 72 and 90 out through an operating valve (not shown). Although not shown, the gate portions may have a non crush air evacuation tube running internally from bulkhead to bulkhead. This allows air trapped on the off side to escape across to the side where the operating valve is situated.

In one form, a first plurality of electrically conductive leads 78 are attached to the inner surface of the watertight boundary (diaphragm 58). These electrically conductive leads are in electric communication with a water pump 82 so as to provide operating power thereto. A second plurality of electrically conductive leads 80 may be attached by an electrical disconnect fitting (not shown) to the first plurality of electrical leads 78 and allows connection of the pump 82 to a power supply on the watercraft 22, or dockside. Manual water pumps may also be used, or the water pump may be inside the watercraft and connected by a tube or through-hull to the area between the hull 30 of the watercraft and the watertight boundary (diaphragm 58).

In one form, the water pump 82, or in some cases a plurality of water pumps, is an automatic, bilge pump which is actuated when in contact with water, and de-activated when a certain amount (level) of water is not present, or which may be controlled by an external load sensing controller. The water pump 82 is normally connected through a tube 84 to an overboard discharge fitting 86, as shown in FIG. 2, which directs the water from the internal region. In another form, the pump is a dockside pump with a suction hose into the internal region 96 of the dry dock. Such a pump may be controlled by a float switch or by an external load sensing controller and may be driven by mains power.

The source of pressurized air may be external of the perimeter float 46, or may be provided within the perimeter float 46. In one embodiment, an air pump (compressor) is provided within the watercraft 22 and the disconnect fitting 74 is mated to an interoperating fitting on the watercraft 22. In this way, air can be pumped into the gate portion 52 and the rest of the perimeter float 46 without a fluid (air) connection to the mooring dock or other vessel. This also allows the apparatus to be completely portable, as it does not rely on shore power or external connections.

When the watercraft is not within the dry dock 20, both the rear gate portion 52 and the forward gate portion 102 are usually in the closed position (76 and 116 respectively) forming a watertight boundary, although it is possible that one or both gate portions remain open. The internal region 96 may remain filled with water, or be partially or fully emptied. The internal region remaining filled with water may have advantages when the vehicle is absent by preventing uplift in the case of strong wind or wave activity. It is thus useful when the boat is absent for long periods and/or storm conditions are expected. However, when the internal region 96 is filled with water, the flexible diaphragm 58 creates drag in any current, resulting in unnecessary stress on the dock. Thus a partially or fully evacuated internal region 96 may be preferable. The order of the opening and closing of the gate portions depends on the direction of the current, rather than whether the gate portion corresponds to the bow or stern of the watercraft, thus the preferred operation of the dry dock will be described below with reference to an upstream gate portion, being the gate portion (forward gate portion 102 or rear gate portion 52) which faces the current, and a downstream gate portion, which faces away from the current.

In order for the watercraft to enter (or exit) the dry dock at least one of the gate portions, which is configured to allow entry and exit of the watercraft, must be lowered. In the embodiment depicted this is the rear gate portion 52. In low current conditions, for example at the turn of the tide, it may be possible to lower only one gate portion to allow for entry or exit of the watercraft. However, in high current conditions both the gate portions can be deflated and therefore lowered.

When deflating both gate portions simultaneously the upstream gate portion is pulled down by the current, causing the water to quickly enter the internal region resulting in the flexible diaphragm and the downstream gate portion being pushed down. This results in much faster flooding of the dock (by maybe 5-10 minutes) than for a single gate, as well as the diaphragm being pushed deeper sooner, to ensure clearance of any propellers. Moreover, because the water is able to flow through the internal region the risk of damage to the dock due to the force of the current may be at least partially mitigated.

Once the watercraft is in position within the internal region, it is necessary to raise the gate portions. By raising the gate portion facing the current first, the flexible diaphragm is pushed up by the force of the current, thereby displacing water contained in the internal region through the downstream gate portion. This effect may be aided by the inflation of the floor floats. The displacement reduces the amount of water required to be pumped from the internal region and greatly decreases the amount of time and energy required to pump the water from the dock.

Once both gate are in the closed orientation and a watertight boundary is established around the watercraft, the pump is actuated and any remaining water between the watercraft and diaphragm is then evacuated. If the pump is an automatic type pump, it may be left on (powered) to evacuate rainwater, water from waves splashing into the internal region or water leaking or otherwise entering this region.

Once the rear gate portion is in the closed orientation it is also possible to deflate the floor floats. The flexible diaphragm is then lifted by hydrostatic pressure into contact with the hull. Alternatively, the floor floats can remain inflated while the watercraft is in position.

In order to allow the watercraft to exit the dock the gates can be lowered in accordance with the procedure for entry to the dock described above.

