I needed to replace the gudgeons on my Hobie 18 because they were bent and the holes were slightly oblong, they were causing stress and wear in one spot on my fiberglass rudder pins and causing them to break often. I decided to replace the gudgeons with the single piece gudgeons.
The single piece gudgeons come with aluminum rudder pins with cotter pin holes in the top and bottom, but I am using fiberglass pins because I sail in the ocean and often through surf. The issue I am having is that the fiberglass pins I have do not seem to be long enough get a cotter pin above and below the assembly like is illustrated in the directions. Are there longer fiberglass pins for use with the single piece gudgeons or should I drill cotter pin holes in the pins to secure them inside the gudgeon instead of above and below it?
I had a 1986 Hobie 18 and used to have fiberglass and switched to the aluminum pins. If you bought your supplies from Murray's, then the pin length should have been right. If you want longer pins call Murray's. The idea of drilling holes on the bottom is a pretty good idea. Does your Hobie 18 have the lip on the top of the hull? Meaning......if you push up on the pin.....is there any way for it to come out? On my Hobie 18 there was a lip and the pin could only be installed from the bottom, so I only had to use one pin for the top to keep it from dropping out the bottom. I hope that helps.
Like delaunhe said, you should only need one pin since the deck lip prevents the pin from moving up too far.
I'm guessing you are using the fiberglass pins because you are afraid your rudders won't kick up when beaching? On my '81 I used those when I was having a lot of trouble with the old style rudder system staying locked down and broke a couple of castings and even pulled the stern out once.
However, after I had a fiberglass pin break (without hitting anything) while I was sailing along I realized that it might be better to suffer possible damage than lose the entire rudder system. Now I use stainless pins, because they remain straight longer. Even the aluminum ones get a little bent and become very hard to remove.
The pins are the only things that attach the rudder castings, rudders, tiller arms, tiller cross arm, and hotstick to the boat! If both fiberglass pins break (once one breaks the other will get torqued off) the whole system could end up on the bottom.