GB2160481A - Buoyancy tube assembly for marine craft - Google Patents

Abstract

Upstanding edge 15 of a rigid hull has a rubber or like member 16 bolted thereto by bolts 22 passing through spaced parallel extensions 20 and bearing on the extensions by load-spreading metal strips 21. The member 16 has an inboard leaf 18 and an outboard leaf 17 adhered at 19 by their upper surfaces on the lower part of an inflatable buoyancy tube. If desired the member 16 can be replaced by separate inboard and outboard strips. <IMAGE>

Description

SPECIFICATION Buoyancy tube assembly This invention relates to small marine craft of the type fitted with inflatable buoyancy tubes, such as inshore rescue craft, military assault and support craft, vessels used as ancillaries to oil-rigs, or var ious sport or leisure craft.

A well-known type of construction for such ves sels is part-rigid and part-inflatable. In such a con struction a lower hull portion is of a shallow V shape in section to provide handling in rough water. Large inflatable buoyancy tubes are perma nently attached to the ends of the V-shape, i.e. to run along the sides of the vessel, being joined to gether at the bows but leaving the stern free for the attachment of outboard motors. This invention is concerned with an improvement to the attach ment of the rigid hull portion to these inflatable tubes.

Hitherto, attachment has been by adhesion. As described more fully below, strips of material are glued to extend along the tubes and are then ad hered both outboard of the upper edge of the hull and to the top of that upper edge by suitable adhe sives. Typically, the upper edge is somewhat out wardly directed to provide a larger adhesive seating for the tube.

In the extreme conditions of stress and impact encountered by such vessels in use the adhesion eventually fails. Typically, the bows are a source of initial failure, which then progressively works along the sides. However, failure can also start in the middle region of a longer side section.

The present invention is concerned with the se curity of this attachment, which should be able to resist even the most extreme conditions of use in view of its incorporation in life-saving or military craft which need an all-weather capability.

We have now discovered that this crucial attach ment between the rigid and flexible portions can be achieved by a modification of the shape of the hull edge and by associated positive mechanical means anchoring the tubes along their length. Al though to some extent the attachment is more lo calised than the large adhesive areas hitherto used (and might thus be counter-indicated) it in fact lends itself to a different arrangement of the com ponent parts and is less likely to allow separation to begin.

In one aspect the invention consists in an assem bly of a buoyancy tube to a marine craft, compris ing: an upstanding edge to the hull; an outboard flexible member or portion glued to extend along at least the lower part of the outboard face of the buoyancy tube and extending down over the outer face of the upstanding edge; an inboard flexible member or portion glued to extend along at least the lower part of the inboard face of the buoyancy tube and extending down over the inner face of the upstanding edge; and load-spreading clamping members clamping the inner and outer members -to the upstanding edge under the action of bolts passing at intervals through the whole assembly.

Possibly two separate flexible members, e.g.

laminates of heavy duty reinforced rubberised fabric or the like could be used. More preferably, however, a single unit with separate flexible portions, fitting over the edge with its lower regions on to either side is envisaged. Such a unit can be of heavy-duty laminated rubberised fabric or like construction, but it is also envisaged to embody the unit as a rubber moulding (possibly internally reinforced) with the necessary side portions for attachment.

The glued attachment extends across the base region of the tube (usually) at least a little way up the sides. It should not extend so far up that overall flexibility, e.g. for protection when bringing the vessel alongside another, is sacrificed. Usually, it will extend further up on the outboard side of the tube.

Each bolt passes successively through the outer load-spreading member; the lower part of the outboard flexible portion or member; the upstanding edge of the hull, drilled at intervals (e.g. 15 -30 cms) for that purpose; the lower part of the inboard flexible portion or member; the inner loadspreading member; and of course a suitable washer and tightening nut. Although securing takes place only at the intervals, no damage occurs under extreme load or impact. The load-spreading members probably assists this property. They can be separate e.g. as relatively large circular metal (or stiff rubber) discs. Preferably, they are in the form of two strips again for example of metal or stiff rubber, one inboard and one outboard, drilled at the necessary intervals, and common to all the bolts.

In the totality of the vessel different assemblies falling within the above general definition can be used. Thus, some portions of the total assembly can be secured as bolted laminated adhesive strips, as discussed above. Others can be secured by a one-piece heavy-duty rubber moulding. This latter is especially useful for securing the bow and transom regions, which can advantageously be provided with shaped bolt-on one-piece mouldings adhered to the tube as necessary.

Although the invention has been defined above as an assembly of component parts, it is also intended to include within its scope both (a) that sequence of manipulative steps necessary to form the assembly and bolt it into place and (b) the component flexible member, especially the twoportion member, as a modification or replacement article of commerce.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a general diagramatic view of a marine craft fitted with buoyancy tubes, Figure 2 is a diagram showing the prior art assembly of the buoyancy tubes to the rigid portion of the hull, Figure 3 is a diagram showing one embodiment of assembly according to the invention, Figure 4 is a diagram showing another embodiment of assembly according to the invention, Figure 5 shows diagrammatically an extreme in ward distortion, and Figure 6 shows diagrammatically an opposite extreme outward distortion.