Once the watercraft has exited the dock the gate portions can then be moved back to the closed orientation. Depending on the whether it is desired to leave the internal region filled with water, or be partially or fully emptied, the sequence of gate inflation can be different. Simultaneous inflation of the gates will result in the internal region remaining substantially full of water, whereas first inflating the upstream gate, with or without the floor floats, followed by shortly thereafter inflating the downstream gate results some of the water being displaced, leaving a partially filled internal region. If it is intended to remove all of the water from the internal region, then it is possible to fully inflate the upstream gate (and floor floats) before inflating the downstream gate and then activating the pump if necessary.

As described above, the steps of inflating a first upstream gate portion, inflating the second downstream gate portion and activating the pump are in one form sequential. However, it will be apparent that the steps could overlap. For example, once the forward gate portion is raised above water level, and provided the rear gate portion remains below the level of the floor floats, the water will flow out of the internal region. Thus the process of inflating the downstream gate portion can begin before the action of inflating the upstream gate portion (or the floor floats is complete).

Alternatively, there may be a delay between the action of inflating the floor floats and inflating the gate portion in order to allow the water to flow from the internal region.

It will be apparent that, by first inflating the upstream gates and floor floats a large portion of the water can be efficiently removed from the dry dock. This water would otherwise need to be pumped out by the pump. In many situations mains power is not available, thus the pump may be required to run on power from the watercraft. In these situations a high volume pump is not needed. The use of the upstream gates and floor floats of the present invention may allow for the use of a low volume pump whilst still quickly and efficiently removing the majority of the water.

When not required, or for transportation, the entire perimeter tube, as well as the bracing tube can be deflated and the entire dock can be folded, thereby minimising the space required for storage or transport.

Whilst the present invention is illustrated by the embodiment depicted, other variations may exist. In the embodiment depicted, the entire perimeter tube is able to be inflated and deflated, which allows for easier transportation. However, the intermediate region of the perimeter float, which remains floating when the gate portions are deflated, could be made of, or comprise another, permanently buoyant material such as closed cell foam fillers, leaving just the gate portions to be inflated and deflated.

While the floor floats are depicted as cylindrical and longitudinal, they may be incorporated in a number of other shapes or orientations depending on the nature of the vessel. For example, the floor floats could be arranged in a substantial V shape around the bow of the vessel, and mapping the shape of the perimeter float, thus facilitating the aft runoff of water from the bow of the dry dock.

Sequential inflation of the floor floats could also achieve a similar effect. By inflating floor floats firstly at the farthest region of the dry dock from the gate portion, and then sequentially inflating floor floats placed incrementally closer to the gate portion, water can be pushed out of the open gate. Such a result can be achieved for example by the use of multiple rows of floor floats. Alternatively the floor inflation hose can be connected to the floor float at the end farthest from the gate portion and the pressure provided can be such that the floor float gradually inflates, with the inflation occurring fastest at the end furthest from the gate portion. In extremely efficient versions of this embodiment it could be envisaged that no pump is required.

Where the watercraft is a catamaran, there is a large cavity between the two hulls, which remains full of a significant quantity of water once the watercraft is positioned in the internal region. By positioning one or more floor floats within the cavity, at least a portion of this water can be displaced by the inflation of the floor floats, leaving less water to be pumped from the cavity. In a certain embodiment a single floor float can be positioned centrally in the internal region, preferably perpendicular to the gate so that it lies between the hulls and when inflated will rise up in the cavity. Alternatively, instead of a single float, multiple floor floats, for example two, can be positioned in a colinear manner. This enables inflation of the floor floats independently, for example to allow for sequential inflation.

Preferably the floor floats are elongate. However, the floor floats may include perpendicular extensions allowing for greater buoyancy and displacement of water. Clearly such an arrangement can be adapted for other embodiments where a cavity is created, for example a trimaran.

The dry dock may also include non-inflatable floor floats, either in addition to, or in place of inflatable floor floats. These floor floats, made for example from non-inflatable closed cell foam fillers, can remain permanently supporting the floor in the central tunnel(s) of multihull vessels.

It will be appreciated that the flexible diaphragm will need to rise (and fall) inside the cavity along with the floor floats. In order to ensure that contact of the diaphragm with the hulls does not restrict this movement, the flexible diaphragm can include an additional drape or extension of material which extends as the floor float rises within the cavity. Such an arrangement may be of use in embodiments other than those which have a cavity between hulls.

The inflation hoses are shown in the embodiment as external to the perimeter tube. However, an alternative is to run these through the middle of the perimeter tube and through the front bulkhead. This has the advantage of preventing damage to externally mounted hoses.

In most cases it will be that the rear gate portion will correspond to the stern of the watercraft.

