JAnimis

For the frames being rigid is a good thing. We're going to have to see if the tube will bend enough for stringers. On a skinny 20' boat it might bend enough. If we run into stability issues, we can add sponsons or outriggers (we actually made some for the Matilda, but after the first sea test we realized we didn't need them). Hopefully they'll only be needed as trainging wheels while the pilots are learning to handle the boat.

I'll keep you updated. I'm sure I'll have some questions for the forum as we proceed. We do have a new hull design this year. The Matilda is great, but it turns out to be way more stable than we need. Since we have an electric motor, the pilot doesn't have to move around much so we are going very narrow - more like a racing skull or surfski. Though we are going with a wide flat stern because we think we might get enough speed to plane a bit (if our calculations are right, we are just short of having enough power for a hydrofoil).

Last year I helped a Middle School club build a SOF boat (Matilda) for the Northern California Solar Regatta. They won "Best Design" and did very well in the races. Their performance, an the performance of the boat convinced me that SOF is the way to go for this race, so we are building a new one this year. The method of construction allows11-13 yr. olds to build pretty much any hull shape they want in a few months is amazing. We are going to try to take it to extremes this year with carbon sandwich panel frames and carbon tube stringers to see if we can get our 20' boat down to around 10 lbs (and we have a few other ideas from the Skunk Works). We've launched an Indiegogo campaign to try to raise funds for materials. If you would like to help, spread the word. Thanks. https://www.indiegogo.com/projects/ldv-dolphin-yacht-club-solar-boat/x/9123674 P.S. This is a great educational program for these kids or I wouldn't even consider posting something like this here. I hope I'm not out of line and please remove this post if I am.

Put a handle at the CG and let people pick it up - with one hand . I also agree that you should run a video, but I would show the toughness test.

What about a wooden grommet (I'm sure it has a different name on a boat, some kind of through fitting) to hold that bow loop and cover the hole? Fix it to the bow frame so it doesn't pull the fabric and glue the skin under the flange.

Here is a student produced video of the build and the race:

I am by no means an expert, but I can answer a few of your questions. If you can't get wood long enough for the stringers the you will need a scarf joint. Many here (myself included) use Titebond III for the scarf joints, gunwales, etc. You don't need epoxy for anything on these boats. Re. the polyester; as I understand it, Dacron, Ceconite, Poly-Fiber, etc. are just brand names for Dacron (DuPont trademark) fiber polyester fabric. The difference in the 'weight' of the fabric is the main factor in how 'tough' your skin will be. 11 oz. fabric will be more abrasion and puncture resistant than 3 oz. How and where you are boating will guide your decision about fabric weight.

There were a number of parents taking pictures and I think video. If I get copies, I can post them.

A lot of teams use trolling motors, but for these short distance races, high torque, low speed motors do much better. The 4 solar panels we are given are old decomissioned panels and at best put our 65W each. Motors like the Torqeedo and Electric Paddle are better suited to this race. We are in Sacramento but the race is held at Rancho Seco Park (SMUD has to use if for something ).

We were going to build our motor, but with less than a month to the race, a parent donated a Torqeedo 801 that he wasn't using. It was a mixed blessing. It would have been very difficult for us to build the motor and drivetrain we had planned, so the Torqeedo gave us a working motor. The problem is that it was too smart. It is a really nice, compact, and powerful motor, but it uses a complex computer controller that wasn't happy with the power we had available from the solar panels we were required to use. We had to ramp up our speed very slowly and carefully or the CPU would shut down the motor forcing a reboot that put us back to the slow ramp again. It was very easy to go over the tipping point. To his credit, our pilot only tripped it once, but those limitations killed our chances in the sprint and slalom races. If we use the Torqeedo next year, we hope to labotomize it and run our power straight to the motor.

Here it is on race day:

We also built a pair of amas thinking we might need extra stability. It turned out to be plenty stable without them so we raced without them.

Over past five months I have mentored a middle school team entry in the Northern California Solar Regatta (https://www.smud.org/en/about-smud/environment/renewable-energy/solar-regatta.htm). Our boat was based on the "Matilda" from Jeff's book. The boat performed well. It took second place in the endurance event and if we'd had a little more time to overcome a few issues with our motor, I think it would have been competive in the sprint and slalom as well. We also won "Best Boat Design" It was a great experience and we are looking forward to competing again next year. Here are some photos of the build: MDO frames, redwood stringers, keelson, and gunwales.

That looks better! I think I'll build this version. Thanks!

I may still be missing something (it wouldn't be the first time), but when I lay it out, this is what I get: And, looking at the numbers for the 1'6" frame, the last two points are only about a cm apart.