Boating NZ : FREE TO READ April 2014
66 Boating New Zealand April 2014 carvel planking, however as glue can ooze out past the splines as they are installed, it’s safer to install the splines from the bottom up to prevent excess glue entering the grooves before the work is ready for it. The final job before sheathing is longboard fairing and sanding; obviously, the quality of the overall finish depends on the effort put in with the longboarding. SHEATHING It’s highly recommended that a technical advisor for the company which supplies the resin/fibreglass inspects the boat prior to sheathing to give specific recommendations. This can help to avoid flaws in the final result and ensure a smoother application process throughout. Ideally the actual sheathing should be completed in a day. If that’s not possible, then over two consecutive days. This will require careful preparation: a clean, organised worksite; sufficient materials on hand – ie, epoxy, pumps, trays, rollers, brushes, fibreglass, scissors, thinners, masks, gloves; suitable weather and sufficient people. Sheathing a 12m classic will need a team of at least four. While the mechanics of sheathing a boat in epoxy/glass are well covered in literature available from epoxy resin suppliers, there are some issues that apply specifically when sheathing classics. Fibreglass cloth lay-ups are typically heavier than the single layer of boat cloth on new work. This increases the structural strength to combat any potential plank movement. Grant Beck of Adhesive Technologies, the licensed manufacturer of WEST Epoxy, suggests a minimum lay-up for a 12m classic would be 600g double-bias (DB) cloth, covered by 300g boat cloth. A heavier lay-up would be three layers: one each of 600g DB, 430g DB and 300g boat cloth. The use of peel ply is recommended when sheathing. It’s a light fabric that’s applied after the final resin coat. It protects the lay-up from contaminates, absorbs any excess resin and, after removal, leaves a nicely textured surface ready for light sanding and the next stage. Gravity is another issue. New boats are normally sheathed upside-down, whereas classics are sheathed upright. On the underwater sections especially, gravity will be trying to pull the fibreglass cloth away from the hull, which isn’t good for maximum adhesion. This is why multiple layers of fibreglass are recommended – a single layer of fibreglass is too heavy to resist gravity. Olson counters gravity by pre-coating the hull with resin about four rolls of fibreglass cloth wide. He leaves this resin to become tacky enough to hold the fibreglass cloth, which is rolled out one width at a time from gunwale to keel. This first layer of fibreglass is allowed to go tacky before the next layer is added, and so forth. The splining process 1. Normal carved plank seam filled with cotton and putty. 1 2 3 4 2. Plank seam after grooving is completed, left to dry. 3. Splining done with spline left proud until glue has cleared. 4. Finished spline after fairing. Waimiga after sheathing, floating 50mm higher with drier, lighter planking. Ngaio being longboarded after sheathing in epoxy/glass. REGULAR_PB_fibreglass PTII_April14.indd 66 18/03/2014 5:27:29 p.m.
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