Saturday, April 30, 2011

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?

2 comments:

Kirk said...

In addition to the gearing effect, the point of contact of the wand makes a difference in how much it senses the contribution of pitch and height. The wand is controlling two degrees of freedom with only one variable ( lift). If the contact is too close the main foil then it cannot "see" the pitch of the boat....which leads to pitch instability.

Bob Abelin said...

That's an interesting point Kirk. I can see how having the end of the wand too close to the main foil would cause pitching problems when the boat is low in the water. I think a bent wand could actually reduce this problem by moving the sensing point forward to the knuckle when the wand is up. Maybe you'd even want and extra float at the knuckle. This idea is sounding better and better.