Finally, here is the long awaited part 2 of how to home build a moth. This one covers how to construct your own hydrofoils

Home Building a Carbon Moth Part 2 – Foils

The repair of my T is well underway, although it won’t be ready this weekend as I hoped, as last weekend was spend building a nice new work bench in the garage.

With the bench done, it was time to get beck to the foil repair, and building a new T. The new T adopts a completely different approach to the last one. The T’s are cut out of a large, very thick slab of carbon, instead of being two L’s which form the T. You can see the difference in the two photos, with the new T’s sitting in place, prior to trimming and gluing in.

As you can see they are very thick this time around and are engineered to be significantly stronger, through different fibre orientation than the old one. The main reason they can be so much thicker is that these T’s will replace the outer skins on the vertical, and not sit inside them, just like my nationals quick fix.

It is also interesting to see how much the foil has “aged” since it was originally glued together … I think that a coat of paint and some polishing is in order.

The two black bits of my foil were glued together yesterday and I now have one, single black bit to take its place.

Next job on the to-do list: tagging the joins with carbon, then it’s fitting time !

That makes it time for the boat to come home and be pulled apart again, oh joy.

The other challenge that I am having is my foil somehow ended up being 30mm shorter than the last one. As a result my push-rod is now 30mm too long, so I am going to have to cut it and weld a shackle on the end instead. The issue is that trying to find someone who can weld stainless it whilst working 9-5 Monday to Friday is a complete pain.

Even though this is the fifth foil that I have built, this is the first that I have used the build, cut, insert method for making a flap. So step one was to get out the trusty Dremel and the hacksaw and cut my foil in two pieces … (I was crying on the inside when I started cutting). Once I could see inside the foil this is where I changed my mind. I was going to make a piano style hinge out of carbon tubes, but I decided to use my tried and true method of using gasket rubber.

This stuff works like a charm. It is flexible and durable, and has been in good service in my current old rudder for 3 years now, and my current centreboard for 2 years. Should I decide to change my mind in the future post-nationals, I decided to use “Bladerider Flap Adhesive®”, (aka Sikaflex) to bond it in place.

My vertical foil has now been fully bonded together, and is ready for trimming to shape (hence the holes you can see in the photos). My target weight for the vertical has been achieved with it coming in at 1.524 kg, before trimming.

Assuming the material that is yet be removed will equal the weight of the glue and carbon that is to be added when bonding the horizontal to the vertical, I have achieved my 2.5 kg target weight, and I think that I have increased my foil stiffness by 4-5 times my current one.

The difference between this foil and my current one should be the moth equivalent of bolting on twin turbos.