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post #11 of 18 Old 05-05-2009
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Plywood rudders work quite well for pindle and gudgeon hung rudders with the alternating plys distributing the loads both vertically and horizontally. They should be shaped to get decent flow and beefed up above the waterline so that the torque is fully distributed into the foil. They do need to be sealed with epoxy and ideally with a layer of cloth.

For any sizable boat the rudder would need to have a thickness of roughly 1.5" (40mm) to 2.5" (60mm) thick. And there is the problem-properly engineered it would be extremely heavy and difficult to ship. Beyond that the pindles and gudgeons would need to be very sturdy and the transom beefed up to take the huge loads.

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post #12 of 18 Old 05-05-2009
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I agree, the stock rudder on my boat I believe is marine plywood.

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Plywood rudders work quite well for pindle and gudgeon hung rudders with the alternating plys distributing the loads both vertically and horizontally. They should be shaped to get decent flow and beefed up above the waterline so that the torque is fully distributed into the foil. They do need to be sealed with epoxy and ideally with a layer of cloth.

For any sizable boat the rudder would need to have a thickness of roughly 1.5" (40mm) to 2.5" (60mm) thick. And there is the problem-properly engineered it would be extremely heavy and difficult to ship. Beyond that the pindles and gudgeons would need to be very sturdy and the transom beefed up to take the huge loads.

Jeff

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post #13 of 18 Old 05-05-2009
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Dog,
Is it the plywood, or the fiberglass covering that gives your rudder it's stiffness?
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post #14 of 18 Old 05-05-2009
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The plywood... but my boat is relatively small and light.

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post #15 of 18 Old 05-05-2009
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I think the longer ocean races now require the boat to have an emergency rudder aboard and to have mounted it under non emergency conditions, so more people have been thinking about the subject.

I have been eyeing the bottom of my pilot berth. It is currently made of 1/2 in plywood but if I upgrade it to 3/4 and reinforce it with fiberglass cloth and epoxy it would be solid enough, especially since at least 1/3 of its 6 1/2 foot length would be out of the water. I'd have to get some pretty heavy gudgeons and permanently install them and predrill the rudder for pintles.

It's on the "to do - (eventually)" list.

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post #16 of 18 Old 05-05-2009 Thread Starter
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my basic idea it to make it out of 3/4 ply ( with a glass layer ) the size of one of my settees for storage. then a handle which would bolt on, then slip in to some mounts on my stern which is 1 inch thick glass that i have 100 % access to for backing plates. it would not need to be off shore, just get to shore in the bay

i think i may do it
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post #17 of 18 Old 05-05-2009
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Rudder Emergency

Marine plywood / epoxy would not be neutral buoyancy - although it probably wouldn't be of top concern in a lost rudder situation, Handling would be very different from a rudder with proper buoyancy.

The force on a hard over rudder at hull speed is measured in tons. Hose clamps and a boat hook attached to a barn door will be very exciting, and tragically, almost useless.

The best bet is to have safety straps (they can double as stops) external to the rudder. If it falls off, you can get it back.

Best Regards,


e

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post #18 of 18 Old 05-05-2009
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Just to add another example of wooden rudders:

My boat a C&C25 has a solid wood laminate rudder. I say laminate because it is nothing like the plywood we might commonly think of. I have no idea how old this rudder is or who made it originally but it is made from a very hard deep red wood, perhaps Cyprus or Redwood. At the top (tiller end) it is 2.5" thick and tapers as it meets the water line. The leading edge is tapered as is the trailing edge. The trailing edge has a much wider taper than the leading edge to make it more of an airfoil. The layers of laminate wood are of varying thickness; (see photo). Where the laminates are tapered there is extra layers of glass cloth buildup as well as on the leading edge and bottom foot of the rudder. The whole rudder is encapsulated in a thick coat of epoxy resin.

I recently sanded it down to bare glass and re-coated it while I was replacing the gudgeons and pintels. I had to trim a small area of the rudder with a saw and was able to see the laminates very good in the cross section.
The rudder is very heavy for its size (about 5' tall) weighs 50lbs. I'm hanging it on a new set of Shcaffer transom mounted gudgeons and the pintels are 1/2 inch heavy duty custom stainless steel.





Just thought you guys may be interested.

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C&C 25 MKI, Hull No. 039
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