A typical inshore rescue craft 1 has a rigid parthull 2 of a shallow V-section and buoyancy tubes 3 attached around the bows and along the sides of the hull but leaving the transom 4 free to accommodate two outboard motors side by side. Typically, the ends of the buoyancy tube 3 are tapered at 5 and extend aft to protect the motors to some extent. Conventionally, the buoyancy tubes can possess a number of separately inflatable sections 3a, 3b, 3c, 3d; rubbing strakes 6 of rubbery material; handgrips 7; and restraint bands 8 against overinflation.

Such a tube is attached to upper edge of the hull 2 as shown in Figure 2. The edge of the hull 2, which may be made of glass-reinforced polymer, is shaped as at 9. The buoyancy tube 3, typically a double envelope of neoprene (inner) and "HYPA LON" (outer), and of generally circular cross-section, rests on the shaped edge. An outer rubber fabric strip 10 is glued to the outboard side of the tube and to the outboard (under) side 11 of the edge 7, the adhesive layer being referenced at 12.

The adhesive layer 12 generally covers the top of edge 7 and also adheres the inboard side of the tube to a second strip 13 of material, which may itself be gusseted and which is adhered to the top of edge 7 at the inboard margin 14.

Under extreme conditions of load or impact, the internal adhesion 13114 tends to become destroyed, probably by outward deformation of the tube pulling open the adhered gusset.

It will be appreciated that Figure 2 is a diagram only and that in particular various thicknesses of layers have been exaggerated for clarity of illustration. Figures 3 to 6 are similarly diagrammatic.

Figure 3 shows in cross-section one possible embodiment of the assembly according to the present invention.

The hull 2 has an edge 15 which extends upwards rather than outwards. Over this edge fits a heavy-duty rubber moulding 16, which may be internally reinforced if desired. Moulding 16 has an outboard leaf portion 17 and a somewhat shorter inboard leaf portion 18. These leaves, or strip portions, are adhered to the buoyancy tube 3 by a layer of adhesive 19.

The moulding also possess two like parallel downward extension or strips 20, spaced to accommodate the edge 15 as shown. Along each such extension is a metal strip 21. At intervals (e.g.

25 cm) holes are formed through strips 21, extensions 20 and edge 15 and are aligned to receive a bolt 22 with head 23 outboard and tightening nut 24 inboard.

When assembled, the components give a structure resistant to extreme impact or load. The Applicants do not wish to be bound by any theory as to the reason for this but believe that the spreading of the "attachment" load by the strip 21, and the geometry of the adhered portions, under distortion, as discussed below, jointly contribute to this advantage.

The widths of portions 17 and 18, relative to the tube or to each other, can vary, the main consideration being that no undue loss of tube deformability should occur. Similarly, the moulding can be embodied over a wide range of shapes and sizes, e.g. for a width W of the edge from 5 to 100 (more usually 15 to 70) mm, depending on the type of craft.

Figure 4 shows a variant embodiment in which as far as possible the same references are used. In this variant two heavy-duty reinforced rubberised fabric strips 25 (outboard) and 26 (inboard) replace the moulding 16. The mechanical engagement with the hull edge 15 (i.e. the bolts, strips, etc) is identical. The adhesive engagement can be separate, as shown, at 27 and 28 along the lower outboard and inboard sides respectively of the buoyancy tube 3.

Figure 5 shows a possible inward deformation of the embodiment of Figure 3. A useful feature is so to dimension the moulding that the head 23 of the bolt is still inboard of the maximum lateral extent of moulding 16 (see dashed line) at this large inward deformation, so that the bolts are protected against impact.

Figure 6 shows a large possible outward deformation of the embodiment of Figure 3.

Both Figures 5 and 6 indicate that even at large deformations the pull on the adhesive is not primarily in an "opening-out" direction (as it is with the inboard adhesion zone of the prior art) but is more or less aligned with the adhesion layer, because the adhesion is always between two flexible parts the geometry of which can vary.

Claims (10)

1. An assembly of a buoyancy tube to a marine craft, comprising: an upstanding edge to the hull; an outboard flexible member or portion glued to extend along at least the lower part of the outboard face of the buoyancy tube and extending down over the outer face of the upstanding edge; an inboard flexible member or portion glued to extend along at least the lower part of the inboard face of the buoyancy tube and extending down over the inner face of the upstanding edge; and load-spreading clamping members clamping the inner and outer member to the upstanding edge under the action of bolts passing at intervals through the whole assembly.

2. An assembly as claimed in claim 1 in which the inboard flexible member and the outboard flexible member are two separate members.

3. An assembly as claimed in claim 1 in which the inboard and outboard flexible members are portions of a single unit fitting over the edge with its lower regions one to either side.

4. An assembly as claimed in claim 3 in which the unit is an integral rubber moulding.

5. An assembly as claimed in any one preceding claim in which the glued attachment extends further up the outboard side of the tube than the inboard side.

6. An assembly as claimed in any one preceding claim in which the load-spreading members are separate circular metal discs.

7. An assembly as claimed in any one of claims 1 to 6 in which the load-spreading members are in the form of one outboard strip and one inboard strip.

8. An assembly as claimed in claim 1 substantially as herein described with reference to Figure 1 or 3 to 6 of the accompanying drawings.

9. A vessel including at least one assembly of a buoyancy tube as claimed in any one preceding claim.

10. A component unit for use in constructing an assembly as claimed in claim 3 or 4, or in claim 6 to 8 as dependent thereon, comprising an internal rubber moulding, shaped to fit on, and with portions located to either side of, the edge and including inboard and outboard flexible members for attachment to a buoyancy tube.