There's rudder stuff on the history channel here. Punch Search if interested.
338's clam shell rudder has just been reactivated.
Basically the top third of the blade comes apart, held by a keyed channel on the post with three bolts. On the trailing edge the shell is held with 4 machine screws.
The rudder post is silicon bronze, as are the 1/8" straps, as are the fastenings. as is the welding wire. The idea of course was to get all the metal parts the same to avoid galvanic action. That was fine until Bristol admitted to casting the shoe in manganese. I had a discussion with Bristol about my rudder - the upshot being that silicon bronze is too soft for the job. Bristol said they supplied Pearson with rudder stock in the Ariel days and it was manganese. Roger said that while made from manganese the rudder would last 150 years my silicone one was only good for fifty. Silicone is 98% copper.
Hell, I attached the Bristol shoe to the rebuilt heel of 338's keel with peened over silicon rod and it seems to be showing some corrosion with crusty bright green weeps. The boat has been out of the water for more than two years and its showing signs of corrosion!!! It's obvious that there still is saltwater in the laminate in the aftend of the keel. But we do have two bronzes reacting. Out of the water! They're holding hands in the galvanic series.
The take apart design (the idea is not to have to raise the boat) requires more metal I think than a straight welded rod and strap. I had to kind of double the strapping in the two-part clamshell area. A plain welded strap to the shaft design IMCO is a good alternative to having holes drilled in the rod for the bolts in the wood version. Altho there has been no problem with this design, I understand. except aging. With the 338 rudder I used a rigid closed cell expanded PVC foam (Divinycell) to fill the spaces. Setting it in with epoxy gell.
I'm just about to do the glass work. But keeping the take apart option makes the glass work very difficult and takes away from the massive strength gained with sheathing the whole blade with glass around the rudder post. To be able to still take it apart the upper third would be split along the rod and, of course, split to the clam shell. I need a chunk of time to ruminate on the complexity to have it come out ok.
Even so, I'm not happy with the small fastenings holding the design together.
If you did not build your rudder out of polyester and urethane foam like the production boats (C'pete's survey report) but used PVC foam and epoxy, I think the rudder would be waterproof, taking in very little water, depending on the workmanship.
[Weight wise, this is a heavy rudder. I think it will turn out to be much heavier than mahogany with a bronze shaft. I also think a recreation of the original rudder will enhance the value of the boat, while a composite or trick rudder might detract.
On the other hand a bronze rudder post (rod, shaft) with welded bronze strap (rolled sheet) developed into an efficient grid that comes to a more pointy trailing edge than the woody - with hard closedcell foam, epoxy and frp (not carbon fiber which is too distant on the galvanic scale
from bronze) - would be most desireable and nearly indistructable.]
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