Having this week made a trip from Auckland, to Waiheke, to Great Barrier, to Kawau and now night-sailing back into auckland, it's a good time to update this thread on design progress.

The was noticing that the steering was getting a bit sloppy, and indeed the control fin would not just yaw but also roll. Examining the bit where the control fin pivots on the lever end - it was badly worn!

The bearing is a stainless steel bolt directly on a pretty thin walled aluminium tube, and aluminium is pretty soft so it's not surprising. I tried fixing this by rotating it and drilling another hole, but later realized that the original drill bit had broken at some point, and the new hole was oversized, so same problem. I found a hard(ish) plastic tube that fit snugly between hole and bolt... but the pressure between the bolt and the tube cut it, so I tried filling the end with an epoxy plug.

I used some rubbish as a plug, then poured epoxy into the end.

When that went hard, I had a working self steering again!
I was sailing with that from Kawau to Waiheke, and everything was going pretty well, then dolphins came (at night again - saw dolphins 3 times on this trip!) and then suddenly I noticed that the control fin was rolled way over, then I saw it barrel roll right around the lever!

I pulled it in and the bolt had snapped. Did a dolphin break it?
Anyway, I managed to get the snapped bolt out by cutting a groove in with the hacksaw and turning it with a screw driver.

Clearly, the control fin pivot is the most highly stressed part!
It's a fin about 500mm tall, canterlevered off a 6mm bolt going through 25mm tube. If that was a 50mm tube, it would be a lot better, with some sort of sturdy bearing... Solid plastic, and a thicker bolt... The level is also under torsion, so something with a higher cross sectional area will make that stiffer.

I want to not have to fix something every 50 miles!