GB2231844A - Maritime emergency escape system - Google Patents

Abstract

An escape system for the evacuation of personnel from a maritime vessel or an offshore platform, such system comprising a normally vertical guide 12 fixed to the vessel or platform so that it passes through the wave effected zone, and a watertight capsule 10 adapted to move through the wave effected zone while being constrained by the guide and to be released from that guide beneath the wave effected zone, said capsule having means to secure it near the top of the guide, a closable entrance into an upper part of the capsule, releasable ballast 18 at or near a lower part of the capsule, and propulsion means to drive the capsule horizontally when released from the guide. <IMAGE>

Description

EMERGENCY ESCAPE SYSTEM SPECIFICATION The invention relates to emergency escape systems from maritime vessels and offshore platforms.

Although davit-launched lifeboats have been installed on ships and offshore platforms for many years, such lifeboats suffer disadvantages as a means of emergency escape because the life boat is suspended vertically during launch, which assumes the platform or ship is on an even keel. Ships or floating platforms will frequently list at a steep angle before sinking. In any case the suspended life boat is subject to wind forces during launch. After launch, the lifeboat is in danger of being capsised by an unreleased davit line, or could be driven against the vessel or offshore platform by large waves.

Skilled, energetic and cool action is needed after launch and release to navigate the lifeboat clear of the vessel or offshore platform. Once clear, a lifeboat in heavy seas continues to be very unpleasant and unsafe.

Rescue of persons from the lifeboat in a heavy sea when both life boat and rescue ship are moving is very dangerous and difficult; rescue from a helicopter is feasible but also very dangerous due to motion of the lifeboat and risk of snagging the lift harness.

The failure of several lifeboats on the 'Titanic', a new ship in calm sea conditions, is a classic illustration of difficulties that can be experienced with davit launched lifeboats.

Most deaths after abandonment of vessels are due to exposure and cold (hypothermia) so modern lifeboats are enclosed. This reduces exposure to the elements but can greatly increase the effects of sea sickness because of the surface motion of the vessel and physical confinement within a crowded interior, without views of the outside world.

Modern survival capsules on oil and gas platforms can be released from within.

This can remove the need for a deck crew, but introduces other mechanisms that need to work faultlessly and require considerable judgement of the correct time to release.

The problem of a lifeboat colliding with the platform however remains unaltered, being greater for some offshore production platforms which, unlike a ship, have no sheltered or 'lee' side.

Recent experience supports this concern. When the 'Alexandra Keilland' semi-submersible sank on 27th March 1980, two of the seven lifeboats were never launched, three were crushed against the structure before release, and of the remaining two which were launched, one was inverted and needed to be righted in the water. When the 'Ocean Ranger' semi-submersible sank on 15th February 1982, two of the four lifeboats were never launched, and the other two were severely damaged during the 21 metres descent. The most successful of these cleared the rig and motored to a standby ship only to capsise during attempts to rescue the survivors, all of whom were lost. When the 'Piper Alpha' platform was destroyed on 6th July 1988, a number of personnel died inside the accommodation module. This indicates that an easily accessible launch device is essential to save lives.

In general, the record of survival craft is not good. In some cases lives have been lost during practice exercises, and the preferred method of escape from North Sea installations is by helicopter. However, situations may occur when helicopters either cannot be flown due to weather conditions, cannot approach the platform due to a fire, cannot land due to the abnormal list angle of the helideck, or cannot arrive in the time and numbers needed to evacuate all personnel before the vessel or platform sinks or is otherwise destroyed.

An independent means of escape is therefore needed, which does not expose persons to the sea or the elements; requires no mental or physical effort or judgement either before, during or after release; does not depend on the activation of mechanisms, starting of engines, setting of controls, and the unaided cooperation of all persons (who may be exhausted, frightened and/or confused) before launch; and will deploy the craft reliably irrespective of the motion and angle of list or keel of the vessel or platform, and of the strength of the wind or height of the waves.

