How Do You Build It?

So how do you build a moth? Well, there are lots of ways, some easier than others. My goal was to use a construction technique that would be simple and cheap and yet relatively tough and light. I really like Phil S’s technique using tortured marine plywood. But my design not only called for torturing plywood, but also creasing it. So how do you fold plywood? I wasn’t sure, but I had some ideas. These ideas needed to be tested before I finalized my design. I got several 2’x2’ sheets of 3mm Okoume marine plywood and began to test folding techniques. After just a few tries I found that plywood can be folded pretty easily. Here’s what you need to do, first you need to groove the plywood where you want it to fold and remove enough material from the back side of the fold so that it does not bind upon folding (about 60% of the 3mm ply for a 90deg bend) Then you wet the wood and heat it with a hot iron. After you do this you will find that it folds pretty easily. Let dry and then glue on place. Done. First obstacle down.

After working on the folding technique I went ahead and build a 1:8 scale model of the boat with the 3mm ply. Turned out pretty good I think. I was also able to use this model to estimate the weight of the basic hull (no internal frames or deck). 13lb. Not bad. Granted I still need to add a lot of stuff and the final hull weight will probably be +2x that weight, but it’s an ok start.

While plywood construction is pretty effective for a job like this, it will not be as light as a fully vacuum bagged carbon foam construction. Also, the raw plywood is not great on durability so I intend to give it a single layer carbon skin over the hull on the outside only. This will present some construction challenges and add some weight, but it’s probably worth it to make a boat that will last.

Next Time – Parts and Pieces

The Design

The hull on the modern Moth does very little. Unless the wind is low, the hull is totally out of the water. So other than aerodynamics and weight, the hull has very little impact on sailing. For this reason, you don’t need to have a highly specialized and evolved hull design. There are some important design considerations and you do spend some time with the hull in the water, but for the most part you can have whatever shape hull you want.

My hull design was based off of Phil S’s plywood moth design. The overall structure of the boat was reduced considerably from Phil’s designs to more closely resemble the newest generation of boats. I also wanted to put some pretty hard chines on the hull. Although a round hull is faster going through the water, a flatter hull with hard chines will plane faster and theoretically fly sooner.

Here are some pictures of the iterations of hulls shapes I created using cardboard. I tweaked each hull generation slightly until I got a hull that looked how I wanted it. I think the final result looks pretty good. After I completed my final design I discovered Doug Culnane’s moth Blog. Doug has been building moths for years and seems to know what he’s doing. His blog was nice enough to provide measurements at key points all over his newest boat. I started looking at these measurements and checking how close I was with my design. The verdict: close, really close, scary close, I-promise-I-did-not-copy-your-boat-design-Doug close. The reality is that Doug and I chose to do somewhat of a similar construction technique and that technique really lends itself to this boat shape. At least that’s the story I’m going with.

The only real difference the Mothball One will have from other modern designs will be the knuckle bow. This is a modification that I came up with which should have some good effects on sailing. The idea came from the latest generation of America’s Cup boats. If this design is used on the ultimate seahugger boats, then it should hopefully have some good effects on moth sailing when in seahugging mode, in theory. Also, it should improve the touchdown handling of the boat. The knuckle bow should impact the water all at once which will hopefully reduce the water entry speed and lessen the nose dive tendency... in theory.

Next Time – Construction Technique.

So Why a Moth?

Cuz they’re cool, that’s why!

But I suppose there is a bit more too it than that. I have never sailed a moth. But I have been sailing since forever and did a lot of windsurfing when I was younger. I purchased my first real boat in 1999, a penultimate International 14. It took me years to really get a handle on how to sail a high performance boat. I sailed the I14 at the Worlds in Long Beach in 2006 and had a blast. We did fairly well considering we had the oldest boat in the fleet and were not up the current rules standards.

In 2007 we had a little baby girl Megan. She is probably the cutest little girl ever, but it became really clear that Megan was not going to be sailing an I14 for a very long time. We also have a SanJuan 21 for a family/class racing boat, so the I14 sailing became pretty questionable and the concept of having a small one person super-high performance boat became really appealing. The Moth was the natural fit.

So why build a moth. Well, several reasons. First, cuz it’s going to be way cheaper than buying one. Secondly, cuz I can. I’ve done a lot of work with epoxy and carbon over the years and my background as a civil engineer gives me a pretty good handle on the structural part. Also, I have collected several sets of random carbon tubes which are the exact right sizes to build the racks, for a savings of $1000 or more. Building a boat from nothing is pretty appealing to me. It should be a great learning experience and is great for your sailing cred.

Next time, the design.

Step One

In compliance with Section 12.4a of IMCA rules, this is the official blog of Mothball One, the Montana Moth Project, Bobzilla vs. Mothra. This blog will be the full account of the construction of the International Foiling Moth, Mothball One.

Here are some links of Interest.

The US Moth Website

Spaceball One!

Stay Tuned for Actual Content!