type of wood

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macs
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type of wood

Post by macs » Mon Mar 02, 2009 10:32 pm

What type of woods are good and bad for boat building besides ply?

Coated with epoxy:

oak, cypress, fir, etc...???



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Post by Daddy » Tue Mar 03, 2009 9:19 am

In theory, any wood (making no allowances for difference in strength), well coated and sealed in epoxy could be used. There are difference in rot resistance but if the wood is well sealed...? Probably better to stick with rot resistant wood in case of a failure in the coating.
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Post by tech_support » Tue Mar 03, 2009 10:59 am

There is a handy reference table in the Gougeon Brothers book on boat building that outlines some of the technical figures of different species.

In general you are looking for highest strength to weight, less prone to rot, availability, etc.

One you knoe the speci, then you have to find it in good quality. For example; fir might look real good technically, but you better find good pieces

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Post by macs » Tue Mar 03, 2009 7:13 pm

Thanks for the help guys. I'm building a seat with a back that swings forward or backward, like you see on a lot of center consoles now, and I'm thinking of making the uprights out of 2x4 oak or cypress.???? I plan to seal whatever I use in epoxy. I had one years ago which had uprights that were made of redwood. As I remember, we never had problems with it, but I'm afraid that it wouldn't be strong enough.

By the way, I'm building one of Jeff Spira's Carolina Dory's. I enjoy your website and have learned a lot from the tutorials and reading the forum. I was looking at the 18 dory but decided to build a ply on frame instead. I appreciate your help, this is my first. Thanks again.

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Post by tech_support » Wed Mar 04, 2009 8:44 am

For such a part, I would probably use laminated plywood covered in a light glass cloth. Its more stable, stronger, and easy to find.

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Post by TW28RJ » Wed Mar 04, 2009 12:09 pm

interesting..

There is a lot of conflicting information out there with regard to wood species and rot example: many Maine lobster boats are often made of white pine. If you believe what you read they should have all rotted and sunk within a couple of years after launch, but they don't.

Conversely you will read that if sealed in epoxy the issue of rot disapears becuase all moisture is sealed out. I would suspect that some amount of moisture would permeate the epoxy, to what level I'm not sure. (ref polyester vinylester ) I think it's time for some long term experiments with different wood types properly sealed in epoxy to sort some of this out.

Maybe 10 or so common wood type samples allowed to equalize to the same moisture content, then sealed in epoxy as in composite construction, then submerged for a year or so in h20. (there would need to be a control sampe not imersed in water) When removed after a year several tests could be performed to the control sample, bond stength, moisture content etc..

Any thoughts on wood types? I'm willing to start this in the spring.

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Post by tech_support » Wed Mar 04, 2009 12:27 pm

Conversely you will read that if sealed in epoxy the issue of rot disapears becuase all moisture is sealed out. I would suspect that some amount of moisture would permeate the epoxy, to what level I'm not sure. (ref polyester vinylester ) I think it's time for some long term experiments with different wood types properly sealed in epoxy to sort some of this out.


Its been done! Several decades ago the Geogeon Bros. tested and documented epoxies ability to encapsulate wood. This is what kicked off epoxy boat building.

Now, its very well established. The permeability of epoxy has been tested many times. The data are available many places online, most epoxy manufacturers will post this data for their products.

Epoxy has virtually has nill permeability by water. Much less than polyester or vinylester.

The permeability can be less or more depending on the type of hardened, fillers added, if its been diluted, etc.

examples:

5 minute cure epoxy is not "water proof" as are most general purpose laminating epoxies.

Adding micro-balloons for sanding makes the epoxy more easily penetrated my moister, that why you seal up fairing compound with plain epoxy or epoxy primer.

Thinning epoxy to make it "penetrate" wood will make the epoxy more penetrable by water.

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Post by TW28RJ » Wed Mar 04, 2009 1:08 pm

Then the subject of wood species in composite construction would be limited to wood strength density etc.

Don't get me wrong, I have no issues with composite construction using epoxy. (I am building the TW28) I just believe testing should be done to determime if other available wood species like poplar could be used in boat building such as cold molded construction. I don't believe Geogeon Bros addressed this, they addressed epoxies and permability. They still list age old data on suitible wood species for boat building in there books.

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Post by tech_support » Wed Mar 04, 2009 1:35 pm

TW28RJ wrote:I just believe testing should be done to determime if other available wood species like poplar could be used in boat building such as cold molded construction. I don't believe Geogeon Bros addressed this, they addressed epoxies and permability. .
True, my comments were only pertaining to the question of epoxy permeability.

If you encapsulate a piece of poplar (or another speci held to be more prone to rot) it should not behave any differently than an encapsulated piece of mahogany or locust (known for rot resistance) if kept in a relatively static environment. What may be interesting is to show is how weathering (heating/cooling) the encapsulated wood could make for little cracks that would let in moister - like what happens with fir plywood, "checking"

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Post by jacquesmm » Wed Mar 04, 2009 1:52 pm

The Gougeon test measured moisture content in an epoxy plywood laminate. They concluded that after 20+ years, the wood or plywood used in a hull coated with epoxy stabilized at a very low level. That level of moisture after 20+ years was very close to dry wood, close or equal to the moisture content of the wood before being integrated in the hull.
(If I remember well, the boat was Golden Daisy build in the 60's).
This shows that epoxy while not 100% impervious to moisture can be considered a perfect moisture barrier for all practical purpose in boat building.
The specie of wood is irrelevant to the results, they measured variations in moisture content.

I want to add two points:
1. They tested a cold molded hull. Our hulls are different. A cold molded hull has no or only a very thin layer of glass on the outside. Our hulls are a sandwich with a thick outside skin. The resistance to moisture absorption in our hulls will be much much higher because of the existence of that thick skin.
2. Wood specie: we should not only think of the fiberglass skin but of all the other possible points of entry for water like inadequately coated tru-hulls, screws and scratches in the hull for example from grounding. That is a good reason to pick a type of wood with the best possible resistance to rot. Poplar is at the bottom of the scale when it comes to moisture resistance. I personally tested Eurolite, a poplar plywood labelled "marine" on a FL12. Some parts were epoxy coated, some fiberglassed. Once the hull had a few unrepaired scratches from beaching, the plywood delaminated in less than a year.
I owned a PK78 made from very cheap Lauan and that one used the same way, with same scratches, lasted almost 10 years and only died from repeated collisions with my lawn mower . . .
Unfortunately, good quality Lauan does not exist anymore. At least not in the US.
Jacques Mertens - Designer
http://bateau.com

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