The escape method also needs to be easily accessible to the crew of the vessel or platform, insensitive to abnormal angles of list, and to be able to operate irrespective of wind, waves, or the presence of debris or burning oil on the water.

The proposed escape system, by avoiding the sea surface and use of any free suspension mechanism, but depending on gravity, can meet all these requirements. The system is described in the following section.

The invention provides an escape system for the evacuation of personnel from a maritime vessel or an offshore platform, such system comprising a normally vertical guide fixed to the vessel or platform so that it passes through the wave effected zone, and a watertight capsule adapted to move through the wave effected zone while being constrained by the guide and to be released from that guide beneath the wave effected zone, said capsule having means to secure it near the top of the guide, a closable entrance into an upper part of the capsule, releasable ballast at or near a lower part of the capsule, and propulsion means to drive the capsule horizontally when released from the guide.

In one form the capsule is generally cylindrical and is disposed on the vessel or platform with its axis vertical.

In another form the capsule is inclined up to about 20 degrees to the vertical at all or the lower sections of its passage down the guide.

It is preferred that the guide comprises a rail or wire to which the capsule is connected at two spaced apart points.

It is further preferred that the guide comprises at least two rails or wires which are arranged to constrain the capsule.

It is preferred that the guide is a chute or shaft of substantially constant cross section and the capsule has a correspondingly smaller cross section so that it is constrained by the chute or shaft.

In this preferred form the guide may be an open lattice chute.

Alternatively the guide may be a closed shaft which is accessible only from its upper and lower ends.

The releasable ballast may be suspended beneath the capsule by a cable or chain, in which case the releasable ballast may be disconnected from the capsule when the releasable ballast comes into contact with a seabed or other obstruction beneath the capsule.

The releasable ballast may be disconnected from the capsule when the capsule has sunk to a predetermined depth.

The capsule may have additional ballast for stability purposes and such additional ballast may consist of batteries located at a low point on the capsule.

Advantageously at an upper part of the capsule there is/are radio/visual beacons to aid in identification for rescue services.

In one form there are mechanical thrusters for sideways propulsion.

Alternatively there are hydrodynamic devices to cause it to sink in a controlled inclined path.

There may be one or a plurality of guide members so designed that the capsule and its guide mechanism can be suspended from the davits of an existing lifeboat or survival craft installation, the conventional craft being replaced in this application by the invention disclosed with little or no major structural alteration to the vessel or platform.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically the system in use to effect the evacuation of a semi submersible drilling vessel, Figure 2 shows a similar sequence of events in deepsea water, Figure 3 is a more detailed diagrammatic illustration of a safety capsule installed in a vessel.

Figure 4 is view looking onto the side of a vessel showing another safety capsule, and Figure 5 is a side view of the configuration shown in Figure 4.

The description relates to a semi-submersible offshore drilling platform, but the concept can be applied equally well to a fixed offshore platform or mono-hull vessel.

As shown in Figure 1, the system comprises, in principle, a vertical cylindrical capsule 10 which crewmen can enter at deck level 11, and which, when released, will slide down a vertical shaft 12 in the manner of a diving bell to be released well below the surface (or waterline) and hence below the most severe wave action. The capsule 10 will remain in a vertical plane, continuing its decent on an inclined path which will displace it clear of the platform 14. At a preset depth, ballast 15 will be released and the capsule, still vertical, will return to the surface at 16 where, by reason of its shape, it will float in a stable attitude, like a buoy, with very little roll or pitch and a very damped heave motion. Final recovery of the crew could either be by helicopter winching, from a hatch at the top, or the entire floating unit could be towed to safer waters.

The capsule 10 (shown in more detail in Figure 3) is approximately 2 metres in diameter and 11 metres tall, such that about 50 men can be accommodated on 3-4 levels 17. They remain standing or seated on small saddles in the upright position. No straps are needed. The walls are either GRP, concrete/steel composite or other structures which are good insulators and resistant to hydrostatic pressure at the local water depth with appropriate safety factors.

