Building a boat


Gavin Tappenden’s Composite Craft has only ever built one 5.5 Metre and David Hollom has only ever designed one – but the combination’s first co-operation in a Metre boat class swept the board at this year’s international regattas including taking a maiden world championship title. Now the phones have started to ring…


When Peter Morton (Morty) rang me to ask if Composite Craft might be interested in building a 5.5 Metre I found myself saying yes almost before he’d finished ask- ing the question. Such is the rarity of this type of project, and the chance to work with Dave Hollom again assured me we weren’t wasting our time. We’ve worked with Dave a lot over the years, producing many championship-winning boats and


42 SEAHORSE


foils that he has designed. And this was to be a proper campaign with multiple design candidates along with CFD and VPP studies. So while all that was going on we got our teeth into what makes a 5.5m tick. Morty had been competing in the 5.5m


class for a while, so we had access to his older boat to see the scale of the under - taking and the way the sailors interact with the systems onboard. The more infor- mation we were able to glean early on the clearer it made the key decisions on how we were going to build the boat. The first question was easy – all of the


modern 5.5 Metres are built in epoxy/glass foam sandwich construction. This offers the best stiffness-to-weight ratio without going to honeycomb cores which are prohibited by the class rules. There are many ways to build a boat.


Some, like planking over male frames or moulding over male plugs, yield quick results but accuracy will be lost in the building and fairing process. The scale of the inaccuracy depends on the skill on the shopfloor and the expertise of the builder.


Having been involved in America’s Cup


builds when using male plugs accuracies of around 2mm on a 26m boat were deemed acceptable. Dave kindly relayed to us that the paint thickness on the 5.5m was likely to equal around 8kg of displacement, so the possible errors in displacement for male moulded structures could be large. Too large, in fact, for an accurate build


to the very tight displacement target to which Dave had designed the boat. His first 5.5m design was to utilise minimum displacement/minimum sail area on a long waterline. Any extra sinkage of the hull would equate to extra waterline length and therefore take the boat out of class. We’ve always worked to the mantra


that it is the builder’s job to build the boat drawn, not to interpolate or leave the materials used in control of the shape of the boat. That’s a thing of the past. We therefore decided to employ female tools which were taken from CNC-cut plugs. The company we chose to undertake


this work has a great deal of experience in high-accuracy tooling; we were satisfied to


ROBERT DEAVES


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