rebuilding a rudder and boom question

Rxboat · #1 10-10-2012

I will need to make a new rudder because the old one got water under the fiberglass and water logged and rotted the wood. The boom for my sailboat is basically a 2X4, 11ft long, too badly weathered and has splits and sharp edges all along the groove that holds the sail - these could cut or tear the sail. So I need advice on materials to use for the new pieces.

The rudder I plan to make using plywood doing a lot of sanding in order to shape the thickness and then cover it completely in fiberglass, then paint it with white gel-coat. My question is can I use a (I will not use any pressure treated plywood) such as AC exterior grade plywood instead of marine grade plywood in order to save money on the cost of the plywood since I will be encasing it in fiberglass and painting it anyway. The plywood will have voids when I am finished planing and sanding it to shape, but these will get filled up with the resin and fiberglass.

The new boom I will make using either cedar or redwood (because these are somewhat resistant to water) then paint it with white gel-coat or marine paint. I don't know if these are the best woods to paint over, I hear they have natural oils that tend to make it harder for paint to adhere well over time. Any thoughts about these plans I have?

Faster · #2 10-10-2012

I'd use epoxy resins rather than polyster, esp if you're not going to use real marine ply for the rudder... and then simply paint it with a decent paint once you've removed the post-cure amine blush.. Epoxy is more water resistant than polyester resin, esp in thin layers.

I wouldn't try to 'gel coat' a wooden boom.. just paint it - you'll be needing to touch it up periodically anyway, so why make it complicated? Or leave it natural/varnished/cetol'ed or whatever...

JackandJude · #3 10-10-2012

I agree wholeheartedly. Do Not use polyester, which is fine for laminates upon itself, but does not soak into wood anywhere like Epoxy. Dilute the first coat as recommended. Over here in Australia, all exterior ply uses "A" bond glues, the same as marine ply. The difference lies in the heartwood plys, which in exterior can have knots and small voids, whereas marine grade layers are all first grade.
I'm not a great fan of plywood rudders even if epoxy coated, choosing solid timber instead because plywood sucks up water and breaks down much more quickly than solid. I'm thinking of a break in the sheathing, a nick, dent, whatever as time goes on. Oregon is frequently used diagonally laid, epoxy glued and bolted.

Re your boom. Again a good quality enamel will be better. It's more flexible than polyester, easier to recoat, and does not break down so quickly with UV.

Or use a durable number one timber and let it go grey.

PS: My first rudder was polyester sheathed, which split and allowed toredo worms in. First I knew of it, my rudder seemed wishy-washy and when I dove to inspect, the whole damn thing was flopping about on its fixings!

Jak · #4 10-10-2012

Not sure about redwood, but cedar is a very weak wood, i do not think i would use it as a boom

Jak

CalebD · #5 10-10-2012

Isn't Sitka Spruce used a lot for spars?

Lake Superior Sailor · #6 10-10-2012

Would be nice to know what you are working on ! A dink or what? ...Dale

JackandJude · #7 10-10-2012

Sitka Spruce has been spar material for years, as has Oregon (Douglas Fir). Forget Redwood or cedar, way too soft and lacking strength.

Rxboat · #8 10-11-2012

Thank you all for the great information. I will see if I can find a solid piece of wood for the rudder instead of plywood(measures 14" X 39").
I will look for Oregon (Douglas Fir) or Sitka Spruce for the boom.
This is on a Finn sailboat, probably 1980's, don't know the year of mfg. I'm looking forward to next summer, hopefully, when it's ready for the water.

JackandJude · #9 10-11-2012

I'm going to revise my advice now that I've read it's a Finn, a small vessel, and say go with the plywood. I did find on another site the email address of the class secretary. You might ask them what is recommended. secretary@finnuk.org.uk
Cheers,

SloopJonB · #10 10-11-2012

Quote:

Originally Posted by Rxboat

I will need to make a new rudder because the old one got water under the fiberglass and water logged and rotted the wood. The boom for my sailboat is basically a 2X4, 11ft long, too badly weathered and has splits and sharp edges all along the groove that holds the sail - these could cut or tear the sail. So I need advice on materials to use for the new pieces.

The rudder I plan to make using plywood doing a lot of sanding in order to shape the thickness and then cover it completely in fiberglass, then paint it with white gel-coat. My question is can I use a (I will not use any pressure treated plywood) such as AC exterior grade plywood instead of marine grade plywood in order to save money on the cost of the plywood since I will be encasing it in fiberglass and painting it anyway. The plywood will have voids when I am finished planing and sanding it to shape, but these will get filled up with the resin and fiberglass.

The new boom I will make using either cedar or redwood (because these are somewhat resistant to water) then paint it with white gel-coat or marine paint. I don't know if these are the best woods to paint over, I hear they have natural oils that tend to make it harder for paint to adhere well over time. Any thoughts about these plans I have?

Cedar & Redwood aren't great choices for a boom. They are a bit brittle. I'd use Douglas fir if you can't get some good Spruce. Varnish is better than paint in this instance because it lets you see any problems developing in the wood. Paint hides those problems.

Faster has it right about the rudder.