Transom/floor questions on my 20

[Basketcase]

Hey all. I'm finally getting a chance to work on my old potter 20. Today I installed and tabbed in the transom with 1708 and was able to get one layer or 2408 on the transom as well. I have some questions about the floor and transom.

On the transom, I was thinking that 2 layers of 2408 would be enough but I want to be positive. I'm doing a full transom for a bracket. 2 or 3 layers of 2408?

For the floor should I use .5 or .75" marine ply? One layer of 2408 on bottom and top enough? I am using 2408 because I have a 4 foot roll about 18" in diameter that I got on craigslist for 80 bucks so I'm using it!

I'm also raising the floor a few inches. What do folks usually use to do this? I got a beautiful clear fir 2x4 for the center "stringer" and thought of getting more for the floor but the stringers are slightly wider than a 2x4. I was thinking of laminating layers of .75" marine ply, using 4 layers to get the height I want. Another option is to cut the 2x4 to the width of the stringer and use 2 of them since I'm hoping for around a 3" raise.

I love looking at all your projects and appreciate the help with mine!!

Adam

[FishStretcher]

If you can avoid it, don't use plywood. Marine, or aerospace grade or whatever. Use end grain balsa before your use ply. Use *engineered* foam first, like divinycel H80 or similar.

In fact- don't use any wood. It is the achilles heel of a fiberglass boat.

If you use epoxy, rip 2" home depot pink styrofoam into shapes and put epoxy glass over that for stringer work. They are ok hollow, but better filled with foam to protect from freezing and splitting in winter. Or better yet, but structural fiberglass square tube from McMaster or Mertons or someone like that. Cheap, too.

With end grain balsa- well you can look at the floor I sectioned. But it has ~5/16" of glass topsides. And a third of that on the bottom. And 1/2" core of balsa. Not sure- that might be 3 layers of 2408 topsides?

My 3' x 3' hatch has divinycel H80 core at 1/2". I put 2 layers of 1708 or 1808 and one layer of mat on the inner surface. I would use a layer of 1708 DBM, then 18 or 12 oz biax next time.

[Basketcase]

While I do respect the use of composites and epoxy, for this boat it is not in the budget. I have too many projects going on and the boat fund is low. I have a few sheets of marine ply left over from my last boat project and I plan to use them. There are a lot of gorgeous boats on here made from glass and plywood. Also, the boat is at least 30 years old and is made of plywoood and polyester. If I even get 20 years out of it I'll be happy.

As of now my plan is 2 layers of the 2408 on the transom. One layer underneath my 1/2" marine ply floor and one layer on top, followed by a layer or 2 of matt. Obviously there will be significant 1708 tabbing everywhere.

What I really need to do is take some pics and start a build thread. Problem is, my phone is the last thing I want to touch when my hands are in the tar and feather state.

[JohnC]

I would not be worried about using wood coring for your deck. No disrespect to Fish Stretcher, if money were not an issue you could probably make the best possible fix using wood-free construction. I just know that marine plywood has great strength to weight properties and is easy to work with; it bonds well to a variety resins and is well suited for structural deck coring. There are a lot of quality brands that still use wood and without issue because its works well. Contender uses balsa coring in the hull and Dusky uses lots of plywood everywhere. As long as it is done right (completely encapsulated) wood is a good product for the job. Just be mindful to seal it well and seal any holes that you drill after the new deck is installed.

Dave Pascoe has a great article on coring, he is pretty pro-wood, particularly balsa.

http://www.yachtsurvey.com/core_materials.htm

Good luck and post plenty of pics (when you pull the rubber gloves off!).