Projects: Building an 18th century gajeta – Part 2
Part 2: Applying the skin
In a remarkable project that combines traditional boatbuilding skills with modern techniques, a Croatian Gajetareceives its primary wooden framework, cut by computer and bonded with WEST SYSTEM® epoxy.
With the plywood formers for the 7m (21ft) fishing boat assembled at the Betina Shipyard in Croatia (see part 1) the task of attaching the timber frames could begin. The process of creating the structure to ‘form’ the hull is usually known as ‘lofting.’
“As the whole boat was modeled in a 3D programme, this data could be sent to a CNC (computer numerical control) cutter for creating precision components,” said the project’s naval architect, Srdan Dokovic. “Some parts, like the frames, were first bonded together using thickened WEST SYSTEM epoxy to make a strong, shaped piece of timber. This was then trimmed into the required dimensions by CNC.”
At the Betina Shipyard team, the whole project was assembled like ‘a giant Lego set’ as Srdan puts it.
“Every part of the structure was a perfect fit with the next one,” he explained. “Everything on the boat was bonded with epoxy to reduce the amount of metal fasteners required and we laminated several interior components this way as well. With computer modelling, we were able to minimise the amount of mistakes and the CNC machine also gives a big reduction in assembly time. The result is a much lighter, stronger and faster gajeta with minimal waste in man-hours and materials.”
Assembling the frames:
Note: The adhesive is a mix of WEST SYSTEM 105 Resinwith 205 Hardenerand 403 Microfibres Adhesive Filler. This filler is added at a ratio of between 4% to 16% by weight, depending on the thickness required. Alternatively, adding 406 Colloidal Silicainto a 105/205epoxy mix makes an equally powerful adhesive. The ratio required of the 406 Filleris between 3% to 8% by weight.
Primary bonding relies on chemical linking of adhesive layers such as the wet lay-up of fibreglass laminate in a mould. All the layers of adhesive cure together in a single fused layer. Epoxy applied over partially cured epoxy will chemically link with it to form a primary bond. The ability to chemically link diminishes as the previous layer of epoxy cures and the bond becomes a secondary bond.