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Boating NZ : FREE TO READ March 2014
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Carvel planked decks will need their seams splined; we will look at this more closely next month. Alternatively, they can be sheathed with plywood. If laid, teak-over- plywood decks are to be sheathed, the teak will need to be removed and replaced with plywood. Because of its inherent strength, the plywood can be a little less thick, say 75%, of the original teak. Most classic boat decks and cabins have awkward obstructions such as toe rails, hatch runners, hatch upstands and handrails. Their tricky right angle corners can be difficult to sheath around during the main glassing job. It’s often easer to remove these obstructions so the main deck/ cabin can be sheathed in full-width rolls of glass. Toe rails and hatch runners, for example, are re-installed and glassed separately. DRYING If you look at timber under a microscope, you’ll see it is composed of longitudinal hollow cells many times longer than their diameters. Timber cells in the underwater sections will retain water, hindering the epoxy resin from migrating into the timber cells as it should. This will weaken the critical timber to epoxy/ glass interface. Drying the underwater sections of a classic is a process rather than an event, and will take weeks. If the hull is to be splined, the spline grooves can be cut early in the process as this assists drying. The boat should be dried naturally and slowly, otherwise there’s a major risk of the planks warping, checking and cracking. While de-humidifiers, fans and heaters may seem an obvious tool, their use is not recommended as they can dry the planking too quickly. Slow and steady is the key, and progress should be monitored closely throughout. As the hull dries, it should be regularly washed in fresh water, say two to three times per week, which slows the drying and helps remove the salt contamination; next section. All timbers must be dried to the local ambient moisture content, which in Auckland is around 12% to 16%. This is easily measured with a moisture meter with a prod so that measurements are taken from well THE CASE FOR • Improves the boat’s longevity, especially if the boat is raced and sailed hard • Keeps the boat’s timber dry, which retains the timber's strength • Keeps the fastenings dry, which slows corrosion and helps protect them galvanically • Creates a stiffer, stronger surface, with better protection against bumps and knocks • Better protection against fresh water ingress in the decks and cabin structure • Stiffens the boat’s structural integrity, especially when combined with splining • Dry bilges • Less overall weight due to not having waterlogged timbers underwater • Eliminates caulking and leaky seams underwater, eliminates cracked paint seams in the topsides • Stabilises the external timber surface to allow the use of two- pack paints, which are inherently more resilient and longer lasting than single-pack paints • Allows the use of dark-coloured paint, with precautions • Exterior maintenance requirements are considerably eased THE CASE AGAINST • Classic timber boats are structurally flexible; unless they are strengthened, the relatively rigid epoxy/glass sheathing can crack on the seams, allowing fresh water into the structure where it gets trapped and creates decay • Sheathing timbers that have been soaked in seawater for decades requires specialist drying and salt removal • Due to gravity, it’s physically difficult to epoxy/fibreglass sheathe an upright boat, plus it’s difficult to sheath the likes of hatch upstands, toe rails and window surrounds • A properly done epoxy/glass sheathing job on a classic boat will cost significant time, money and energy, and probably over-capitalise the boat • A poorly done sheathing job will create far more problems than it solves • Sheathing can conceal rot and other issues and complicates future repairs • Painting sheathed hulls in dark paints can cause delamination of the sheathing due to differing thermal rates of expansion • A classic boat’s originality status is compromised when sheathed in epoxy/glass The sheathing classic timber boat debate “Meths helps to dry the hull and to bring the salt to the surface” ABOVE: Waimiga after sheathing and painting; note the excellent finish. TOP LEFT:Ngaio at relaunching after sheathing and painting; an excellent finish for a 92-year-old boat. 78 Boating New Zealand March 2014 Feature_Fibre glassing_March14.indd 78 18/02/2014 2:16:44 p.m.
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