Wooden boat Varnish/epoxy

[JordieS]

I've been reading some builders threads and they seem to coat the exterior of their hulls in epoxy then varnish or clearcoat. Why do they need to coat in epoxy? Can't they just apply lots of varnish, after all isn't varnish waterproof? Is it absolutely necessary to apply epoxy and all that?

Am I missing something?

Thanks

[michael pierzga]

You could simply varnish a wooden boat. Then strip the varnish off, sand and re varnish next year, then next year, then next year, then next year................

The epoxy base is more durable , hardens the surface and is more waterproof hence it will last many years until you must strip, sand back and refinish.

In general its not wise to clear finish a boat... the construction needs the very best material, the best workmanship because every detail is visable, and its very high maintenece.

You were considering a strip plank boat. In my opinion strip plank boats look terrible with a clear finish. Trip diagonal construction with the last layer laid as " Planking " fore and aft looks good clear.

[JordieS]

I was just looking at the different types, I think I will do cold molding apply a stain and then epoxy and varnish etc

[michael pierzga]

The designer Paul Gartside designs very elegant, highly detailed multi skin wooden boats. You might swing by his web site , do some reading or even purchase a set of his plans to gain insights for your own design.

http://www.gartsideboats.com/faq/pla...mparisons.html

http://store.gartsideboats.com/collections/power-boats

[JordieS]

Ok thanks for your help, but instead of buying plans I am going to build a small model boat to get a bit of building experience and designing myself.

Thanks once again

[michael pierzga]

Building models is a great way to get a feel for construction and design challenges.

The advantage in purchasing a set of plans from a reputable designer is that for 300 or so dollars you gain the results of the designers years of training and construction experience.

This FREE knowledge contained in the construction plans allows you to leapfrog common mistakes then produce an OWN DESIGN that better serves your requirements by reverse engineering the professional poduct.

[Eric Sponberg]

Originally Posted by JordieS

I've been reading some builders threads and they seem to coat the exterior of their hulls in epoxy then varnish or clearcoat. Why do they need to coat in epoxy? Can't they just apply lots of varnish, after all isn't varnish waterproof? Is it absolutely necessary to apply epoxy and all that?

Am I missing something?

Thanks

No, varnish is not waterproof. Varnish is porous and water can go right through it, eventually. Coat for coat, varnish is only a fraction of the thickness of paint, and that is why it takes many more coats of varnish to cover for the same effectiveness of paint. In the Gougeon Brothers book on boatbuilding, they discuss the steps and techniques for varnishing for a bright wood finish. You start with two full coats of epoxy resin to seal the wood, and then you can varnish.

Eric

[michael pierzga]

Well...ive never seen a boat that is varnished below the waterline...but I can walk you to a beautiful motor launch , 30 years old , with thousands of hours spent on maintenance, that has beautifully varnished topsides !!!!

I can also show you varnished sailing dingies, kept undercover, out of the water, built of plywood and timber, who are 20 or more years old , in good condition and free of Epoxy glass coatings.

In the end you must decide on your crafts use and maintenance cycle.

If you expect to leave your craft in the water for more than the day and have generally low maintenance expectations...YOU MUST COAT WOOD WITH EPOXY.

[alan white]

There is no advantage in epoxy-coating a (varnished) boat that's built traditionally.
In fact, especially if the hull is carvel or batten-seam or even lapstrake, it is better to allow the wood to absorb water into inner and outer plank faces at (hopefully) the same rate. The reason is that while it's desirable to let the wood "take up" in order to swell the planking and seal the seams, if wood takes up on one side more quickly than the other, the planks can pull hard on their fasteners when they distort (cup) and after a number of these cycles, fasteners can no longer pull the planks back to their original positions.
As an experiment, you could take the last inch of a (1 x 6) plain board of just about any wood. Epoxy one side only and set the piece outdoors out of the sun. In no time, the board ends will go from flat to curved across the grain.
Now coat both sides of the same piece (edges too) and you'll see that the piece no longer cups (nor could such a plank swell to seal a seam).
As a third experiment, leave out in the weather a board end that has no finish on it. You'll see that just so long as neither side is being warmed by the sun more than the other, the piece is pretty stable even as it expands and contracts. Wood likes to be treated this way. It can adjust quite well to water ingress and egress if cupping is prevented. There is some strain on fasteners but overall, the worst kind of distortion is eliminated and the hull will last much longer.

[JordieS]

How do people get such a smooth finish if you apply epoxy barrier coating by a roller? do you have to wait for it to cure and then sand it down?

Thanks for your help people, you are making me ever so slightly more knowledgeable!

[hoytedow]

It is possible to get a very smooth finish using a roller followed by a brush.

[hoytedow]

See Bullet 5 of this link. As you roll it on have someone follow with a brush to smooth out the little bumps.

http://www.ftkltd.com/Topside%20Pain...%20Tipping.htm

[PAR]

I have a boat that is varnish under the LWL. In fact there's no paint what so ever, just varnish. No epoxy, no steel, no sheathings, just varnish, bronze fasteners and well fitted molded planks.

Jordie, do yourself a favor and log onto Westsystem.com and Systemthree.com and download their free user's guides. They'll explain epoxy use and techniques. The are several books that have been mentioned and wood finishing in general, is a very well covered topic here and all over the place.

As to self designing, well model making is a lovely hobby, but the ability to understand the dynamics and engineering involved is considerably more involved. For example, lets say you build a fine 1/12th scale model and it preforms to your expectations, so you figure all you have to do is scale everything up to full size right? Nope, if only it whee so easy. If you do scale it up, you'll have a boat that's way too heavy, way too short (fat) and will preform like a pig. Welcome to the wonderful world of physics. This is precisely why Langley kept falling of the end of the ship, instead of flying and when he did manage to catch enough air to create lift, it folded his scaled up ship into toothpicks.

[JordieS]

Thanks again everyone,

The model I build won't have an engine or anything in it, it will just be to look pretty somewhere around my house and if I did build a life size version of that boat I would use it only to put around at displacement speeds most of the time.