US1M magic build

Okay, I have narrowed down my list of possible hulls, and found one I liked that wasn’t on the list to begin with. Isnt that something. Anyways, I have a good start on the male mold, the foam is cut out and glued together, next will be sanding to shape and glassing. After that, I’m gonna pop a hull off of it, as a male mold. The usual wax and pva. My question is, what should I use to laminate the hull? I have .75 oz, 1.5 oz, and 6 oz cloth. I was thinking a layer of .75, then the 6, then another layer of .75. Would this be to thin? To much? I could go with 4 layers of 1.5, or even less. I’ve never done this much, I did a rg65 hull once with 2 layers of 6 oz and got fussed at by some members of this forum! It was all done in good cheer, but I don’t want to make the same stupid mistake again, I need a high performance hull, not another clunker (I build those out of wood!)

I think your ‘confusion’ for want of a more appropriate word is that the majority of the experienced builders on this forum tend to quote their cloth weights in grams/sq metre. As far as I’m aware US notation tends to be oz/sq yard. To get an approximation simply multiply the oz number by 33.977 (or 34 to keep things simple).

Thus, your 0.75 oz cloth equates to 25.48 g/sq metre (25 grams/sq metre)
1.5 oz cloth equates to 50.97 g/sq metre (50 grams/sq metre)
6.0 oz cloth equates to 203.86 g/sq metre (200 grams/sq metre)

In Claudio’s 123 build he used 3 layers of 105 gsm, giving a total cloth weight of 315 gsm & a theoretical all up laminate weight of 630 gsm including the epoxy. Bearing this in mind I’d of thought 1 layer of your 1.5 oz followed by 1 of 6 oz and a final layer of your 1.5 oz, giving a similar overall laminate weight as the 123. In my limited experience the heavier cloths tend to be easier to use/handle than the lighter one’s. From a practical perspective I’d prefer to use the same sort of cloth weights as claudio but seeing as you already have other weights ‘in stock’ I’d be inclined to go with what you’ve already got.

Good luck with the build & keep us posted with your progress.


Thank you twister. I’m gonna start posting pictures once I get the plug faired and glassed, right now I’m waiting for some epoxy to cure, then more shaping of the foam. At least it’s easy to work with!

Well, I’m almost done carving out the male mold. Once that is finished, I’ll snap a few pictures. Another question, is in necessary to fiberglass the foam mold, or can I just wrap it with packing tape?

packing tape should work fine

I’d imagine the only time it’d be necessary to glass the plug would be if it needed a lot of filling and fairing - if you’ve managed to achieve a smooth & fair shape then as Hew stated, just packing tape is sufficient. At least going down that route you won’t need to bother about mold release waxes or other proprietary release chemicals.


Well, I pulled a hull. It turned out pretty good, learned some things for the next build. I’m gonna put in some clamps and a few formers and whatnot, I’ll post pics as soon as I can figure out how to get them off my camera!

So, frustration set in, and the project was scrapped. I didn’t find out until I tried setting the formers for keel box, but I had a pretty bad asymetrical section. I’m gonna start work on the project again, gonna pull the packing tape off, sand the plug fair, and try again. Or I might just scrap that plug, and start over again. Pictures coming!

Using some templates on the plug, it doesn’t look like it’s gonna be salvageable. It’s a shame, but it is what it is. So now, I am back to square one. I think this time i’ll go a little slower.

If you have cross section profiles for your hull - translate them to paper. Do not leave any extra length to the templates - the hull shape should stop EXACTLY at the point of hull to deck dimension. Then spray glue and attach the paper to a piece of stiff aluminum gutter stock, or 1/8 thick (maximum) plywood. Cut out and mark each template. On the inside curve (of the hull shape) grind/sand a sharp edge on that portion of the template that reflects the curved shape of the hull at that point along the length of the hull. Make sure you keep the template perpendicular to the hull, and also perpendicular to the keel line and place the template on the top surface (bottom of the hull) and begin to lightly tap the template with a small hammer to force the template to cut into the foam with the sharp edge. As noted above, when the template touches the top of the table/worksurface it will have “cut” the hull shape into the foam. Use a coarse grit (60 or 80 grit) piece of sandpaper (very coarse) glued to a scrap of that 1/8 thick plywood about 1-2 inches wide and about 6 inches long, and begin to sand down the foam directly on top of the template “cut” until you can just see the bottom of the cut. Now move to the next template location and repeat the process. After you do this for each template location, you will have brought the foam down to “almost” it’s final size. Now, all that is needed is to use a wider sandpaper stick and remove the foam between each of the template locations. In doing this, you have first established the shape of the hull at the template locations to within a close dimension, and then you basically “connect the dots” (cut lines of template) to obtain a smooth transition for the entire hull length from one template cut to the next. Once you have the shape and are down so the template cut lines are barely visible, switch to some 150 grit paper to give a reasonably smooth finish and then apply the plastic packaging tape over the hull. Lay the tape on a slight diagonal with the keel line which will help it lay flat in both directions, and be sure to overlap the tape slightly to prevent any glass from sticking to your male hull shape.

I usually use the aluminum for seamless gutters (you can ask local companies for a chunk from their end roll that is too short for a full gutter profile) as it can be kept sharper than the wood. Also it is thinner so it is stiff enough to press down to cut into foam, but the thicker the template, the harder to get a nice sharp cut. If you find the aluminum to difficult to press into the foam, try sharpening the shape more.

Good luck Dick

I guess, in a way it is like cutting Christmas cookies … sort of.