No one denies the need for buoyancy in a dinghy, racing dinghies are full of it, in a cruising dinghy however space is at a premium and most people settle for enough to keep the boat afloat, and then avoid taking any risk liable to cause a capsize.

A capsize would mean most of the gear getting saturated, some lost, probably assistance from another boat, and almost certainly the end of the cruise. I partially solved this problem many years ago by stowing blankets and most loose items in large heavy duty P.V.C. bags, sealed with a clip and lashed under side decks, thwarts etc. In event of a capsize, the trapped air in the bags would then act as buoyancy. Experiments showed that the best way of sealing the bags was to double the end over and use a home made clip similar to that shown in Figure I: - Built in buoyancy has definite advantages but from the stowage point of view has severe limitations. The great problem has always been the watertight access hatch. Either one used small hand size rubber disc hatches which were too small to enable large items to be stowed, and ever then weren't 100% leak proof; or a large hatch which virtually kept only spray out. I have seen large hatches kept tight by the use of dozens of screws or bolts but they took so long to fit or remove that they were almost useless for ready access stowage.

My ultimate inspiration I owe to the close inspection of a door on a pressurised aircraft. The gap is sealed pneumatically. The same effect may be produced using a cycle inner tube as a seal. The principle is illustrated in Fig. II, the inflated inner tube seals and holds the hatch.

One must design the hatch to use standard sizes of cycle inner tube. Any shape of hole may then be cut once the dimension of the perimeter is established provided there are no corners or reverse curves. Care must be taken to render the valve accessible by cutting a slot in the hatch cover (Figure III)

Figure III

Inner tube stretched tight around hatch "wall" when deflated

When ready to seal the hatch the cover is placed in position and the tube inflated with a bicycle pump. To open again just release the valve. Apart from the "L" shaped coamings, no further stiffening of hatch or cover is required. The tube should not be left inflated for long periods as sticking may occur. Since hatches are usuaIly left open for ventilation this should not happen.

Slot cut in cover wall to give access to valve.

Figure IV - suggested shape of hatch openings :-