RE: RC Surfer
The rudder steering arm I am using is off an old airplane steering arm. The one you are looking at on eBay should be fine. Just remove the grub and file down a 3mm screw and that way you can use a pair of pliers to tighten it up.
Remember to file the side of the rudder strut so the screw sits against a flat area on the rudder strut, see pic.
I used a 4mm tube and pushed it in the rudder slot and marked where I needed to cut it. Now you will need to find a bullet plug and cut the end of it off and slide it on the rudder strut so it fills the end of the propshaft tube that is cut. Once you cut it, you will see that the uncut end is 4mm and the cut end is 5mm, the little ring of brass from the bullet plug seems to fit perfectly over the rudder strut and nicely into the propshaft tube. This will give it a good seal and you can fill the tube with grease.
To make the fit, get the 4mm propshaft and file down 2 sides of the threaded end, cut a fin out of plastic (I bought a plasters tool to smoothen out plaster, 2 bucks from bunnings) and cut the slot for the rudder strut to go into and used super strength shelleys epoxy to set it in place. Make sure the rudder strut is set further to the front of the rudder than the centre or it will have to much force on it to push the rudder back to center after a turn.
Then fiberglassed it in with laminating resin and cloth then painted then filler coated it. It is the same as the fin for my larger home-made surfer and is just as strong, just a little smaller.
Once the tube is in place (a little superglue will keep it firmly in place and side in the rudder and into the steering arm and mark where to cut it. Once you are happy with the rudder and tube, file down the rudder strut where the screw will tighten against the rudder strut. MAKE SURE YOU HAVE THE SERVO CENTERED AND GET AN EVEN LEFT AND RIGHT TURN BEFORE YOU MARK WHERE TO FILE DOWN A SPOT ON THE RUDDER STRUT.
Try it out with out a horizontal wing inserted, it might be perfect for you. If you do want to fit in wings, just get a hacksaw blade, snap a 2-3cm piece, heat it up and push it through the rudder. Make sure it is at a slight downwards angle.
Hope this has been helpful.
I wish you had a helmet cam, between you, John in Maui and I, we would be able to put up 15 minutes of footage to watch each week!