Shearing rudder nylon safety screw

[JonD]

Further to my recent post regarding Rudder Pick up and Water Cooling Problem on my Genesis, I now have plenty of water flowing by increasing the size of the inlet slots at the bottom of the rudder (and removing the cooling from the front motor mount), but the 3mm Nylon safety screw (that is presumably there to stop you ripping the back of the boat off should the rudder hit something) is shearing, seemingly by itself without hitting anything, when at high speed. Last time I caught it before it sheared right through. It happened yesterday, and again today.

Rudder nylon shear pin.JPG

I don't think I hit anything or I would have expected it to shear right through. To me this looks like too much pressure on the nylon screw.

Could this be caused by the mods I did to the rudder, that is causing a lot more resistanse and drag in the water? Seems hard to believe it could make that much difference. Before and after photos below.

Rudder mod.JPG

I have the main 4mm screw that the rudder pivots on, fairly loose and it does pivot quite easily (when the nylon screw is out). Should this screw be tighter?

Has anyone else had this nylon screw shearing in normal operation (i.e not due to the rudder hitting anything)?

I could go to a 4mm nylon screw but I am reluctant to do something that may result in damage if I do hit something and the screw doesn't shear when it should. Or perhaps I have just screwed up and should have left the rudder as it was -but it seemed worth trying at the time. Also, the suggestions of replacing the hinge with a brass tube prop wash pick up, or even the separate water pump seem to have plenty of merit.

Not sure what to do now Any ideas?

Jon

[LarrysDrifter]

Snug up the 4mm bolt. It doesnt need to be loose. Your hole enlargement might be causing a bit more drag, but not enough to shear the shear bolt. With the big bolt so loose, most of the pressure is being put on the nylon bolt. I have found that the nylon bolts on the cheaper made boats are a bit more brittle than what you can buy here. Even a local hardware store might have a higher quality nylon bolt that fits your rudder.

[longballlumber]

Another option would be to replace the nylon bolt with a brass bolt/screw. It's not going to shear as easily as the nylon, but will do the job if you hit anything.

Later,
Mike

[BHChieftain]

I keep the pivot bolt on the rudder really tight myself-- I've hit debris several times and the rudder still pulls back just fine (shearing the nylon bolt).
Chief

[sailr]

I agree with everything above. By leaving the pivot bolt loose, you are allowing the nylon screw to be SHOCKED by constant bouncing back and forth. Tighten up the pivot screw! I have also gone to brass screws and they work well.