The capsule is positioned in shaft 12, or on guide rails, such that it is firmly restrained at the wave zone and released as far beneath the surface as possible. Descent is by gravity using a large anchor mass (18 in Figure 3) which may be stowed below water level to improve the stability of the vessel.

The only action from the occupants is to release a supporting mechanism and allow the mass to pull the capsule down and clear of the structure.

Hydrodynamic devices give the capsule a sideways velocity as it descends, so carrying it away from the vicinity of the platform.

A hydrodynamic device to create sideways force can take the following alternative forms: a set of rotating cylinders projecting from opposite sides of the capsule, powered by batteries which operate on the Magnus rotor principle and create a substantial side force in relation to the vertical velocity component of the capsule; a set of inclined vanes or similar hydroplane type devices; or a drogue suspended from the top of the capsule designed to give it an inclined descent.

Subsequent events are shown diagrammatically in Figures 1 and 2. For water depths exceeding 100 metres (Figure 2), the capsule 10 will continue to a preset depth at which the anchor mass 15 will be automatically released and the capsule will ascend. During the ascent, the hydrodynamic devices will continue to incline the capsule path away from the abandoned vessel. In water depths less than 100 metres (Figure 1), the effect of gravity may need to be supplemented by lateral thrusters to displace the capsule sufficiently clear of the platform before the anchor mass touches the bottom and is released.

Where the depth is little more than the column height of the platform the mass may be attached directly to the base of the capsule. Alternatively mechanical means may be provided for connecting the capsule and the weight prior to launch.

In either case, the capsule will return to the surface where it will float in a stable vertical attitude due to its shape. A mast can then be erected to provide fresh air and mount a light and radio beacon. Individuals who suffer from confinement can climb to the upper level which will allow a view outside and in moderate conditions the opportunity to stand on the top.

If the capsule was launched in the correct preset direction, it will be in no danger of being blown or drifted back onto the platform and no corrective action will be necessary. If danger is present however, then the capsule thruster power could be used to redirect the track of the capsule through the water. This is the only stage in the escape when someone on board may need to exercise judgement and take a positive action to improve the chances of a successful rescue.

The stable floating attitude will make a winch recovery of personnel by helicopter, or attachment of a towline by a rescue vessel, simpler to perform than it would be for most other floating body configurations.

The capsule systems comprising electric thrusters1 drive batteries, automatic direction control, hydrostatic release mechanisms and life support are well proven, reliable items of equipment. The capsule configuration is the preferred shape for compressive pressure loading and well within current fabrication experience using either composite materials or metals.

The hydrodynamic behaviour of the capsule underwater and the hydrostatic characteristics when floating at the surface are well understood and can be reliably verified by model basin tests.

The main development areas are therefore expected to be to ensure that the weight of the entire system does not adversely affect the platform stability or payload, when compared with present survival craft; to achieve an access layout that will enable 30-50 men to enter the unit without the first occupants impeding or preventing the rapid entry of others; and the efficient design of comparatively large access doors on a cylindrical pressure hull.

The most severe operational risk is expected to be the psychological effect of a crowded enclosure, known to be underwater, on crew members who are under severe shock when they enter. Confinement has been shown to bring on panic, which is particularly contagious in such a confined and crowded space.

Furthermore, certain individuals are unable to tolerate a 'submarine' environment.

Such factors are not insurmountable and need not prevent the project producing a successful system because the objective is survival when there is no realistic alternative. In such situations men have jumped off 15-30m deck heights into the sea below. The confinement and apprehension would be equally serious in a conventional covered lifeboat, particularly a free fall lifeboat.

No violent motions are expected and hence no body restraint straps are needed.

Groups in different levels can be isolated. The interior of the capsule will be a controlled environment with colour, design, wall texture and sounds designed to suggest security and minimise mental/physical effort or distress.

Human factors engineering, operators' viewpoints and personnel selection and training requirements will be given high priority throughout the project.

The fundamental advantages of the concept are that the persons rescued are never exposed to the elements. No physical agility or mental effort is required, in fact, the occupants need take no action after release. The motions that lead to seasickness in conventional boats are minimised. There is no risk of impact between the capsule and the platform structure.

