Fairey Marine Ltd - Construction Methods

Construction Methods

The hot moulding process was an adaptation to post war boat building of the method originally developed by de Havillands in the 1930′s for “stressed skin” wooden aircraft production, using layers of thin birch plywood sandwiched together with glue over a male mould and “cooked” in a large oven called an “autoclave” By using true mass-production techniques, Fairey Marine were able to turn out vast numbers of identical boats at an unprecedented quality and price. Moulds were constructed from spruce, built up on a steel base plate. Seven by three inches planks cut to the waterplane sections provided the starting point. Working from the shearline, the planks were built up in a series of steps, arriving quickly at a close representation of the designed shape. Subsequent fairing yielded finished dimensions. Rebates for the keel, stem and transom completed the mould building process. Although the veneers used to produce Fairey boats may appear to be parallel sided, every one was in fact profiled. Rather than shaping each veneer to fit on the mould, as in traditional boat building, Faireys saved an enormous amount of time by sawing complete sets of veneers to precision patterns. Veneers were produced in stacks of six. Boat were then typically built in batches of 24 or 36. Early boats used 1/8″ spruce ply, surplus to the War Department’s de Havilland Mosquito aircraft programme. When this material became unavailable it was replaced by 2.5 mm agba veneers.

Chosen for its high gum content, agba formed easily without splitting and glued well. All the dinghy classes used just three agba veneers while some of the bigger boats used up to six. Initially all the veneers were laid at 45° while later boats changed to fore and aft outer planking for aesthetic reasons. With the keel, stem and transom in place, veneers were applied starting on the centreline and working out towards the shear. Each veneer was held in place by just three staples at the keel, bilge and shearline. Roller-application of Borden One-Shot waterproof glue preceded each veneer except the first. With all veneers in place a vacuum bag was drawn over the moulding and secured in place using a clamp plate and G-clamps. Early vacuum bags were made from war surplus barrage balloon fabric. After about 1950, individual rubber bags were prepared on the moulds using uncured rubber sheets which were subsequently vulcanized in the autoclaves used for production. Moulding process and hull repairs

Placed in the autoclave, the vacuum was drawn down to 27/28 inches water-gauge and steam at a pressure of some 50 pounds per square inch introduced. Processing took about 45 minutes at 100°C. Curing at elevated temperatures under vacuum not only ensured that all the veneers were firmly consolidated – a process requiring many thousands of staples using the conventional cold-moulding process – but allowed for the use of a truly waterproof, single part, high-temperature curing glue. During the curing process the glue impregnated the wood resulting in a virtually rot-proof finished shell. Components such as side-decks were also hot moulded while other parts required for assembly were cut to patterns in the same way as the skin veneers. For one of the more complex boats, the International 14, the time for final construction from bare hull to finished boat was set at 230 man-hours compared to 400–500 hours associated with traditional construction.