When Rob was asked to visit the Marshall Islands in September to teach the locals how to build and sail the mini cargo ferry, he thought it would be smart to build a prototype to ensure he didn’t make a fool of himself and to test some ideas to make building them quicker and easier. One of the critical things with this boat is longevity and ease of build by unskilled workers. Ensuring everything had 3 coats of epoxy was critical. The best way to do this is to glass all components, then peel ply or baking paper the surface. This policy was carried through to the stringers, which were triangular in shape and included in the glassing. Cutting them was right on the limits of the $100 table saw and undressed timber stock, but it managed. Triangular fillets are hard to clamp and time was short, so rather than adapt the clamps and limit the amount of joining per day, screws were used. Incorrectly prepared screws and poorly filled screw holes are by far the most common starting point of rot in sheathed ply boats, both of which take up an extraordinary amount of time. In the Marshall’s boats, they will not be used.
The ply is interesting. The veneers are medium/poor quality (Grade B and C, D is as bad as it gets) which are plenty strong, but have knots and flaws. These are covered with very thin (less than a millimetre) veneers on each side and it looks like high quality. It glues and glasses well, is stable (for plywood) and did not move when it got rained on and humidity skyrocketed. $Aus50 per 6mm sheet, including cutting it to size. The sheets of ply were precut into half width pieces for the bottom, deck and cockpit and 2/3 sheets for the sides. The bow curve was cut using a batten, then transferred to the other pieces, no measuring required. The full length pieces were then butt joined and a layer of glass applied on both sides to the join. The 1/3 pieces were joined lengthwise to make 2/3 sheets. The stringers were added and everything was glassed on one side.
The bulkheads were cut to length from the remaining part sheets, stringers and glass added and glued to the hull bottom. Because everything is straight, alignment was simple. Eyeball and string line were fine.
The sides were bent and glued into place and the cockpit glued in. All straightforward. The bows were joined, screw holes filled, deliberately exposed ply edges filled with glue and the exterior glassed, with extra layers on the joins, bows, chines and gunwhales. It was then peel plied to protect it from the sun until it gets painted and to give a key for the paint.
The completed hull weighs 110 kgs, took 53 hours. The next one will be quicker. Building a 7m hull in a 6m garage on rainy days is slow. As is insufficient floor space to glass all the sheets at the same time. There was a small screw up with panel alignment (easily fixed), and a problem with using the wrong screws rather than going to the shop and buying the right ones. This necessitated using a soldering iron to soften the epoxy so 30 of them could be removed. Drudgery. Especially when Rule #1 was: No screws! False economy all round, will not happen again.
The whole job was a bit of a blast from the past. Lots of fun, apart from the sticky/dusty and a great reminder of how much quicker, cheaper, simpler and cleaner Intelligent Infusion is. I will be packing a small vac pump and materials required for a demo along with my kite gear and sun hat in September.
The next step is to build the beams and the second hull. We have also found some easy use epoxy. 2:1 by volume, long open time for high temperatures (40 minutes at 35C), good solar resistance, different coloured resin/hardener which combine to make a third colour and cheap at $Aus11/kg. Plus there is a video to film, showing beginners how to use epoxy in reliable and time efficient ways.