Stripbuilding - in reverse

Back a few years ago, I tried an F-48 multihull build using the “female” template molds of the design. I attempted to layup the hull halves using thin foam strips instead of wood/balsa layup so I was looking at the inside of the hull instead of the normal strip-build process where a “male” template is covered on the outside by strips.

Using a male template, (inside shape of hull) one normally attaches the strips of the hull to the outside of the template and then fills/sands/fairs the external surface.

I tried using the foam strips to layup inside the female template (outside shape of hull) so that the strips attach to the inside (female) version of the templates.

I found I had difficulty holding the strips in place and any glue seepage was terribly hard to sand as the foam around the glue-drip was so much harder. Also, gluing the foam strip to the template caused the foam to have small holes/dents once I tried to remove the strips from the template shape. Thus, since I couldn’t hold the strips in place as I continued to build, I gave up on the idea, even though it was used for a large powerboat build. (real life-size)

Today, while looking for some possible catamaran plans to build a 10-12 foot cat for my grandson to actually sit on and sail, I ran across a web post of a build log done by a guy in Finland (as I recall) It drew my interest as he showed building the hulls in two halves just like I tried to do. Investigating, I found he solved my problem of holding the foam strips against the templates and his process should work regardless of male or female templates.

Basically for each template, instead of covering the shape with tape to keep the strips from sticking, he used the thin, foam, double-sided tape which held the foam strips in contact with the template. Between templates he simply added masking tape to help keep the strips together to each other, and from drooping between the station templates. As noted, he built INSIDE the template - not outside, and when done, simply gave the foam a coat of thick (honey consistency) epoxy and a layer of glass. The foam didn’t stick to the double-sided tape, and so the entire half hull was easily removed. Turning the hull over, with the exterior facing up, he simply filled the cracks between the strips with a bit thicker epoxy, sanding any high spots first, and then added a layer of glass - so when done, the hull is foam strips sandwiched between a layer of interior and exterior glass. Because the hull was to be painted, there was no need for critical strip matching - allowing the thickened epoxy to fill any gaps.

I thought there might be someone willing to try this method of using tape to hold strips in place on a “male” template so decided to post the idea/process here in case anyone wanted to try. As noted, his boat was a Formula 12 (12 feet long) and so using tape might be easier with thicker templates.

Anyhow, just an idea that is being used to quickly build foam core strip hulls, and according to the builder - weight was very competitive with a wooden ply hull of a slightly different design.

If anyone tries this, please post on how well it works. If I proceed with grandson’s boat, I’ll let you know what works and what didn’t. Or - may try this on a large r/c boat in the 1/10 or 1/20 scale size.