GB2074112A - Improvements in or relating to gas-cushion vehicles - Google Patents

Abstract

A gas-cushion vehicle 1 is provided with a flexible skirt 7 and a system 20 for retracting the flexible skirt so as to reduce drag forces which would otherwise be caused by contact between the skirt and the surface over which the vehicle operates. The flexible skirt 7 comprises a row of contiguous flexible skirt members 15. The skirt retracting system 20 comprises cables 22 extending between adjacent groups of the flexible skirt members and connected to the free end of a net 21 wound round a roller 30. A winch unit 25 is provided to wind up the cables 22 and thus draw the net 21 under the bottoms of the flexible skirt members 15, causing them to collapse upwardly (Fig. 3, not shown). Applicable to an oil-drilling barge which operates as a displacement vessel on water and as a gas-cushion vehicle over land. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gas-cushion vehicles Background to the Invention This invention relates to gas-cushion vehicles, that is to say. to vehicles for travelling over a surface and which, at some time during their operation, are supported, at least in part. by a cushion of pressurised gas, for example air, formed and contained between the vehicle body and the surface. The vehicle-supporting cushion is contained, at least in part, by a flexible skirt.

In the context of the present specification, the term "vehicle" is intended to include both selfpropelled and non self-propelled vehicles.

The present invention may be advantageously applied to a non self-propelled or "dumb" barge used for oil drilling purposes. The barge is transported first over water and then over land to the drilling site using amphibious vehicles.

When the barge is being transported over water, it operates in a displacement mode, that is to say, it travels "off-cushion". During this mode contact between the flexible skirt and the water causes substantial drag forces to be generated.

Object of the Invention The present invention seeks to reduce these drag forces.

Summary of the Invention According to the invention, a gas-cushion vehicle is provided with a flexible skirt and means for retracting the flexible skirt so as to reduce drag forces which would otherwise be caused by contact between the skirt and the surface over which the vehicle operates, the skirt retracting means comprising a flexible sheet disposable between the skirt and said surface and means for drawing the sheet towards the body of the vehicle whereby the skirt is retracted with it.

The flexible sheet preferably comprises a net.

Brief Description of the Drawings An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figures 1A and 1B are respectively, a perspective and a side view of a gas-cushion vehicle, Figure 2 is a fragmentary view, partly in section, of the bow end of the vehicle, Figure 3 illustrates how the bow flexible skirt is retracted, and Figures 4 and 5 are views looking in the direction of the arrows IV and V of Figures 3 and 2 respectively.

Detailed Description of the Preferred Embodiment Referrring first to Figures 1A and 1B, a non selfpropelled gas-cushion vehicle 1 in the form of a dumb barge is shown supported by a cushion 3 of pressurised air formed and contained between the vehicle body 4 and a reactive land surface 2.

The vehicle 1 is used for oil drilling purposes and is provided with a drilling derrick 5 and jib cranes 6.

The rear or stern end of the cushion 3 is contained by a flexible skirt 7 and the front or bow end thereof by a flexible skirt 8 The skirts 7 8.

which are of rubberised fabric. extend laterally at the stern and bow ends of the vehicle body 4 where they are demountably attached to frame structures 9, 10, forming part of the vehicle.

body 4.

Each flexible skirt comprises a row of contiguous independently deflectable, flexible wall or skirt members 1 5 of the form disclosed by British Patent Specification No. 1,043,351. (U.S.

Patent Specification No. 3,420,330 of Bliss corresponds.) In this embodiment, air for forming the vehicle-supporting cushion 3 is provided from an external source, for example, a compressor unit mounted on a service barge. Alternatively, centrifugal fan units may be housed within the vehicle body 4.

With reference now to Figure 2, the vehicle 1 is provided with means 20 for retracting the stern flexible skirt 7 so as to reduce drag forces which would otherwise be caused by contact between the skirt and the surface of water when the vehicle is "off-cushion" and thus in the displacement.

mode. (The usual reason for operating the vehicle 1 in the displacement mode is to conserve fuel which would otherwise be used to run the compressor or fan units and/or to get the vehicle through lock gates.) The means 20 comprise a flexible sheet 21 in the form of a cargo net which is disposable (as shown in Figures 3 and 4), between the flexible skirt 7 and the water surface. The means 20 further comprise cables 22, guide pulleys 23, 24 and a winch unit 25 for drawing the sheet 21 towards the vehicle body 4 whereby, as shown in Figures 3 and 4, the skirt 7 is retracted with it. The winch unit 25 is provided with a brake. (Not shown.) The sheet or net 21 is wound round a roller 30, disposed across the bow of the vehicle 1.The cables 22, which are spaced apart from each other, connect the "free" edge of the sheet 21 with winding drums 31 of the winch unit 25, and, in so doing, extend between adjacent groups of the flexible skirt members 1 5. In this embodiment, each group of flexible skirt members 1 5 comprises three skirt members. (See Figure 5.) The roller 30 is provided with a brake/re-wind unit 32.

With reference to Figures 3 and 4, in operation, to retract the flexible skirt 7, the brake of the unit 32 is released and the winch unit 25 operated to pull the cables through adjacent groups of the flexible skirt members 1 5 and thus draw the sheet 21 off its roller 30, against braking forces applied by the unit 32. As the sheet 21 is drawn off the roller 30, it passes under the bottoms of the flexible skirt members 15, causing them to collapse upwardly. Operation of the winch unit 25 continues until the "free" end of the sheet 21 is adjacent guide pulleys 23, and the skirt 7 fully retracted. The brake of the winch unit 25 is then brought into operation to secure the sheet 21.

To release the flexible skirt 7, the brake of the winch unit 25 is released and re-wind unit 32 is employed to return the sheet 21 to its original position, clear of the skirt 7.

Alternatively, or in addition, the bow flexible skirt 8 may be made retractable in the same way.

Co-pending U.S. Design Patent Application Serial No. 197,428 of Daniel G. W. Turner, filed October 16, 1980, provides a further disclosure of the vehicle 1. Published British Registered Design No. 994,560 corresponds.

Claims (5)

1 . A gas-cushion vehicle provided with a flexible skirt and means for retracting the flexible skirt so as to reduce drag forces which would otherwise be caused by contact between the skirt and the surface over which the vehicle operates, the skirt retracting means comprising a flexible sheet disposable between the skirt and said surface and means for drawing the sheet towards the body of the vehicle whereby the skirt is retracted with it.

2. A vehicle as claimed in Claim 1, wherein the sheet comprises a net.

3. A vehicle as claimed in Claim 1 or 2, wherein the flexible skirt comprises a row of independently.

deflectable flexible skirt members and the skirt retracting means further comprise cables extending between adjacent groups of the flexible skirt members, said cables being attached to said sheet.

4. A vehicle as claimed in Claim 3, wherein the sheet is wound round a roller and the ends of the cables remote from the sheet are connected to winch means.

5. A gas-cushion vehicle substantially as hereinbefore described with reference to the accompanying drawings.