GB2277718A

GB2277718A - Survival - craft launching

Info

Publication number: GB2277718A
Application number: GB9309257A
Authority: GB
Inventors: James Dean
Original assignee: Survival Systems International
Current assignee: Survival Systems International
Priority date: 1993-05-05
Filing date: 1993-05-05
Publication date: 1994-11-09
Also published as: GB9309257D0

Abstract

A survival-craft, such as a survival capsule 10, is suspended by a single cable from a winch 16 mounted on a marine structure 11. The capsule has a hull 12 together with a super-structure 14, the hull being provided with oppositely-directed nozzles 21 and 22. A control arrangement controls the issue of compressed gas from the nozzles 21 and 22, to cause the capsule to turn about its suspension cable, during lowering. A compass senses the heading of the capsule, and provides an input to the control arrangement, so that the capsule may be on a pre-determined heading by the time the capsule is floating. <IMAGE>

Description

SURVIVAL CRAFT LAUNCHING This invention relates to a method of and apparatus for use in the launching of a survival-craft, of the kind defined hereinafter.

It is the usual practice to provide a sea-going vessel or a marine structure (such as an oil drilling rig or an accommodation platform) with emergency escape craft for personnel carried by the vessel or structure.

Traditionally, life-boats and life-rafts have been employed, carried by the vessel or structure above the normal water level and provided with a suitable launching system which lowers the life-boat or raft into the water, when required for use. Most life-boats are suspended from two cables (often referred to as "falls") so that the life-boat may remain substantially horizontal and be lowered in a controlled manner, when required for use.

For many years, so-called survival capsules have been used instead of traditional life-boats; such a capsule is in the form of a vessel having a superstructure (or dome) which encloses a volume in which personnel may be carried. The super-structure has doors or hatches which may be sealed, to protect the occupants from fire and exposure to severe weather, and the capsule is made effectively unsinkable by the hull construction. Though early designs of such survival capsules were circular, when viewed in plan, currently many such survival capsules now are of an oval shape, and are stowed alongside a vessel or other structure, ready for use.

It is known to suspend a survival capsule from a single cable, or fall, and to lower the capsule into the water using that single cable. This overcomes the potential hazard in failing to disconnect or re-hook two suspension cables simultaneously, and also allows a quicker escape since a single cable may be disconnected more rapidly than a two-cable suspension system, as used with a conventional life-boat. However, by having only a single fall, directional control during lowering of a survival capsule is lost, and the heading of the capsule on entering the water is indeterminate. It is a principal aim of the present invention to address this problem.

According to the present invention, there is provided a method of launching a survival-craft (as hereinafter defined) which method comprises the steps of: releasing the survival-craft from an elevated carrier and lowering the survival-craft into the water; sensing the heading of the survival-craft at least during the lowering thereof into the water; causing the survival-craft to point in controlling the issue of fluid under pressure from a suitably-directed nozzle furnished on the survival-craft, the issue of fluid being controlled dependent upon the sensed heading.

In this specification, the term "survival-craft" is hereinafter used to refer to all kinds of marine escape vessel for use for example on a ship or on a marine structure, such as an oil rig, an accommodation platform or the like. The term thus extends to, but is not limited exclusively to, survival capsules, lifeboats and life-rafts.

By utilising the method of this invention, a survival-craft may be caused to point in some particular predetermined heading by the time the craft is in the water and released from its suspension arrangement. In the case of a static structure such as an oil-rig or accommodation platform, the survivalcraft may be caused always to point away from the rig or platform, since the position of the craft with respect to the rig or platform at the time of commencement of launching will be known. In the case of a survival-craft being released from a floating vessel, such as a ship, by the time the survival-craft is floating, it may be arranged to be pointing on a heading at about 900 to the heading which was sensed, at the commencement of lowering of the craft (i.e.

parallel to the ship's heading), so that again the craft will be pointing away from the ship, by the time the craft is floating in the water.

Though this invention primarily concerns methods of, and apparatus for, launching a survival capsule suspended by a single fall system, the invention nevertheless is applicable to other kinds of survivalcraft or escape vessels and may, in appropriate circumstances, also be used in conjunction with lowering systems other than a single fall cable system.

