Need help building long 18'+ stringers

[getusummm]

I have recored and closed in the transom of my 28' Master Marine center console and am moving on to the rest of the boat finally. Right now I am working on the stringers. I have removed 16' so far and will be cutting out the bow fishbox to see how much furthur I need to go to hit dry wood.

My question concerns the actual building of the new stringers. This is my plan as of now, unless someone gives me a better idea. The orginal stringers are 3/4" or 5/8" plywood encased in woven roven and tabbed to the hull. My plan is to use 3/8 or 1/2 plywood laminated together with the joints stagered every 4 feet, then bed the stringers to the hull using cabosil thickend resin. After that I plan to cover the entire stringer and extend the material at least 6" on each side of hull using 1808 biaxial and vinylester resin. Sound good? Or would I be better off using 3/4 plywood scarfed and glassed in?

If I go the 1/2" laminated route, do I need th scarf the joints? If so, how long of a scarf and what is the best way to scarf them?

I was told that I could just butt two pieces of 3/4 plywood together with a small scarf and then glue and screw a piece of 3/4 to the outside of the joint and then glass it all in.

I am leaning towards laminating the 3/8 or 1/2 together, but the 3/4 idea would save alot of time and materials.

Thanks for the help,
Patrick

 

[rockyrude]

Re: Need help building long 18'+ stringers

If you have the room, laminating the 1/2" staggering 4' is best. The stringers are the backbone of the boat and cannot afford to flex. I didn't have the room and ended up laminating 3 1/4" pieces using the pl, they aren't going anywhere.

 

[getusummm]

Re: Need help building long 18'+ stringers

Rockyrude, I do have the room to laminate the 1/2, which would actually give me a 1/4 more than the factory. I dont know how much strength that would add though.

Your reply does bring up an interesting question though, now that I think about it. Would 3 pieces of 1/4" laminated together be stronger than 2 pieces of 1/2?

 

[57chris]

Re: Need help building long 18'+ stringers

Would 3 pieces of 1/4" laminated together be stronger than 2 pieces of 1/2?

I would say no, I don't think the laminate pieces are any thicker in the 1/2" ply, just more of them...so 1" versus 3/4" I'd have to think 1" will be stronger.
just my 2c

 

[getusummm]

Re: Need help building long 18'+ stringers

Anyone else?

 

[sjdoo2]

Re: Need help building long 18'+ stringers

Rockyrude, I do have the room to laminate the 1/2, which would actually give me a 1/4 more than the factory. I dont know how much strength that would add though.

Your reply does bring up an interesting question though, now that I think about it. Would 3 pieces of 1/4" laminated together be stronger than 2 pieces of 1/2?

My vote is for the 3/8ths times three. It would give you 1 1/8" and you could stagger the seams.
To my defense, yes 2 1/2" pieces without seams would be stronger than 3 1/4" pieces without seams.

 

[jonesg]

Re: Need help building long 18'+ stringers

I keep reading this identical question all over the internet.

just do it.

 

[drewpster]

Re: Need help building long 18'+ stringers

I answered this question by considering how my boat was originally built. There are basically two schools of thought on the subject. One is that stringer's strength comes from the core material. The other is that its strength comes from the glass surrounding the core. Both are legitimate in my view. (It is also a possibility that the builder considered both the core and the surrounding fiberglass when building the boat.)
Since we did not engineer the original design we have too look at the way the boat was built and use our own backyard thought process.
Since the original stringers were made of ply, then it is a safe bet to use ply for your replacement stringers. (goes without saying) Since the original stringers are very long, it is safe to assume the factory had to join lengths of plywood to make up the distance. (again, it's safe to do the same) If you can see the method they used to join the ends, simply replicate it in your new stringers. If you cannot tell how the factory did it, then the method you use is going to depend on your confidence in your ability to make a strong joint. Personally, I am no carpenter, so I picked a method that I have the most confidence in. I laminated the stringers together and over lapped my joints using straight cuts. (no angles at the joint) I picked that method because I needed thickness (1 3/4) to replicate the original stringer. If the stringers were a single thickness (1/2, 3/4, 5/8 ect.) I would have butt jointed the ends and used plywood plates on either side of the joint. After that, a covering of fiberglass, at least as thick as the original, should be applied over all the new wood. Then when you are done have confidence you did it at least as good as the factory, and probably better!
The point is to use methods that you are confident in. You are probably putting more thought in to it than the original builder. You should have seen the shoddy work I peeled out of my hull! (still lasted 30 years before I tore it apart)

 

[getusummm]

Re: Need help building long 18'+ stringers

Thanks for the replys guys. I reviewed OOOPS extension project and took a close look at my orginal stringers. They were 3/4" regular plywood that was only 3 layers total. The joints were simply butted together with an extra piece of woven roven over the joints. I picked up some 3/4" plywood that is 6 layers and will lap joints like OOOPS did on his stringers. Hopefully I will at least have them built, bedded, and tabbed in the boat by tomorrow night