Plywood with joint vs. dimensional without

[aborgman]

So, after tearing away at the floor some more - it looks like I'm going to be putting in new stringers also. The current stringers are dimensional, 1"x4" (or possibly 6") - the longest just under 12'.

I can replace these with 3/4" PT plywood, but it will have a joint.

Or I can replace with 1"x4/6" dimensional Douglas fir, with no joint as I can get 14' lengths.

Which is preferable?

--
Aaron

 

[tashasdaddy]

Re: Plywood with joint vs. dimensional without

you splice you ply, with a 4 foot sister on each side. 2 feet each way from the splice.

 

[aborgman]

Re: Plywood with joint vs. dimensional without

you splice you ply, with a 4 foot sister on each side. 2 feet each way from the splice.

I'm not quite sure what you mean... that would make the stringer 2 1/4" wide (3x3/4") for the four feet around the splice.

I was thinking you could just use a half lap splice joint, or possibly a tabled splice joint with a good 12" of overlap in the joint and just glass it on the outside.

--
Aaron

 

[tashasdaddy]

Re: Plywood with joint vs. dimensional without

sister, means you use a butt joint with the stringer, then sandwich the joint with a full width piece on each side. using a 4 ft length on each side, with the center of the sister boards at the stringer joint. this way you have sandwich 2 feet on each side on of the splice.

 

[aborgman]

Re: Plywood with joint vs. dimensional without

sister, means you use a butt joint with the stringer, then sandwich the joint with a full width piece on each side. using a 4 ft length on each side, with the center of the sister boards at the stringer joint. this way you have sandwich 2 feet on each side on of the splice.

Pretty much what I thought - that would make the stringer 2 1/4" wide (3x3/4") for the four feet around the splice. Seems a bit overkill to me - I think if you just throw a half lap splice joint with 12" of overlap on there, along with it being plywood, it's going to be stronger than the original dimensional lumber.

--
Aaron

 

[Chris1956]

Re: Plywood with joint vs. dimensional without

Aaron, I consider dimentional lumber to be superior to plywood for stringers. If any water gets to the plywood, it will delaminate and the boat will have no strength. I would use seamless solid pressure treated lumber. Dry it well and cut it to size and glass it in. Poly resin is probably OK to use in this application, provided the surface you are glassing is solid and dry. Cover all sides of the stringer with polyester resin to make it as waterproof as possible. As long as the lumber is dry the resin will stick well.

 

[oops!]

Re: Plywood with joint vs. dimensional without

tds answer....... is fast, easy, and strong.

the lap joint process is described with pics in the hull extension thread.

if you use the lap joint....wrap the stringers in glass......(wrapping with glass is suggested any how)

 

[tashasdaddy]

Re: Plywood with joint vs. dimensional without

Chris, pressure treated lumber is known to warp, as it dries. trying to get a piece dry enough for resin to stick, and be straight is almost impossible.

this knowledge comes for many years of working with wood in the construction field. exterior, or marine grade ply is much better and easier to work with. the pressure treated wood today is treated with a compound that also eats metal fasteners.

 

[oops!]

Re: Plywood with joint vs. dimensional without

Chris, pressure treated lumber is known to warp, as it dries. trying to get a piece dry enough for resin to stick, and be straight is almost impossible.

if you have not allready dryed your pressure treated wood...and dryed it straight.....dont use it.....td is totally correct.....resin wont stick to it unless its totally dry...(bone dry....that takes over a month.....all the while being weighted down so it doesnt warp....and it will)

the ext grade is just fine....

 

[aborgman]

Re: Plywood with joint vs. dimensional without

the lap joint process is described with pics in the hull extension thread.

Yikes... I'd use WAY more overlap than that - that is 5" overlap on a 20" high board, I'm talking 12+" overlap on a 4" board.

if you use the lap joint....wrap the stringers in glass......(wrapping with glass is suggested any how)

I planned on wrapping the stringers in glass no matter what.

--
Aaron

 

[tashasdaddy]

Re: Plywood with joint vs. dimensional without

i gave you the correct way to sister a stringer, you want 24 inches each way from the joint. then glass it in.