Back on the Water

The 2011 moth season has officially begun with a short but successful trip out onto the water. The boat worked great, the pilot not so much. But I didn't die or get hypothermia so I guess that's a good thing. Plus I got some pics! When I first headed out the wind was about perfect, probably 12kts and steady, good conditions for the first boating of the year. After getting things sorted a bit I headed out again but the wind was starting to come up more. By the time I turned around it was blowing pretty solid 20kts. I now know that I suck at reaching in 20kts. I had a really hard time getting the boat into a grove and I crashed to windward a lot. Thankfully Mothball 1 seems to have a good bow shape for going nose in. For as many times as she went in she never really felt like she was going to go down the mineshaft, even with the bow completely submerged to the mast.


I ended up in this position a lot. I could get up and going no problem and i was trying to keep the boat healed to windward, but I think I'm underestimating how much leverage you get with the boat when you are up on the foils. Clearly there was some wind out there though.


This is the only shot I got of actual foiling. Sorry for the blurry image, but I kind of like it. Its so blurry that its almost artsy. Anyway, the boat is clearly riding high, I could probably use more vang though. Man these sails need a lot of vang. A few rig mods to make now but I think Mothball 1 is going to have a very productive summer.

Bent Wand/Simple Ride Height Adjuster?

So I built my bent wand, it was quite simple. The main section is made of stiff carbon tube and bottom is a solid small diameter carbon round which is fairly flexible and fits inside the main tube. The lower section is set at about 50 deg off from main tube and has float made from a half section of larger carbon tube. When the boat is flying less than 10 cm above the water it will be controlled by the short main section and above that the 'bent' section will take control. Should work good I think. But I was playing with it and I came up with another cool feature than I could implement. Using the bent wand it would be easy to make a simple ride height adjuster. Simply attach a small diameter line the end of wand and then wrap it over the wand pivot and back to the cockpit. If you tighten this line the wand bends and effectively gets shorter. Simple. Will it work in the real world? I don't see why it wouldn't. Yes the tension on the line will have a small effect on wand pivot, but this effect could easily be compensated by adjusting the wand tensioner. No moving parts, nothing to get jammed, and very little added weight.

The Case for the Bent Wand

Snowed today. Five inches new on the ground. I'm not sure spring is coming this year. But I'm spending my time thinking about moth sailing anyway and I came up with an interesting idea. I'm not sure its a good idea, but it is an interesting thought problem related to moth sailing. So I need a new wand, no big deal, I have a ton of small carbon sections to build it out of. So what is the ideal wand shape? Most wands are straight, but do they need to be? What if your wand was bent? How would that effect how it senses the water? So here's the thought problem. Lets say you have a slightly longer wand that is bent 45deg about 2/3 of the way down. This would have the immediate effect of making you need to adjust your linkages, but thats pretty easy. When the wand is pointing down I don't think it would change much, except it would change the angle of the end float, which could be nice. But when the wand is up above 45 deg you could end up with some interesting effects. With the wand above 45 deg the knuckle of the wand would hit the water before the float does and would effectively make your wand much shorter when the boat is riding low. I made a diagram of this effect and as far as I can tell the net effect would be a change in gearing of the wand mechanism. When the boat is riding low the wand would sense the water at the knuckle and this would increase the rate of motion of the wand when riding low. When riding high beyond the knuckle the wand would function normally. So would this be a good thing or a bad thing? Effectively you'd get more flap motion when riding low and the same motion when riding high. Adjusting the angle and the location of the bend would create an infinite number of gearing options. You could also put in multiple bends to get different gearing at different ride heights. Has anyone tried this yet?

Thank You USPS

So after a year of waiting I finely got my official BL daggerboard push rods from the supplier. You may recall that last year I used a push rod made by a local machine shop. That rod worked fine but it was damaged in, um, lets call it an industrial accident. So I got two rods and they showed up in a flat box. As soon as I saw the box I knew something was wrong. The USPS had bent the roads in shipping in several places. Luckily I was able to call the supplier and they agreed that rods probably hadn't been packaged sufficiently to make the trip and are sending replacements. In the meantime moth repair continues, but I fear that the moth is going to be ready before the weather is...

Bulkheads

To help out the few people who may actually try and build one of these things I’m going to offer up some more design details. One of the cool things about this method of using the stressed and bent plywood hull is that the general shape of the plywood skin pretty much defines the shape of the whole boat. The only real thing that you can change is the width of the deck at different points and how much V you want in the bow. Once the hull is stitched (or taped) together and you can bend it into whatever shape looks good to you. Rather than pre-defining the bulkheads and then forcing the hull to fit that shape, I let the shape of the hull define the shape of the bulkheads. So here’s all you really need to know, the deck width at the mast is 260mm, the deck width at the stern is 355mm, the max deck width is 370mm, and the front of the daggerboard box is 1525 mm from the bow. The V in the deck is 45 mm deep (at the mast). Note that Mothball one is slightly different than what I’m giving you here, but if I were to make it again this is what I’d use. The changes are small but would probably make a better boat.

So if you set those three deck widths it’s time to start making bulkheads. Bulkheads are really pretty easy to make, especially using the same thin ply used for the skin. You can cut out a bulkhead in about 60 sec, but the shape needs to be well defined. Mothball One has 11 bulkheads (including the solid transom bulkhead). Nine bulkheads are in the deck area and two are in the bow. Most of bulkheads have an inverted Y shape cut into them to reduce weight. To define the shape of the bulkheads measure that area on the boat as best you can and then draw the rough bulkhead onto a piece of cardboard making sure to make the bulkhead as square and symmetric as possible. Put the cardboard bulkhead in the boat and then trim it to make it fit as best you can. Then take the cardboard bulkhead and use it as a template to draw the plywood bulkheads. Again make sure the plywood bulkhead is square and symmetric. The skin will define the overall boat shape, but the bulkheads will ensure that the shape is square. If I were to do it again I’d probably add one additional bulkhead near the middle of the boat because that’s where the sides get stepped on a lot after you take a swim. Also note that the bulkhead below the mast should be solid to help create the two separate airtight tanks as defined by the Moth class rules. The daggerboard box has a bulkhead on each end of the box for added strength. Take a look at my older posts for some bulkhead pics.

Design Drawing

I've had several inquiries about the design for Mothball 1. I have no problem with giving out the design details, but it wasn't in any form that I could easily digitize since it was all on paper. Finely I just decided to take a picture of my large hand drawing and then clean it up with a photo editor. Here's what I came up with. It looks reasonably good I guess. If you want to see how it all goes together just print this out on some card stock, cut it out, fold along the thin red lines and then tape the edges. If anyone wants to take this and make it into a formal CAD drawing, feel free. I'd be happy to answer any questions about the design.

Down For the Season

Unfortunately the sailing season is Montana is somewhat short, this does make for a good skiing though. Mothball One has been mothballed for the season. The last time I sailed I damaged the main foil again and found a crack the the mast base. Not huge problems, but I didn't have time to fix them and decided to just wait till the spring. The plan is to fix all the problems and have her ready to go when the ice comes off in April. It was a fun year, learned a lot, can't wait fly again, but flying over the snow has its merits too.