HK1096921B - Floating dry dock system - Google Patents

Description

Floating dry dock system

Technical Field

The present invention relates to a dry dock system for lifting a vessel out of water for maintenance or repair. Typically such types of docks can lift anywhere from one to several hundred tons.

Background

There are basically two types of dry docks. One system includes a ship lock having at least one closeable door in which a ship may be floated and water is drained from the ship lock to raise and dry the ship.

A second type of dry dock system includes a floating dock comprised of rafts that float in a region in front of or behind a vessel and are submerged under the vessel. The raft has a buoyant chamber built into the wall of the raft, where the chamber can be drained with air to clear the water trap. A major problem with these docks is that the required "water level" value makes these docks highly unstable. "water plane" is defined as the area of water that is removed by the dock section at the water-air interface. In general, the greater the "water plane" the greater the stability of the dock. The engagement of the hull with the water provides a significant "water plane" as the dock lifts the vessel out of the water, but becomes particularly dangerous as the "water plane" decreases as the hull rises out of the water (and eventually loses contact with the water). At the end of the lifting operation, the "water plane" decreases rather rapidly and the entire system is extremely unstable, with the considerable weight added to the dock by the vessel leaving the water.

To remain within the limits of stability, dock systems have traditionally been designed to lift the vessel about half the weight of the dock itself.

There is currently a need for dry dock facilities for boats at local ports, berths, club ports or shallow lakes, and the like. There is also a need in the past to provide a design for a floating dock that is less expensive and easier to carry from place to place. It would also be desirable to be able to produce a dry dock system that can be used to lift a vessel out of water quickly, thereby saving valuable time and cost. Conventional dry dock systems do not lift a vessel quickly due to the unstable design described above with respect to the "water plane" problem.

Disclosure of Invention

The object of the present invention is to provide a floating dry dock which is both stable and quick to operate and which can lift a vessel up to twice its own weight.

According to the present invention there is provided a floating dry dock comprising a lifting cradle having two spaced arms pivotally mounted on a floating base, one or more buoyancy tanks interconnecting the arms, and a platform and platform support means mounted on the arms to ensure that the platform remains level when the arms pivot about their pivot means fixed to the base.

Preferably the platform has wheels at its ends and the platform support means comprises an arcuate track on each rocker arm along which the wheels of the platform can roll when the rocker arms are pivoted to maintain the platform at a level.

Preferably the arms are arcuate and a plurality of elongate buoyancy tanks extend between the arms to define part cylindrical cradles.

The base may comprise one or more elongate hulls. For example the base is a catamaran hull. The base may include side walls at each end of the base housing and the pivot about which the rocker arm pivots may be located on an axis between the housings (extending along the length of the housings).

A single floating cradle may be mounted on the base or two spaced floating cradles may be mounted on the base.

The rocker arm may also include an expandable float bath.

According to another aspect of the invention the platform may be pivotally mounted between the arms and the platform support means may comprise pairs of extendable and retractable links, one of each pair of links being extendable and the other of each pair of links being retractable and the links ensuring that the platform remains horizontal relative to the axis pivotally mounted on the arms.

In the latter embodiment, the platform may be generally rectangular, with one of each pair of coupling bars disposed at a corner of the platform and the other of each pair of coupling bars disposed at a respective opposite corner of the platform.

Also in the latter embodiment, the rocker arm may be an elongated arm mounted at one end of the base and having a float disposed at a second end of the rocker arm, with the platform mounted on a pivot at a region intermediate the ends of the rocker arm.

Brief description of the drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 is a schematic side view of a floating dry dock constructed in accordance with the present invention, with two lifting cradles,

fig. 2 shows a partial section through a wheel and a rail via one of the swing arms in the dry dock shown in fig. 1, and

fig. 3 is a side view of a second embodiment of the present invention.

Detailed Description

Referring to fig. 1, there is shown a dry dock 10 having two lifting cradles 11 mounted on a common floating base 12. It will be appreciated, however, that the invention may also be applied to a situation in which only one lifting cradle is mounted on the base. Only one cradle 11 will be described in detail below, but it should be understood that the other cradle 11 is identical or similar, unless the context dictates otherwise.

Referring specifically to fig. 1, the base 12 is an elongated twin-hulled catamaran, fabricated from lightweight marine alloys or steels. The base 12 may be a single hull or a cylindrical float or other floating structure, such as a trimaran.