It is desirable that the aforementioned invention be also incorporated into existing vessels, platforms or allied maritime or offshore installation without the need to modify the structure of the vessel or platform. This will be accomplished by provision of a support structure and set of guide rails that can be suspended from the existing davits used to support the conventional lifeboats or survival craft currently installed.

Referring to Fig 4 the escape capsule 10 will be constrained in guide rails or tubes 21 by guide runners 25. The clearance and compliance in these runners will permit substantial variation in the track gauge or separation distance between the rails, as may be caused by damage and deterioration in service, without risk of the motion of the capsule being impeded. The rails will be suspended from a support structure 22 such that the complete assembly is suspended from existing davits 24 intended to support a conventional lifeboat or survival craft 26. Additional structural restraint will be provided closer to the waterline depending on the existing structure, anchorage points and route into the water.

Personnel will enter the capsule via a staging or walkway 27. This application lacks the advantage of providing an escape route near to the accommodation and main work areas, but enables the other advantages to be provided on a vessel or platform that would otherwise not have the device.

Claims (18)

1. An escape system for the evacuation of personnel from a maritime vessel or an offshore platform, such system comprising a normally vertical guide fixed to the vessel or platform so that it passes through the wave effected zone, and a watertight capsule adapted to move through the wave effected zone while being constrained by the guide and to be released from that guide beneath the wave effected zone, said capsule having means to secure it near the top of the guide, a closable entrance into an upper part of the capsule, releasable ballast at or near a lower part of the capsule, and propulsion means to drive the capsule horizontally when released from the guide.

2. A system as claimed in Claim 1 in which the capsule is generally cylindrical and is disposed on the vessel or platform with its axis vertical.

3. A system as claimed in Claim 1 in which the capsule is inclined up to about 20 degrees to the vertical at all or the lower sections of its passage down the guide.

4. A system as claimed in any one of Claims 1 to 3 in which the guide comprises a rail or wire to which the capsule is connected at two spaced apart points.

5. A system as claimed in Claim 4 in which the guide comprises at least two rails or wires which are arranged to constrain the capsule.

6. A system as claimed in any one of Claims 1 to 3 in which the guide is a chute or shaft of substantially constant cross section and the capsule has a correspondingly smaller cross section so that it is constrained by the chute or shaft.

7. A system as claimed in Claim 6 in which the guide is an open lattice chute.

8. A system as claimed in Claim 6 in which the guide is a closed shaft which is accessible only from its upper and lower ends.

9. A system as claimed in any one of the preceding claims in which the releasable ballast is suspended beneath the capsule by a cable or chain.

10. A system as claimed in Claim 9 in which the releasable ballast is disconnected from the capsule when the releasable ballast comes into contact with a seabed or other obstruction beneath the capsule.

11. A system as claimed in any one of the preceding claims in which the releasable ballast is disconnected from the capsule when the capsule has sunk to a predetermined depth.

12. A system as claimed in any one of the preceding claims in which the capsule has additional ballast for stability purposes and such additional ballast consists of batteries located at a low point on the capsule.

13. A system as claimed in any one of the preceding claims in which at an upper part of the capsule there is/are radio/visual beacons to aid in identification for rescue services.

14. A system as claimed in any one of the preceding claims in which there are mechanical thrusters for sideways propulsion.

15. A system as claimed in any one of claims 1 to 13 in which there are hydrodynamic devices to cause it to sink in a controlled inclined path.

16. An escape system as claimed in any one of claims 1 to 15 but with one or a plurality of guide members so designed that the capsule and it's guide mechanism can be suspended from the davits of an existing lifeboat or survival craft installation, the conventional craft being replaced in this application by the invention disclosed with little or no major structural alteration to the vessel or platform.

17. A system substantially as here in before described with reference to and as shown in the accompanying drawings.

18. A maritime vessel or offshore platform having a system according to any one of the proceeding claims.