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Bora Bora 28


This is one of the most interesting processes for amateur construction. The final quality of the boat is excellent, there is no need to build expensive plugs or moulds, and the building technique is quite simple. When the work is completed, the ply-glass boat is absolutely watertight and the final quality is long lasting and requires very little maintenance. A ply-glass hull has all the advantages of fibreglass reinforced plastic and still keeps the warmth and tradition of a wooden interior. Ply-glass boats use plywood as a primary material and hull and superstructure are sheeted with it. After the plywood sheeting is completed a thick glass fibre lamination is applied over the whole hull and superstructure as well. Once deck lamination overlaps hull lamination, the boat is seamlessly encapsulated, giving no possibility to deck-hull joint leakage. Plywood practically only bends in one direction, and doesn't accept compound curves For that matter ply-glass hulls are of chine construction, generating flat segments in transverse sections. When they are more than one chine each side, the hulls are called of the multichine type. If properly designed multichine hulls are as attractive as round bilge hulls and the difference in performance is practically negligible.The method of construction starts with the confection at the workbench of transverse frames and bulkheads and next this transverse structure is put in place over a strongback with the aid of the longitudinal structure of chines, sheer clamps, keel and stem. Following the whole structure is faired and plywood is glued over it. Next, glass-fibre, preferably saturated with epoxy, is applied over the hull which must be built upside down. The lamination isn't merely a protection for the plywood. In the ply-glass method of construction the lamination is strong enough to work as a structural component and once the plywood also has a structural role in the whole process, the result is an immensely strong and rigid monoblock of relatively light construction. To help the overall strength of the structure, all transverse and longitudinal furniture are glued in place collaborating this way for the stiffness of the boat. Internally, two coats of epoxy resin must be applied all over the boat, except in places where a varnish finishing is wanted. In these places the epoxy should be substituted by the chosen type of varnish. The construction by the ply-glass method is simple and requires no skilled knowledge but, once the glass-fibre lamination isn't performed inside a mould, the external surface must be sanded until the surface is smooth enough to be considered a high level of finishing standard. This work is laborious and requires patience mainly to accept the discomfort of glass sanding. But after this task is accomplished, and after all it isn't so difficult to do it, the final result is by far superior than the standard gel coat inishing commonly used in production boats. The ply glass boat is painted instead, using preferably polyurethane, a much better product than the best gel coat available, so ply glass boats tend to have more longevity and no tendency to show osmotic infiltration. A good example of the durability of ply-glass boats is the Multichine 23, Caso Sério. This boat was built in 1980 and despite staying in the water for all this time, she is in perfect condition by far surpassing the state of conservation of most contemporary series produced glass boats. It's important to explain some important points about ply-glass construction that are misunderstood by the less acquainted with the system. The first point that needs to be revised is the idea that wood must breath.This is a fallacy. What breaths is the fungus responsible for dry-rot. When epoxy saturates the pores of wood or plywood, they become impermeable to moisture and oxygen, and rot doesn't occur. For that reason the ply-glass boat as well as a cold moulded hull, should be thoroughly impregnated internally with epoxy. The other point to be considered is the durability of the bonding between glass-fibre and plywood. If plywood is contaminated with grease, paint or humidity bonding isn't good. So it's important that the plywood surface is free from these contaminants. Besides there are two factors that are essential for a good result. The usage of epoxy resin for wetting the glass-fibre, considering the superior bonding properties of the epoxies over poliester resins, and last but not least, the glass reinforcement shall be responsible for an important part in the structure of the boat. Being less important structurally in the process, plywood works primarily as a moulding base, giving no possibility to future delaminations. This is of so great influence in the final result, that even whenpoliester resin is used when glass fibre is thick enough to assure sufficient strength to the structure, there is no possibility of delamination. Taking into account those recommendations ply-glass boats are easy to be built, strong and long lasting, and the process constitutes one of the most successful methods of construction available.