|
A spade type rudder has a lot of advantages for performance. It is easier to balance and has higher lift but it has one big disadvantage over skeg hung types. It is vulnerable to any obstruction that makes it past the keel. To compensate, it has to be very strong.
John recommended a composite stock but at first I balked at the cost. I started looking for alternatives. Heavy wall 316 stainless tubing seemed like a good choice but the cost with machining was not that much less than carbon and the weight would have been almost tripled. As the rudder is only about 3' from the stern, the lever arm would give any extra weight a lot of momentum. Titanium would have been lighter but the cost was more than composite.
There was also the problem of resilience. If I did hit something, a metal stock would bend and stay bent while a composite stock will take more deflection and return to its normal shape. Finally, metal tubing would have to be the same diameter for its full length. Composite can be shaped and tapered to optimize the balance between aerodynamic shape and strength.
 So I was finally convinced. The stock will be supplied by Aerodyne in South Africa. At the lower bearing it will be 140 mm thick. I didn't really appreciate how big 140 mm is until the bearings arrived.
This is a set of upper and lower self aligning rudder bearings from JP3, a French company that specializes in steering systems. You don't want to know what it cost! Let's just say that worry about the cost of the stock was misplaced.
JP3 was very good to work with though it did take a bit of explaining when my wife took a message from a sexy sounding woman calling from France.
The bearings have about 5 degrees of movement so the will align with the rudder stock as it flexes.
|
CCW from lower left: Composite housing for lower bearing, lower bearing, upper bearing, locking collar, upper bearing sleeve, lower bearing sleeve
|
|
The first challenge was chopping a 9" hole in my precious hull! "Measure twice and cut once." was an under statement. The rudder bearing area had previously been reinforced with solid glass but I spent two days verifying the center line, reestablishing the station marks, checking vertical angles and building up my nerve. 
The tapered composite housing was slid in from below the hull and glassed in place. Then the extra skirt was trimmed off flush with the hull. To keep the housing from distorting, I had to do the glassing with the very expensive bearing bolted in place. Needless to say I used a liberal amount of masking tape. 
T h e t o p b e a ri n g p r e s e n t e d a d if f e r ent problem. It came with a flange to be bolted to the bottom of the cockpit deck. But the rudder stock is angled at about 15 degrees forward and the cockpit is angled about 2 degrees backwards. I had to make up a wedge shaped block to keep the bearings within acceptable alignment. I built it up from wedges of marine plywood and then had to find a way to cut a true hole. The only way I could figure out was to rough cut it with the jig saw, drum sand a little over size, coat the bearing with PVA and use it as a mold to pour epoxy in the gap. It made a perfect fit.