However, in certain alternatives it may be that the watercraft is reversed into the dry dock, and thus the rear gate portion corresponds to the bow of the water craft. Moreover, it will be apparent that the dry dock can be adapted such that either gate can be used for entry or exit of the craft.

The processes required for operating the dry dock may be performed or controlled manually, or they can be automated. In the preferred operation described above a number of variable operations are available depending on the desired result. Further variation is introduced as the upstream gate may change depending on whether the tide at the time of the operation is an ebb tide or flood tide. Thus it may be beneficial to automate the inflation, deflation and pump operations so that a user only has to determine the state of the tide and select their desired result. Alternatively, even the state of the tide could be taken into account by the automation, for example by way of sensors or by programming in tide timetables. Automation also allows for inflation pressures to be monitored and kept at an optimum. Water pumping can also be sequenced according to whether the gate portions are up or down, or a vessel is present or absent. Thus with automation there need be no disconnects or valves to be manually worked.

Although the dry dock is described above as being moored to a jetty or similar, it is also particularly suited to swing moorings, which are cheap and popular and often situated in tide channels. It is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to the detail and embodiments described above. Additional advantages and modifications within the scope of the appended claims will readily appear to those sufficed in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general concept.

Claims (22)

What we claim is:

1 . An inflatable dry dock for storing a watercraft, comprising a perimeter float, able to be inflated to define the perimeter of an internal region in which a hull or hulls of the watercraft can sit; and a flexible diaphragm sealed to the perimeter float; the flexible diaphragm and perimeter float, when in use and fully inflated, together forming a watertight boundary between the internal region and an external region comprising liquid in which the dry dock floats; the perimeter float comprising: a first gate portion able to be inflated and deflated, and able to sink in the external region when deflated to allow the watercraft to enter and exit the internal region, a second gate portion, substantially opposite the first gate portion, able to be inflated and deflated, and able to sink in the external region when deflated, and an intermediate region between the first gate portion and second gate portion, able to remain floating in the external region when the first and/or second gate portions sink.

2. The inflatable dry dock according to claim 1 , wherein the first gate portion and the second gate portion can be inflated and deflated independently of each other.

3. The inflatable dry dock according to claim 1 or 2, wherein the intermediate region is inflatable and is able to be inflated and deflated independently of the first gate portion and second gate portions.

4. The inflatable dry dock according to any one of claims 1 to 3, further comprising a bracing means for maintaining the configuration of the internal region when both gate portions are deflated to allow entry or exit of the watercraft.

5. The inflatable dry dock according to claim 4, wherein the bracing means is attached to a first side and a second side of the intermediate region and, in use, is sufficiently rigid to maintain a separation between the first and second sides.

6. The inflatable dry dock according to claim 4 or 5, wherein the bracing means is inflatable.

7. The inflatable dry dock according to any one of claims 1 to 6, wherein the first gate portion corresponds to a stern portion of the watercraft and the second gate portion corresponds to a bow portion of the watercraft.

8. The inflatable dry dock according to any one of claims 1 to 7, wherein the flexible diaphragm comprises at least one floor float which is able to be inflated and deflated independently of the perimeter float.

9. An inflatable dry dock according to any one of claims 1 to 8, which further comprises a water pump in fluid communication with the internal region, for evacuating water from the internal region.

10. The inflatable dry dock as recited in claim 9, wherein the water pump is an automatically controlled pump which actuates when there is a substantial amount of water within the internal region, and automatically disengages when there is not a substantial amount of water within the internal region.

1 1 . An inflatable dry dock according to any one of claims 1 to 10, wherein one or both gate portions include an added weight to assist in sinking.

12. A method of closing a dry dock according to any one of claims 1 to 1 1 , the method comprising: a. inflating the first and second gate portion, thereby forming the watertight boundary between the external region and the internal region.

13. The method according to claim 12, wherein the dry dock is moored in a current in which one gate portion is upstream and the other is downstream.

14. The method according to claim 13, wherein the upstream gate is inflated prior to the downstream gate portion.

15. The method according to claim 14, wherein inflation of the downstream gate portion begins prior to the upstream gate being fully inflated.

16. A method according to any one of claims 12-15 further comprising: b. activating a pump to evacuate remaining water from the internal region.

17. A method according to any one of claims 12-16, wherein a watercraft is not within the internal region of the dry dock and the internal region remains partially full of water.

18. A method of removing a watercraft from the dry dock according to any one of claims 1 -1 1 , comprising the steps of: a. deflating the first and second gate portion; and b. moving said watercraft from the internal region to the external region.

19. The method according to claim 18, wherein the first and second gate portions are deflated simultaneously.

20. A method according to any one of claims 12-1 9 in which the operation of the gate portions is automated.

21 . An inflatable dry dock, substantially as herein described or exemplified with reference to the drawings.

22. A method according to claim 12 or 18, substantially as herein described or exemplified.