The invention will however in the following be described in greater detail mainly with reference to a survival capsule and a single fall cable suspension system for such a capsule.

Preferably, the survival-craft is provided with at least two oppositely-directed nozzles disposed externally of the craft, and the fluid is caused to issue from one or the other nozzle, dependent upon the sensed heading of the craft as compared to the desired, predetermined heading. In this way, the craft may be turned through an appropriate horizontal angle in whatever direction is required to achieve the desired final heading.

Conveniently, the fluid which is caused to issue from the or either nozzle is a compressed gas, such as compressed air, which may advantageously be stored in a pre-charged cylinder, carried by the survival-craft.

It would however be possible to turn the craft on to the desired heading by utilising some other fluid - for example, a liquid pumped to issue from the nozzle at a suitable pressure, or a gas in the form of the product of combustion of a fuel.

The sensing of the heading of the survival-craft is preferably performed by means of a compass located within the survival-craft itself. Such a compass may take the form of a flux-gate compass assembly, which provides an electrical output indicative of the sensed heading, suitable for supply to a control arrangement for the issue of fluid out of the nozzles. The control arrangement may include a change-over valve, able to direct fluid under pressure to an appropriate nozzle, or to shut off the delivery of fluid, and a controller for the change-over valve, which responds to appropriate inputs from the compass assembly.

The controller may be arranged to operate in a more sophisticated mode, so as to anticipate the pointing of the survival-craft on the required heading following initial turning of the survival-craft by the issue of fluid out of one nozzle, whereby compressed fluid may be allowed to issue out of the other nozzle before achieving the desired heading, so slowing and stopping horizontal angular movement of the survivalcraft as the survival-craft reaches the desired heading. Also, the operation of the controller may be damped dependent upon the deviation of the sensed heading from the desired heading, so as to minimise oscillations of the survival-craft about the desired heading.

According to a second aspect of this invention, there is provided a survival-craft (as hereinbefore defined) which includes a pair of nozzles mounted externally of the craft and facing in generally opposite directions in a substantially horizontal plane; a source of pressurised fluid; means to control the issue of fluid under pressure from the source and out of either of said nozzles; and means to sense the heading of the survival-craft which sensing means provides an output to the control means, whereby the survival-craft may be caused to point on a predetermined heading by the control of the issue of fluid from the nozzles.

Preferably, the survival-craft is provided with a suspension point for a single suspension cable, whereby the survival-craft may rotate about the cable when suspended thereby, during lowering the survival-craft.

Operation of the control means may be inhibited when the survival-craft is stowed ready for use, but is caused to commence operating automatically when the survival-craft is launched, by lowering it on its suspension cable. The survival-craft will thus automatically be caused to point on a predetermined heading, by the time the survival-craft is floating in the water and is released, or is ready to be released, from its suspension cable.

The invention further relates to a safety system for a vessel, marine structure or the like and including a survival-craft together with a launching arrangement therefor utilising a single suspension cable by means of which the survival-craft may be lowered into the water, wherein the survival-craft is provided with means to cause the craft to point on some predetermined heading in accordance with this invention, as hereinbefore described.

By way of example only, one specific embodiment of a survival-craft of this invention, and of a launching method therefor, will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of a survival capsule suspended from a davit forming a part of a marine structure, which capsule is arranged to point on a particular heading during the lowering thereof, in accordance with this invention; Figure 2 is a block diagram of a control system for the capsule; Figures 3 to 6 are plan views on the capsule and davit illustrated in Figure 1, Figure 2 showing the capsule prior to the commencement of launching, Figure 5 showing the capsule at the completion of launching and Figures 4 and 5 showing intermediate stages during the launching process.

