Laminating a rudder

[John Stevens]

I'm going to make a rudder from 1" x 3" fir. I will be laminating the fir face to face. Can I use a good waterproof glue? If so, which glue do you advise? I will epoxy the outside when I'm finished.

Also, can I use ss screws to hold it together or do I have to use bronze?

TIA,

John

[capt jake]

Uh, why not use slightly thickened epoxy??? Waterproof, no screws or nails needed. Just don't over-clamp it.

[mrthethird]

The DAP Weldwood Plastic Urea Resin glue is a good choice, will handle the stress well and is waterproof. Need to clamp it good and tight, though.

The epoxy would be a good choice, too. Just don't clamp it as tight as the plastic resin glue. Don't want to squeeze it all out. Yadee yadee ya ya....

As for the screws, I would think stainless steel should be fine, especially since you are covering the finished product with epoxy as well, but I'm no tto that point on my boat yet :oops:

[John Stevens]

Why do I need to clamp it if I'm going to use screws?

I had planned on drilling holds and setting the boards up before I'm ready to glue. When I have the fir pieces cut and ready I'll glue and screw in place. Does that sound right?

John

[Charlie Jones]

That'll work John, perfectly well.

[John Stevens]

Thanks all!

John

[John Stevens]

Will there be a problem with using the ss screws? Why did I need to use the bronze when I made the pram?

TIA,

John

[Frank Hagan]

There is always a worry about crevice corrosion with stainless steel that is held in water that can be deprived of oxygen. If there isn't a supply of fresh water going past the stainless, it can corrode very quickly.

The alloy in stainless steel reacts with oxygen to form the film on top of the metal that protects it from corrosion. In doing so, it "uses" a bit of the oxygen. If water seeps in next to a stainless screw, for example, the water is trapped next to the metal, and the stainless alloy "consumes" enough of the oxygen that the protective film is diminished, but not enough to prevent corrosion. So the stainless screw corrodes very quickly. On boats, this is most often seen in places like the bilge, with keel bolts or fasteners on thru hulls, or on clamps and that sort of thing where a "crevice" in the design has localized corrosion.

Once stainless starts to corrode, and that protective film is compromised, the corrosion will continue even if oxygen is restored to the area. The mettalurguists call this "auto catalytic and self propegating."

Michael Kasten has a pretty good article on using fasteners in wooden boats, but again, his focus is on a boat that is in the water all the time. See http://www.kastenmarine.com/metalparts.htm for his article.

A lot of what we worry about on boats doesn't apply to a trailer sailer. Your stainless screws that are encapsulated under a thick layer of protective epoxy on a tiller (I.E. above water line) will probably never see any moisture. If they were below water line on a boat that stays in the water a lot of the time, I think there might be reason to worry.

[Charlie Jones]

Use the stainless John- they'll be buried in the wood, buried under epoxy and buried under glass. Not a problem.

Otherwise, as Frank says.

[John Stevens]

Thanks again all!

John

[John Stevens]

I've been looking for the DAP Weldwood Plastic Urea Resin glue but can't seem to find it. Can I use something like Tightbond 111 waterproof glue?

I'll be putting epoxy over the rudder.

TIA,

John

[Frank Hagan]

I've been looking for the DAP Weldwood Plastic Urea Resin glue but can't seem to find it. Can I use something like Tightbond 111 waterproof glue?

I'll be putting epoxy over the rudder.

TIA' date='

John[/quote']

I wouldn't use the Tightbond III; I'm just not sure it will work for long term water immersion. A lot of the "waterproof" glues for outdoor construction are really designed for above-ground outdoor construction. That being said, I think there are some strip kayak builders using it for thier boats (they glass and epoxy coat over it).

In this case, since you are going to use epoxy over the top, I would use epoxy as the adhesive for the laminations. You can use the thicker ones like RAKA and SystemThree straight, or mix in a little of one of the thickening agents (wood flour, collodial silica, etc.). For the thinner epoxies like MAS, you would need more thickener, I think. You still clamp the pieces together, but just make sure you don't squeeze out too much of the epoxy mix. If you are a "not so great" woodworker like me, you like the idea of ripping the pieces on a table saw and going straight to glue-up without worrying about jointing the edges!

Most of the amature boat builders today just use epoxy for their adhesive needs. You can get into some hard to find glues like resorcinol, but there's really no advantage.