Foil Setup

After listening to the latest mothcast I decided to check my main foil angle of attack. I made a template of the foil section and drew the chord line and lines at 1.5, 2.5, and 3.5 degrees. It slips over the tip of the foil. I added some thickness to the trailing edge and did a really quick and dirty job of fairing the thickness into the flap. I've got it in pdf and dwg formats, so if anyone wants it I'm happy to email it to them. It plots on a letter sized sheet. I used a laser level to get the boat level and then shot it on the template. Wow, my foil was at not much more than 1/4 of a degree! That explains a little why I had to hike off the back of the wingbar and was sailing around in full flap down mode. I guess I was a little less than accurate in drilling the hole for my main foil and/or set it up at the wrong angle. I thought I was doing the right thing by putting the daggerboard at 7 degrees of forward rake, but apparently not. Needless to say, the boat sails a lot better now.

I didn't realize people would be so interested in the photo of Karl's boat. My attitude is that the more people that see your stuff the better, and I hope that everyone takes another look at the bowsprit concept. It's definitely on my list of stuff to do once I figure out how to keep the boat upright. The funny thing is that the bowsprit is possibly the least radical part of Karl's setup.

Flashes of Brilliance

A lot has happened since my last post.

I competed in my first moth regatta. It went about as well as I expected. Had some good moments, including rounding the top mark in second with a pretty big gap between me and the guys behind me (that ended when my vang blew up on the downwind.), and also had plenty of mechanical issues. The second gantry is holding up well so far, it does everything it's supposed to and hasn't self destructed yet. Richard won, and Paul came in a close second after driving all the way down from Santa Cruz. Karl's boat showed some impressive speed at times as well, I'm excited to see the further development of the tilt-a-whirl. Here's some pictures:

In other news, Chinchillazilla#2 was launched. Bobby worked almost non stop to get it done after getting back from South Africa. There wasn't much wind for the launch, but it floated, which is good. Richard took some pics:

The boat looks great!

Next up is the Turkey Day regatta in a couple of weekends. Should be great and we're hoping to get some of the mothies from San Diego to come up.

Gantry #2

So here's my second attempt at a gantry. Its got a different control mechanism too. I told myself when I launched the boat that I wouldn't change anything till I figured out how to sail it, but breaking my first gantry accelerated my development program a bit. The new one has held together through two days of sailing in 0-5 kts so still haven't been able to really put it to the test. The adjustment mechanism seems to work. The biggest problem is now that I can adjust rudder angle easily, it's easy to put it in the wrong place.

There's a million things I would do differently for the next one, and might get the chance to do soon, as Karl's new rudder is coming along and he's thinking about a new gantry to go with it.

It weighs about 725g with the adjustment mechanism which is about 200g heavier than the last one. I think I could get about 150g out of it easily for the next one. What's a good weight for a gantry?

Gantry #1 RIP

I've got five days on the water now and had my first major breakage. While blasting downwind my gantry decided it wanted to turn left while I was turning right. What actually failed was one of the attachments to the hull. This was two weekends ago and I've spent the last week and a half designing and building a new one. When I built the first one there was almost no engineering involved, so I decided I'd put in a little more time in the design department. I definitely underestimated the side loads created when foiling at high speed and how easy it is to load up the gantry with less than smooth steering (which right now is pretty much the only kind of steering going on).

The question is: how much load is there really? If you assume a Cl and speed for the rudder, you get a load that if applied to you and the boat, would quickly flip the boat/vaporize the rudder/accelerate you sideways quickly enough to make you black out. This doesn't seem to be a realistic load case. I think a more reasonable load case is applying the full righting moment and resultant sideforce to the rudder with a safety factor. Any more than this in theory would capsize you.

A second thought: how many gantries actually fail in buckling versus a failure of the attachment points/joints? It seems like it's pretty easy to design a tube for good buckling strength, but designing an attachment or joint that can handle all the multitudinous load cases is the tough part. Given my gantry failure data set currently has one point in it, I don't have much to go on. Anyone have any thoughts?

Congrats to Karl on getting married! I hope this doesn't affect his mothing time too much.

I'll post some pics of the new gantry as soon as its on the boat.

First Sail

Finally!

Now that the boat is in the water I thought I'd start blogging. I've got some pictures of the construction which I'll post over the next month or so. My favorite moth blogs have pictures of boat setups and technical information, so I'll try to keep the content along those lines.

First, proof that the boat does in fact float:

This project started out last fall when one of my coworkers, Bobby, and I decided we wanted to build some boats. A-cats were great, but a little beyond our budget and space availability. Neither of us had built composite boats or sailed moths at all so we tried to keep the design as conservative as we could. To make a long story short, after lots of starts and stops, I finally launched my boat yesterday. Bobby's is going to have to wait a bit as he's headed to Cape Town for a few weeks on Thursday. The boat seems strong enough in the right places and actually foiled on the first tack away from the launch ramp after more than a few capsizes getting into the boat for the first time. The basic setup is:

-Home build hull

-Fastacraft main foil (old version)

-Fastacraft wand and control cable (Karl's stuff from his boat's former life as a garden variety prowler)

-Homebuild rudder (I think we went for about 110 in^2, I'll have to check)

-C-Tech rig

-North V6 sail.

Here I am heading out:

Had a great first sail in puffy and light stuff and was mostly focused on keeping the boat upright, but had a few low altitude flights. The day ended when one of the nicropresses on one of the shrouds I made in a hurry at West Marine gave out and the rig came down. Wasn't a big deal as I was in a small bay and there was no damage. The boat itself was great though, not a drop of water it it!

I owe a huge thanks to Karl for all of his help through out the project, he put up with what must have seemed like constant phone calls and requests to borrow things, as well as putting a lot of work in at the shop.

Lastly, here's a really short video of me crashing. This one was actually on purpose because I thought I saw the harbor patrol coming (I swear).

Test Post

Lets give this a try!