Figure 1 shows a known form of survival capsule 10 suspended from a davit 11 which forms a part of a marine structure (not shown) such as an oil-rig, an accommodation platform or the like. The capsule has a hull 12 including an in-board motor unit driving a propeller 13, and a super-structure 14 provided with a plurality of hatches 15 giving access to the interior of the capsule, and which may be closed in a watertight manner. The capsule is suspended by a single cable (not shown) from a winch 16 on the davit 11, whereby the capsule may be lowered from the davit into the water, when the capsule is to be used. Conversely, the capsule may be raised by the winch 16, when the capsule is to be recovered from the sea, and stowed ready for use.

When viewed in plan, the capsule has a generally oval shape and is stowed alongside a loading platform 17 giving access to two hatches on one side of the capsule. Typically, the capsule will therefore be stowed parallel to the length of a side of the marine structure. The davit includes a pair of stabilising arms 18 against which the capsule is winched, when it is stowed, ready for use. The single cable suspending the capsule should be of a torque-balanced, nonrotating type. Despite that, there is still a tendency for the capsule to turn about the cable if there is any wind, and so the heading of the capsule by the time it is floating in the water may be somewhat indeterminate.

It is however advantageous for the capsule to be pointing away from the marine structure by the time the capsule is floating in the water, so that personnel within the capsule may make a rapid departure from a source of potential danger.

In accordance with the present invention, the capsule is fitted with a pair of nozzles 20 and 21 on the super-structure 14 at the stern of the capsule.

The nozzles 20 and 21 are oppositely directed in a substantially horizontal plane, generally tangentially to the super-structure at the stern. Internally of the capsule, the nozzles 20 and 21 are connected through a three-position valve 22 (Figure 2) to a pre-charged bottle 23 of compressed air, the valve 22 normally being closed to prevent the issue of compressed air from either nozzle, but being movable from the closed position to either one of two open positions, where compressed gas is released either from nozzle 20 or from nozzle 21.

A controller 24 for the three-position valve 22 is provided within the capsule 10 and includes a flux-gate compass 25 which provides an electrical output indicative of the heading of the capsule. The controller is pre-programmed by control 26 with a desired heading for the capsule, when the capsule is to be launched. Since the position of the capsule when stowed on the marine structure will be known, the pre programmed desired heading typically should be radially away from the structure, from the known launching position.

The controller 24 includes a driving circuit for the three-position valve 22, which circuit responds to the sensed heading of the capsule and causes the valve to operate dependent upon that sensed heading relative to the pre-programmed desired heading. A sensor 27 detects release of the capsule away from its stowed position, at the commencement of lowering of the capsule, and provides an input to the controller 24 to release inhibition of the operation thereof.

Consequently, as soon as launching is started, the controller will be activated and the valve 22 operated as appropriate.

Referring now to Figures 3 to 6, the capsule 10 is shown in Figure 6 at the commencement of a launching cycle. The capsule is released to fall under gravity, the speed of descent being checked by means of a centrifugal brake acting on the winding shaft for the suspension cable. As soon as the sensor 27 detects release of the capsule away from the arms 18, the controller 24 is activated, and senses that the capsule is approximately 900 to starboard of the desired, predetermined heading. When the capsule is approximately at some pre-determined height above the water level, the three-position valve 22 is thus operated to allow air to issue under high pressure from the port-hand nozzle 20.Depending upon the height of stowage of the capsule on its davit, it may therefore be necessary for the controller 24 to incorporate a timer to introduce a suitable delay before operating valve 22, following detection of the release of the capsule.

As lowering of the capsule continues, the capsule starts to rotate about the suspension cable, turning the bow to port, as shown in Figure 4. As the capsule approaches the desired heading, as shown in Figure 5, this is detected by the controller 24 and the threeposition valve is shifted to cause air to issue from the starboard-hand nozzle 21, to slow the rotation of the capsule about its suspension cable. By the time the capsule reaches the water and starts to float, the capsule should be pointing on the desired heading, as shown in Figure 6. If the desired heading is overshot, or not reached, the valve 22 may be operated by the controller as required, to assist an achievement of the desired heading as quickly as possible, as the capsule is released from its suspension cable and gets under way. Air may continue to be released until the bottle 23 is exhausted, but by then directional control of the capsule should be achieved by utilising the capsule rudder.

