Replacing rotted rudder with marine grade plywood coated in fiberglass

[Cheechako]

Well... we haven't heard back fro the OP. But I'm assuming he's using plywood because it's an outboard hung rudder with no metal shaft. I think it's a good way to go for that.... properly covered and saturated.
Fiberglass rudders I have had with a shaft going into the glass have leaked and got water in them. It appears to me that trying to seal fiberglass to a shaft does not work. One was a 92 boat and was waterlogged by '98. 6 years. For all I know it was waterlogged after one year.

[SVJennie]

My inboard 2 inch thick plywood laminated rudder is still going strong after 40 years as well, and that is even after the stern strap of a travel lift thought the rudder was part of the keel. The only damage to the rudder was the top of the rudder stock being bent which I straightened using a hydraulic jack and an I beam.

As for fiberglassing, the previous comments regarding saturating the wood are well founded. As for the weight of the glass, the main purpose at this point is for abrasion protection, not strength. Accordingly, I found a couple of layers of 7.5 ounce to be more than adequate.

All the being said, sealing the rudder stock and ply from exposure to water is very important. You might consider filled epoxy cofferdams at these points.

Since I don't know the size of your rudder, I feel mine requires a bit of imagination for me to remove and replace because of its weight. You MIGHT consider allowing non-structural internal areas to be filled with foam. Think of the ribs of an aircraft wing.

Good luck!

[adlib2]

Originally Posted by Shore Footed

I am in planning stage to rebuild my rudder. I've watched videos on fiberglassing process. My dilemma is in choosing weight if fiberglass and amount of layers for durability. My plan is to sandwich 3/4 " plywood then use original as template. Original is 1 3/4 " thick which leaves room for 1/8" shell of fiberglass. Any help or direction would be greatly appreciated.

Shore Footed is an appropriate Handle since I've owned boat for about a year and have yet to be able to take her out of the slip!!!

You have many naysayers and so did I when I rebuilt my rudder using a wood core. But I did it with small interlocking laminations, and that was 6 years ago and giving good service since.
They're many others done the same. Use copious amounts of epoxy to seal the inside wood and use a an FRP sleeve where the rudder stock enters the rudder also well sealed with epoxy.
I got fed up rebuilding the rudder which I did 4 times before I rebuilt with wood core. Those naysayers have never done it, just rolling out established OME practise and about leakage and wood swelling. If the wood is adequately encapsulated in resin how can it take in moisture?
I uploaded many photo's to an Irwin Group Site during construction.

[patn44]

Built a ply/glass rudder, actually two for two different Catalina 22 boats. Worked fine. 3 layers of glass on after saturating wood with epoxy.

[Wotname]

This is a good time to remind the OP that all marine plywood is not created equal; in fact there can be big difference between various manufacturers of marine ply.

Presumably the OP is North American based and while I'm not familiar with their suppliers I suspect it is similar to the Australian market.

Here the two main specifications are the British standard BS 1088 and the Australian standard AS2272. While the Australian standard produces a far superior product to that of the BS 1088, it is (again presumably) not available in North America. So the OP is left with getting the best product he can under BS 1088 or any North American standard.

Be aware that the BS 1088 stamp is sometimes forged or otherwise not meet by some less scrupulous manufacturers.

All genuine marine ply will a type A bond (waterproof glue), both face veneers free of defects, all veneers to be a "rot resistance" species and less than 5% voids in internal veneers.

The better plys will have a single species used on all veneers and way less than 5% voids on internal veneers (and minimal other defects). While price can be a guide, it is of course, no guarantee of quality except to say, the best marine ply is never cheap .

For a fully submerged reasonably sized rudder, I would be sourcing the best quality ply I could in my area and use normal epoxy techniques. As others have posted, the glass is really only abrasion protection and as a medium to ensure a decent thickness of epoxy.

Edit: Although epoxy is the best coating, these days I would be happy to use other products for gluing during the construction phase e.g. a waterproof expanding polyurethane or the old (& unbeatable), resorcinol - if your wood working skill are good enough.

The polyurethane allows for quick(ish) curing and is very tolerant of voids when fitting the components together however it must be well clamped during it's short curing phase.

I doubt there is any over the counter product that is stronger or more waterproof than resorcinol but it is completely intolerant of voids and also must be well clamped.

Of course, epoxy is great for strength and waterproofing, reasonably tolerant of voids and should only be lightly clamped. The downside is the longer curing times, hard to work when cured and the general mess

[Nicholson58]

Originally Posted by nauticalnomad

Check these guys out...
Jefa Rudder bearings

Another source: igus® - iglide® Plastic Bushings These are cheap by comparison. My 2-1/2 inch bottom bearing replacement cost me $7.50.

[paul k]

My experience a year ago . My Simpson 12 cat came out for antifoul only to find that there was little damage to bottom leading edge of rudders. They were made of red cedar glassed over. When cleaning up for a patch found wood worm had gone right up through rudders .Our local boat builder rebuilt them foam sandwich. They are fearsom creatures in a wooden boat. Have become obsessive with regular mask on underwater inspections.

[Sailorbob8599]

Originally Posted by Wotname

Marine ply is fine for a rudder if properly built (and maintained).

FWIW, my ply rudder is still giving good service (touch wood) after 40 years of being submerged.

Thank you Wotname, saves me adding my five cents worth to this discussion.

[odonnellryan]

Purchased my Catalina 25 with an "extra-thick" rudder: about 2" of marine(?) plywood. Painted, not glassed over.

Worked for a while, but we liked to push the boat. Rudder broke during a bad time, but luckily no one hurt or overboard and the boat didn't end up hitting anything.

Upon examining, it was discovered that there did not seem to be any or much water intrusion into the rudder from what we could tell (only had the top half of the rudder left).

My thought is that the wood was just a bad choice. Don't use plywood would be my suggestion.