Tuesday, July 06, 2010

Steering a course

I've temporarily bolted on the Gudgeons, I'll take them off again to epoxy the holes, and for painting. But I need the Gudgeons for 2 reasons.

1) I will need to go fetch my mast, so I will need the trailer lights mounted, which will mount onto the Gudgeons.
2) I wanted to make up a test rudder.

I was in two minds about a kickup rudder, see the diagram at the bottom of this Glen-l Letter page. And I want to test out my planned method for creating the foil. Both begged for 2nd rate plywood rather than the expensive stuff.

I drew and cut the rudder as shown in the Glen-l Letter, and then made up the cheeks with 6mm ply. I used a large bolt for the pivot. All went very well. I think I'll laminate up 2 x 6mm ply for the cheeks of the final rudder.

So then I went on to the rudder release.... If I hit the bottom I don't want stuff to break, so I tried out one of the Auto-Release Cleats from Duckworks. See http://www.duckworksbbs.com/hardware/cleats/sd002570/index.htm

Be warned, the angle of the lead makes all the difference in the world to how hard it is to pop the cleat. Since my clear was on the cheeks, and the line lead to the rudder, 6mm or so "lower". The line lead "up" to the cleat.

A quick decomposition of vectors later with a pen an paper confirmed that if you lead "up" to the cleat from below, it simply won't pop open, it's not the fault of the design, simply basic geometry. Smacking the rudder off the ground to simulate hitting an underwater obstacle simply dented my rudder (this is a mock up - so that was no big deal.)

I tried a simple sacrificial wooden pin (a disposable chop stick) and I got much better results, but it would be impossible to clean out the broken "pin" and replace it under way. So I need to experiment with the auto-release again, now that I understand why it did not open. (Yes, I had it set to the minimum resistance setting)