Timber lumber

drewpster

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Oct 17, 2006
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My little tri-hull project has three main stringers under the deck. The center stringer along the keel runs the full length from bow stern. (about 12 ft. long)
It is a single piece of lumber that was shaped and glassed into the hull. Originally I intended to replace the center stringer using plywood, built to match the stringer's shape. It would need to be 2" thick and 12' long. Given the amount of labor needed to rebuild it out of ply, would it be better to use another solid piece? I have a specialty hardwoods business here in town that can get it. If so, what kind of wood do you think this is? Birch? ( I am no wood guy)
 

Bondo

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Re: Timber lumber

Ayuh,...

Personally,... I don't think dimensional lumber has Any place in our boats,...
Plywood does the same job,.. Better...

I'd lay up a doubled 3/4" plywood keel, at 1, 1/2",... Plus your Glass....
 

redfury

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Re: Timber lumber

Drew, if you want to use dimensional lumber instead of ply, here's what you need to take into account....

The grain. If you have any grain pattern to the wood that curves, the wood will react against that change in direction. You can use it to your advantage, depending on what kind of forces you want to apply.

From what I noticed in my boat when I pulled the wood out, I think they used some type of Fir, as it generally has a straight grain and is lightweight, so grain curvatures really weren't anything to worry about.

If you need 2" in thickness, then I'd use 2 board an inch thick and then glue them together with water proof glue so you get the advantage of a plywood to a degree. Butcher block is stable because you have a lot of thin strips of wood glued together, and the best butcher block is "end grain", where you essentially have lots of little blocks of wood standing up, glued together. It's harder to crush the ends of the board, than the sides, thus the strength.

I'm pretty sure that you can get plywood in 12ft lengths though the cost obviously goes up.

On a side note from another thread, I was looking at the base weights for Glastrons when they switched over to their VEC building process ( no wood mold construction ) and the weight for a 17 ft boat went from 1350# to 1900# :eek:
 

tashasdaddy

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Re: Timber lumber

dimensional lumber has a tendency to split and twist. then ad moisture, and drying, and it gets worse. look at a 2x4 that is laid out in the weather.
 

redfury

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Re: Timber lumber

dimensional lumber has a tendency to split and twist. then ad moisture, and drying, and it gets worse. look at a 2x4 that is laid out in the weather.

Depends on the grain of the 2x4 though. I've got a couple outside. One is still straight enough to use to frame a wall with. The other might as well be made of pretzel wood.
 

Bondo

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Re: Timber lumber

Ayuh,...

And the Point Is,.... It's a Non-Issue with Plywood....
 

halas

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Re: Timber lumber

" It would need to be 2" thick and 12' long."

How wide is it?
 

mthieme

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Oct 6, 2007
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Re: Timber lumber

Plywood can rot, absorb water, have the glue fail, warp and do other weird stuff too.
There is no stress in plywood which is a plus and it is stronger 'on end'.
There is nothing wrong with using solid wood, done so on many occasions (although used plywood much more frequently).
Fir, hemlock, red oak, balsa, cedar, basswood, mahogany, teak are 'marine friendly'.
Do not use poplar, white pine,
Never tried birch, ash or maple.
I have seen cherry and interiors.

It would be ideal to remove the old stringer so as to use it as a template.
Chances are you will need a bandsaw.
 

redfury

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Re: Timber lumber

I think the only advantage to using dimensional lumber would be weight savings if using a wood like balsa or Fir. Plywood is going to be heavier per foot than a lot of dimensional lumber. And you want to make sure you are using the right kind of ply.

Realistically, you could use a resin friendly foam lay up with a wood strip on top to screw into if you were building the stringers with the fiberglass being the strength of the stringer, instead of relying on the wood to take the stress.
 

J. Mark

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Sep 3, 2008
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Re: Timber lumber

I've been fighting with myself over this very issue on my boat. Factory wood was dimensional lumber and after 20 years was at least 35 % rotted away, but mostly due to many holes and unsealed areas + additional foam being added that was not closed cell and blocked the drain holes.

I've had dimensional drying since September and have decided to use it . . . but it will get epoxy resined and wrapped and all holes will be resined and sealed properly.

If I understand things properly, the glass layup provides your strength, the wood is there to provide a form and an anchoring source for the engine mounts and the floor itself.

With properly layed glass, strength should not be an issue. If hollow stringers work, it seems to me that the choice of wood is perhaps a bit overstressed.

(taking a break from grinding glass on a vacation day-I really know how to live it up!)
 
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