A series of pictures showing how-to build a fiberglass hull. The hull pictured is a 1/35th scale Huckins PT Boat, I made this hull for those who may have the Italeri Elco PT Boat kit and want to expand their collection. The Italeri PT-109 kit will provide the vast majority of the fittings and armaments although some scratch-building will be necessary. The first step to building the hull (once you have sized and printed your drawing to the desired scale) is to decide what method you will use to build the plug, this will determine how much you allow for keel and skin thickness when cutting the frames. I have built this plug using 4mm fiberboard meaning I need to allow 2mm off the inside edges of the frames for the keel thickness. The outside edges of the frames will extend to the outer surface of the skin so no further adjustment is needed. Cut the deck and backbone/keel leaving a gap aft, this is so you can fit a Plexiglas transom later on, as you will never get a perfect transom otherwise, and assemble as shown in the first picture, ensure the frames are positioned at right angles to the keel and bond using a glue gun. Use stiff cardboard to approximately form the skin of the hull. Ensure the cardboard does not quite extend to the surface as this will be a problem later when you sand it. Once you are happy with this assembly (check it very carefully for twist) paint it with polyester resin and allow it to dry hard. Use polyester filler to build up layers level with the frame edges, at first using the frames themselves to run the spreader over. Once you have the basic shape, build up more filler and sand it back with a 50g paper, bit by bit, being careful never to sand the frame edges themselves otherwise you will lose the correct form of the hull. Use a former as your hand is not boat shaped. Don't worry if after you have finished sanding a couple of frame edges are slightly covered, this is normal and is better than a hull which not fair. sand off the scratches with 120g paper. Glue some blocks to the deck to allow a gap under the plug when inverted. Paint the plug again with resin, let it dry then sand it smooth with 240g wet and dry sandpaper. Wax it up using a mold release wax, let this dry completely and buff it to shine. Repeat this twice more. paint it with gelcoat, a nice generous neat coat. Let that dry (it will squeak when you run your finger against it) and paint it again, this time mix resin into the gelcoat at 10-15% or so. Once that is dry, take your resin, mix in a little gelcoat as this will help make the mold less brittle (and it is less smelly this way when it is going off), and a powder thickening agent. The shape of the hull will determine how much powder to add, you will need to apply a thicker layer of resin mix to areas with hard edges i.e. the chine edges, the stem, the keel etc. Paint a less thick mixture (by adding resin to your mix) to the rest of the plug. Cover the whole thing with strips of chop strand mat, I use 330g which works well for me. Nice big overlaps will give added strength and help prevent distortion. With your latex-gloved hands, smooth the mat down onto the plug, and work it in gently so the resin begins to soak through the mat. Pour a little extra resin into the remaining mix and use this to wet out thoroughly, use a washer roller to help if you have one, or stipple it carefully with your brush, cavities are your enemy and you must eliminate all of them completely. A tip is to use at 2 pots of resin mix, containing different thicknesses, and a third pot neat. The bottom half of a Tetra-Brik container make ideal mixing pots. For goodness sake do not forget to mix in the catalyst before application. Let the mold dry completely. Cut off the overhanging fiberglass and separate the mold from the plug, this should not be difficult if you waxed it all properly. If you need to insert a tool to help you, use a plastic spreader or soft wooden mixing sticks, something which cannot scratch the inside surface. Once you have released the mold, check it for any irregularities. If you need to do any filling do it from the outside, i.e. gently grind the outside surface until the offending area is exposed, tape over the inside and fill against the tape. This will massively reduce sanding later and spoiling your nice inside finish. The wax residue left in the mold from the plug means you need to only do 2 new coats of wax in the mold prior to laying up you first hull (subsequent hulls will need only one new coat of wax in the mold). All the same tips apply to building the hull as to building the mold, careful to build in as much lightness as possible where strength is not vital, and extra strength where it is needed i.e. the transom, the areas of the hull where the sterngear will penetrate, the gunwhale edges, use overlaps, figure out how best to cut the mat to secure the transom firmly to the hull and form the stem without doubling and tripling the mat thickness, also be sure to paint resin from the outside where the hull extends slightly from the mold, this helps prevent the deck edge from chipping. Small chips can easily be repaired later by placing a spot of superglue in the cavity and lightly dry sanding the area around it, the dust will stick to the glue and create an invisible repair. When it's dry cut off the excess from the edge, careful not to cut anything from the mold. Once the joint is exposed all the way around the edge, work the hull from the mold by gently pulling the 2 sides apart. If all has gone according to plan the hull will separate from the mold with no further persuasion. Give the hull a good wipe with acetone inside and out to remove all the wax residue. Cut the deck using the drawings as a guide, do not the hull as a template as it will have pulled in slightly, the correct deck shape will push it out into the proper shape. Store the mold with the plug inside it to prevent distortion. Good luck!
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Topic: Build a plug, mould and hull. (Read 3719 times)