Left: steered by Laser sailor Elliot Hanson and crewed by Andrew ‘Dog’ Palfrey and Sam Haines, GBR 42 Jean Genie keeps her bow up better than most in a steep chop in Norway to win the 2022 5.5 Metre Class World Championship. The deck (left) and hull tooling are manufactured using a substantial grp laminate, the same materials as used for the boat itself; as well as keeping costs sensible compared with carbon tooling, more importantly this means that the coefficients of expansion are similar between the tooling and the boat’s primary structure, minimising problems when the whole assembly is put into the oven to cure. Note how the vertical topsides are all part of the deck moulding, rather than the hull moulding as in a conventional build. A sharp chine makes this a lighter solution
see the 3D tolerance scans of the moulds they sent us displayed errors of less than 0.3mm. It was this guarantee of accuracy that allowed Dave to push the limits of the rule regarding minimums and maximums and the resulting rating (5.5m). Rather than siting it conventionally at
the sheer, we chose to place our join between hull and deck on the high chine of the hull. This facilitated a lot of the fit-out works to be completed before the join, as well as allowing the deck/hull intersection to be built in one piece so eliminating fairing work high up. This worked well: we built the deck first
so that the dry-fit of all the systems, cleats, rope lengths and electrical system could run concurrent with the hull build. As we suspected some of the areas within the finished hull and deck were going to be impossible to work in, so again we were able to install fittings etc prior to joining. The 5.5m rule includes minimum scant-
ling weights for both hull and deck struc- tures which effectively control the compet- itive longevity of the boats. The rule also controls which materials are allowed in these structures. Only glass fibres of E, R and S types are permitted. We chose S-glass (essentially the same as R) as it is a more refined version of E-glass and exhibits higher stiffness and strength. However, the availability of this fibre is
problematic nowadays. It used to be used by the ballistics industry but they’ve moved on to other materials. It is now fairly rare and so it is expensive. Eventually we man- aged to secure a supply that was made to order from a well-regarded UK pre-preg manufacturer. (For anyone who is not certain, a pre-preg is a fibre – be it carbon, glass, aramid etc – that is impregnated with a resin, epoxy in our case, that will only cure at an elevated temperature. It remains
in an uncured state at room temperatures for up to 30 days, some even longer. It is almost dry to the touch when handling – except on hot days when it can be challeng- ing… It cuts cleanly with utility knives and is low in Volatile Organic Compounds (VOCs). All curing should also occur under vacuum pressure or greater.) We chose to use pre-preg because it allows
very accurate placement of reinforcements and arrives impregnated with the optimal amount of resin for the weight of fibre. In particular, it allows the builder time. Anyone who’s ever been involved in
vacuum laminating using wet epoxy resin, on a large scale, will be aware of the per- sonnel numbers required to ‘beat’ resin curing times without having to break down the process (and thus sometimes the structural continuities) into manageable chunks. If you run out of resin flow-time before the vacuum is applied it means that a higher void content is likely. As you are probably aware, voids are the nemesis of any laminated structure. Unfortunately if you laminate in stages the finished structure will also be heavier because of the excess resin left on the surface at each stage. Suzy Russell of Orca Consulting was in
charge of the structural design and our available pre-preg fibre weights and resin content were relayed to her in good time so that a very accurate laminate schedule could be devised. Both the deck and hull of a 5.5m have samples taken post-build to ensure legality, and we were happy when the finished product came out within a few grams of the minimum scantling weight. It’s a little upsetting to see 40mm holes
that then need repairing drilled in your new boat but rules are rules. The decision to use PVC cores was
based on our experiences of different cores over the years. The 5.5m class rule dictates
that the density of the core used in the hull, deck and structure must be at least 80kg/m3
so this formed the starting point
of some more investigative work. All foam cores are essentially formed by
adding a base chemistry together with a foaming agent that react in a way to create a large block of foamed material; however, the density can vary considerably within the block produced. These blocks go through various processes, but once fin- ished they are cut into the sizes and thick- ness that the customers require. Neverthe- less that original variance in density remains displayed in every cut sheet, so we were keen to try to diminish the potential differences as much as possible. Fortu- nately our chosen suppliers were happy to guarantee a maximum of 5% tolerance with a certificate of conformity (this is not universally the case). Cores were available that exhibited
higher properties but they came with a larger price tag and would also have been harder to use. One criterion for the core chosen was for its ease of thermoforming, since we were keen to pre-shape our cores using the mould before starting the laminate schedule. The core was cut to shape and placed into the mould, vacuum pressure was applied and the entirety was cooked. The result was a core that was pre-formed to exactly the hull shape leaving no gaps. We also saw zero spring-back, which
meant our plan to build the hull in one shot was possible. What we mean by one shot is that the outer skin/core/inner skin are assembled in the mould and all cured together in one cycle. This method of construction is preferable
where pre-release of the hull from the mould is likely to be encountered, which is usually caused by laminate imbalances, shrinkage and mould expansion/contraction in the
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