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Making a Fibreglass Hull

These notes cover much of the process used to build the hull of a small model tug (18 inches LOA). The hull is formed from two layers of fibreglass. I have built several model boats up to four feet long, using this technique (though with more layers). The model airplane dope I used on the tissue paper is called “Eze Dope”, it’s non-toxic and although I bought it some years ago, I think it’s still available on Amazon. It keeps for ages. After its applied, you can use an acrylic spay before applying the fibreglass, that helps to minimize sag if you have a large spacing between frames. For small spacing, it’s not needed. If you can’t get the dope, you can use a flour and water paste to do the same thing (when I started building model planes, things like model dope were hard to get and flour and water was all that was available). I have used polyester resin because I ran out of epoxy resin. I much prefer working with the epoxy but because of the minimum quantities that are required for purchase, “poly” is cheaper for small amounts ……. it’s smelly stuff and can set too quickly if you user too much hardener. It also seems to be more temperature/humidity sensitive than epoxy. The tissue paper is just ordinary wrapping stuff (model airpane tissue is not needed).

I had to use balsa stringers because that was all I had, and basswood was not available at the right size. Balsa doesn’t steam-bend well so I had to crack-bend some of the stringers and then fair after the first layer of glass. Fortunately, the only piece of basswood that I had was good for the keel.

This is the first paper cover AFTER dope was applied. I put a second layer of tissue paper over the first (after doping), where it was torn or looked too “saggy”. Minor wrinkles don’t really matter. Nor do small air pockets between the layers. When the resin is applied over the first layer of fibreglass, it should also penetrate into the tissue paper, so that the entire cover bonds together.

I did have a little “Bondo” left from previous auto repairs and I used it to fair the undersurface of the fantail transom after I completed the papering But before glassing. The transom is made of layered balsa and the stringers are inset. Unfortunately, I had to complete the prop and rudder assemblies before I covered the frame and getting a true form finish was very difficult because the limited working space.

This shows the skin after first glassing, fairing with plastic wood filler, second glassing and then sanding to a smooth surface.

An extra coat of resin was then applied all over and lightly sanded to be ready to glue-on the cutwater and bilge keels, and then primer paint. Bulwarks and rub-rail have been added at deck level.

Hope this is of interest, Peter

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