Though in the drawings the nozzles 20 and 21 are shown adjacent one another at the stern of the capsule, it will be appreciated that the nozzles may be provided at other locations on the capsule. For example, the nozzles could be provided at the bow, where their radius of operation from the suspension cable may be slightly greater, in view of the engine and driving gear of the capsule being located nearer the stern and the fact that the capsule must be more or less balanced about its suspension point. Of course, more than one pair of nozzles could be provided if a greater angular driving force is required - and in this case, one pair of nozzles may be provided at the stern and a second pair of nozzles at the bow.

Claims

1. A method of launching a survival-craft (as hereinbefore defined) which method comprises the steps of: releasing the survival-craft from an elevated carrier and lowering the survival-craft into the water; sensing the heading of the survival-craft at least during the lowering thereof into the water; causing the survival-craft to point in some pre-determined heading by controlling the issue of fluid under pressure from a suitably-directed nozzle furnished on the survivalcraft, the issue of fluid being controlled dependent upon the sensed heading.

2. A method as claimed in Claim 1, wherein the survival-craft is suspended from and lowered by a single-fall cable suspension system.

3. A method as claimed in Claim 2 wherein the survival-craft is provided with at least two oppositely-directed nozzles disposed externally of the craft, and the fluid is caused to issue from one or the other nozzle, dependent upon the sensed heading of the craft as compared to a desired, predetermined heading.

4. A method as claim in any of the preceding claims, wherein a compressed gas is caused to issue from said nozzle.

5. A method as claimed in claim 4, wherein said compressed gas is stored in a pre-charged cylinder located within the survival-craft itself.

6. A method as claimed in any of the preceding claims, wherein sensing of the heading of the survivalcraft is performed by means of a compass located within the survival-craft itself.

7. A method as claimed in claim 6, wherein a fluxgate compass assembly is employed, which provides an electrical output indicative of the sensed heading, and a control arrangement is employed to control the issue of fluid out of the nozzles, said control arrangement responding to said electrical output.

8. A method as claimed in claim 7, wherein said control arrangement is arranged to anticipate the pointing of the survival-craft on the required heading following initial turning of the survival-craft by the issue of fluid out of a first nozzle, whereby compressed fluid may be allowed to issue out of a second nozzle before achieving the desired heading, so slowing and stopping horizontal angular movement of the survival-craft as the survival-craft reaches the desired heading.

9. A method as claimed in claim 8, wherein the operation of said control arrangement is damped, dependent upon the deviation of the sensed heading from the desired heading, so as to minimise oscillations of the survival-craft about the desired heading.

10. A method as claimed in any of claims 7 to 9 wherein operation of the control arrangement is inhibited when the survival-craft is stowed ready for use, but is caused to commence operating automatically when the survival-craft is launched, by lowering said craft on its suspension cable.

11. A method of launching a survival-craft as claimed in claim 1 and substantially as hereinbefore described, with reference to the accompanying drawings.

12. A survival-craft (as hereinbefore defined) which includes a pair of nozzles mounted externally of the craft and facing in generally opposite directions in a substantially horizontal plane; a source of pressurised fluid; means to control the issue of fluid under pressure from the source and out of either of said nozzles; and means to sense the heading of the survival-craft which sensing means provides an output to the control means, whereby the survival-craft may be caused to point on a pre-determined heading by the control of the issue of fluid from the nozzles.

13. A survival-craft as claimed in claim 11, wherein the survival-craft is provided with a suspension point for a single suspension cable, so that the survival-craft may rotate about the cable when suspended thereby.

14. A survival-craft as claimed in claim 12 or claim 13, wherein said sensing means comprises a fluxgate compass which provides an electrical output to said control means.

15. A survival-craft as claimed in any of claims 12 to 14, wherein means are provided to inhibit action of said control means until the survival-craft is being lowered from a stowed position.

16. A survival-craft as claimed in claim 12 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A safety system for a vessel, marine structure or the like and including a survival-craft together with a launching arrangement therefor utilising a single suspension cable by means of which the survivalcraft may be lowered into the water, wherein the survival-craft comprises a survival-craft according to any of claims 12 to 16.