The engine, propulsion equipment (not shown) and all the control and service components 13 guiding the base 12 to the vicinity of the vessel requiring lifting are placed on the base 12. The service unit 13 includes pumps (to be described later) and other equipment for soaking and evacuating the buoyancy tanks of the lifting cradle.

Each lifting cradle 11 comprises two swing arms 15 pivotally mounted on pivot means 12(a) in the side walls of the base 12. The pivot 12(a) is located on the axis between the two housings of the catamaran base 12 and extends along the length of the base housings. The arms are made of light marine alloy or steel construction and are arcuate and have elongate buoyancy channels 16-20 (shown in dotted lines) extending between the arms 15 to form part of a cylindrical cradle 11 which, when lowered (as will be explained later), encourage the vessel 14 to float in from one end of the cradle 11.

The tanks 16-20 have means for selectively submerging the tanks 16-20 in sequence, causing the cradle to submerge and the swing arm 15 to pivot about pivot 12(a) to become submerged. The buoyancy tanks are connected to a compressed air source 24 so that they can be cleaned of standing water and filled with compressed air to change the buoyancy of the cradle 11. Rocker arm 15 may also include a buoyancy tank (not shown).

The rocker arm 15 has platform support means for supporting a lifting platform 22 in the form of an arcuate guide track arranged along the concave arcuate edge of the rocker arm 15. The lifting platform 22 has at its lateral ends wheels 25 (see fig. 2) running in rails 26. The shape of arcuate guide 26 and the location of wheels 25 on platform 22 are arranged to keep platform 22 horizontal and stable as swing arms 15 pivot about pivot 12 (a).

As swing arm 15 pivots up and down, platform 22 moves horizontally toward or away from base 12 while remaining horizontal.

In order to stabilize the vessel when raising or lowering the swing arms 15, the platform 22 is provided with supports 27 which are spaced apart from each other and fixed to the platform 22 at a distance which is a little greater than the width of the vessel. The height of the supports 27 may be such that they extend above the water (as shown on the left in figure 1) so that the pilot can steer the vessel 14 between the supports 27 when the cradle 11 is submerged in water. The supports 27 are on equal distances on both sides of the plane of symmetry of the platform 22 so that the vessel is located above the centre of gravity of the platform 22 to avoid tilting of the platform 22 when raising or lowering the arms 15.

In operation, the dry dock 10 is floated to a location where the vessel 14 is required to be lifted, or the vessel 14 is floated adjacent to the dry dock 10. The dry dock 10 is positioned in front of or behind a vessel 14. The tanks 16-20 of the cradle 11 are then filled with water to allow the platform 22 to be lowered to a position where the vessel 14 can be floated into, i.e. from one end of the cradle 11 into between the supports 27. This position is shown on the left side of fig. 1.

The buoyancy of the cradle 11 is controllably increased by sequentially pumping compressed air to clear the water traps in the tanks 16-20 as the vessel 14 is placed on the platform 22. First, tank 16 is fed with compressed air, followed by tank 17, which follows tanks 18, 19 and 20 in that order. This causes rocker arm 15 to rise by pivoting about pivot 12 (a). The upward movement of the swing arm 15 from the submerged position shown on the left side of fig. 1 to the position shown on the right side of fig. 1 continues until the vessel 14 is lifted out of the water surface 28.

To lower the vessel 14 from the position shown on the right side of fig. 1 to the position shown on the left side of fig. 1 after repair and maintenance, the above process should be reversed. That is, tanks 16-20 are filled with water in the reverse order, beginning first with tank 20, then sequentially by filling tanks 19, 18, 17 with water, and finally with tank 16.

The combined "water plane" (i.e. the area of the water-air interface) of the vessel 14, the catamaran 12, the arms 15 and the troughs 16-20 remains reasonably constant when raising and lowering the vessel 14, so that the entire dry dock 10 together with the vessel is very stable.

The stability of the dry dock 10 makes it possible to change the conventional safety factor of 2: 1 (that is, the conventional limit for lifting the vessel 14 is half the displacement of the dry dock 10). In this manner, it is possible to lift a ship 14 twice the weight of the dry dock for each dry dock 10 constructed in accordance with the present invention.

In addition, the two cradles 11 shown in fig. 1 may be operated independently of each other. In other words, there is no need to lift the second vessel 14 with another cradle to balance the lifting of one vessel 14. In fact, the provision of two cradles 11 on the catamaran base 12 improves the stability of each, since the overall "water plane" is the sum of the two cradles 11, the base 12 and the vessel 14, and not just the "water plane" of one cradle. In the case of a floating dry dock 10 having two lifting cradles 11, where one cradle is raised and the other lowered as shown in figure 1, the raised cradle 11 effectively converts the catamaran base 12 into a trimaran, the outer hull of which is formed by the raised cradle 11. The overall stability is thus further improved by the use of two lifting cradles 11, since each cradle 11 is very stably activated (compared to conventionally known dry docks).

Two cradles 11 are shown in figure 1 but as explained above, it is not necessary to build two cradles on each base 12.

In the above example, platform 22 has wheels 25 that slide in arcuate rails 26 of swing arms 15. While this is the preferred method of mounting the platform 22, it is also possible to mount the platform 22 on pivots 31 at each end of its axis of symmetry rather than on the arcuate rails 26. This is schematically shown in fig. 3.

Referring to fig. 3, the platform 22 is generally rectangular and the arm 15 need not be arcuate, but may simply be a long arm 15, as shown. In this case the cradle 11 may simply comprise two arms 15, to the free ends of which separate buoyancy tanks 34 are attached.

To maintain the platform 22 in a horizontal, stable position, the corners of the platform 22 are connected to each arm 15 by platform support means (in the form of pairs of coupling rods 36, 37). Each pair of coupling rods 36, 37 may be in the form of hydraulic pistons which are connected to each other to expand or contract the coupling rods 36 and 37 when the arm 15 is raised in a controlled manner by introducing compressed air into the float bath 34 or when the float bath 34 is lowered by flooding, thereby ensuring that the platform 22 remains horizontal throughout all movements of the arm 15. In this case, the centre of gravity of the platform remains at a fixed radius relative to the pivot about which the arm 15 rotates.

Claims (11)

1. A floatable dry dock (10) for lifting a vessel (14) for entry or exit of water, the dry dock (10) comprising a floating base (12) having one or more buoyant hulls, a lifting cradle, characterised in that the lifting cradle has two spaced arms pivotally mounted on one of the floating bases, one or more pontoons interconnecting the arms, and a platform mounted on the arms for supporting the vessel when the vessel is entering or exiting water, and platform support means for ensuring that the platform remains level when the arms are pivoted about their pivot axes fixed to the base, the combined area at the interface between the water surface and the air of the vessel (14), one or more of the buoyant hulls, the arms (15) and the arms remaining substantially constant during the lifting and lowering of the vessel, thereby stabilizing the dry dock.

2. A dry dock according to claim 1 wherein the platform has wheels at its ends and the platform support means comprises an arcuate track on each rocker arm along which the wheels of the platform slide when the rocker arms are pivoted to maintain the platform at a horizontal level.

3. A dry dock according to claim 1 or claim 2 wherein the arms are arcuate and there are a plurality of elongate pontoons extending between the arms to define a part-cylindrical cradle.

4. A dry dock according to claim 1 wherein the floating base comprises a catamaran.

5. A dry dock according to claim 1 wherein the floating base comprises side walls at each end of the base hull and the pivot about which the arms pivot is located on an axis between the hulls extending along the length of the hull.

6. A dry dock according to claim 1 wherein a separate floating cradle is mounted on the floating base.

7. A dry dock according to claim 1 wherein two spaced apart floating cradles are mounted on the floating base.

8. A dry dock according to claim 1 wherein the arms comprise inflatable buoyancy tanks.

9. A dry dock according to claim 1 wherein the platform is pivotally mounted between the arms and the platform support means comprises a pair of extendable and retractable links operable to expand or contract during lifting or lowering to ensure that the platform remains horizontal relative to the axis of pivotal mounting on the arms when the arms are lifted or lowered.

10. A dry dock according to claim 9 wherein the platform is substantially rectangular and one of the coupling bars of each pair is disposed at a corner of the platform and the other coupling bar of each pair is disposed at a respective opposite corner of the platform.

11. A dry dock according to claim 9 or claim 10 wherein the arms are elongate arms mounted at one end on the base and having a buoyancy tank provided at the second end of the arms and the platform is mounted on a pivot at a region intermediate the ends of the arms.