Stringer questions

Hello there,
I have learned a great deal from the expertise on this site. I am in the process of replacing the stringers on my 18 foot bowrider. I am using pressure treated plywood that is drying and will be very dry before I install it with polyester resin. I am using polyester because it is cheaper.

From all the reading that I have done, there appears to be two different ways to install the stringers, one is to raise them about 1/4 inch from the floor with foam and then glass them in, and the other is to bed them to the floor with putty or thickened resin. In both ways the stringers are not touching the floor. Which way is better?

Also, what could I use to laminate the plywood together? Would 5200 or PL Premium work? I plan to coat the stringers with resin before laminating them.

Thank you all for your help.

 

Set the stringers off the floor. I'm not a fan of filling the gap, you are still setting up a hard spot. I"glue"the ply together with a layer of mat and poly resin.

 

I bed the stringers to the hull with thickened resin (cabosil and chopped strands).
When laminating the ply together sand and prep the ply surface with acetone, coat each peace with resin and 1 layer of 1.5 oz mat, clamp and screw together so a small amount of resin squeezes out (just enough to get the air bubbles out).
After resin kicks I wait an hour or so and remove the screws and fill holes with thickened resin, I don't like leaving metal screws in the stringers. Wait for several hours before removing the clamps. After curing grind off edges, shape stringer to the hull, level top for the floor and your ready to install.

Hope this helps.

 

One more thing. does'nt matter much now if you already bought your wood but I would rather use exterior grade douglas fir or marine grade ply rather than treated. Polyester resin does'nt bond well to treated plywood.

 

Jimslade- Do you ever have a problem with leaving an air gap between the stringer and hull if you don't fill with thickened resin? It just seams like a good place for moisture to collect and have no way to escape.

 

Thank you very much for your reply.

Jimslade, you just leave an air gap, if water gets in, it will spread to the whole stringer and more problems. What about if I fill that gap with some type of foam that will prevent water from spreading and how do you create the fillet for the glass?

Itchy, you bed your stringers in, from all the research that I have done, that seems to be the most common way, not taking anything away from Jim's method, I understand that he has restored many boats and has a great deal of expertise in this area. I was just trying to figure out which way I should install them and how others have.

I will use resin to glue the plywood together as you both suggested. With regards to pressure treated plywood, I did a great deal of research on the stuff before I decided to use it. One of the benefits is that it will last much longer than untreated. Some new boat builders are even using the stuff. Based on my research, I concluded that as long as it is dry, moisture content below 18%, resin will bond to it just as good as it will bond to untreated plywood. Unfortunately it probably takes two months indoors to dry the stuff.

Thanx again for your reply.

 

I have also done tests with DRY pressure treated ply and the failure in all cases was in the ply, not the lamination. The only thing I have used in the stringer gap is foam or 3m 5200. I find that anything hard will set up a stress point that will eventually cause problems.You can make your fillets out of foam strips. Even if water gets to PT ply it will not rot for many many years. I have used PT ply and now use Nidacore. Its more work but I love the no wood aspect.I set the nidacore right on the bottom because the sides are not hard.Unless you use epoxy to glass marine ply it will come apart. Poly resin does not like the oil in the marine ply wood.

 

Thank you very much Jim,

I like the idea of bedding the plywood with 5200. It will stop any water from spreading and can use it to make fillets, without the problem of setting up stress points. I think that is the way I will go.

 

(Quote)"I have used PT ply and now use Nidacore. Its more work but I love the no wood aspect."(Quote)




I also have looked into using Nidacore. How do you like it so far? I have a few questions if you don't mind.
1. What makes it more work as opposed to wood?

2. How much more resin do you have to use?

3. What are the weight savings? I'm building performance V-hulls so wieght is a major issue.

4. Do use use it for the hull core as well or just for stringers and floor?

Thanks

 

1. You have to clear out the core, and fill with hard waterproof filler, where any bolt will be compressing on the core. 2. Same amount of resin as in a standard layup. I like to vacuum bag it but its not needed. The weight savings I have seen is around 20 to 40 percent. You can use it for the hull stringers, transom and sole. I also use it for bulkheads. I love the fact it has a shock absorber effect when impacted. I am using it in finishing off a 29 ft. magnum for the hull, stringers and transom.

 

Do you order right through Nidacore or a distributor. I have emailed them for some samples but have not gotten a response yet.

I love those old magnums. Do you have any pics of the project?


Roboj- Sorry for hijacking your thread.

 

No problem Itchy,

I am new at this stuff and it is great information. This is the first boat that I am unintentionally restoring. I did not think it would require this much work when I bought it, but it is still worth it. I am learning alot and having an excuse to be in the garage is always a good thing.

Jim,
If I were to use foam to bed the stringer, what type would I use. The 5200 idea sounded good, but it is more difficult to ensure there are no hard spots. With foam, I am pretty much guaranteed, maybe 1/4 inch foam is what I should use.

Thanx for all your help

Rob.

 

1/4 inch is fine. Here a pic of my magnum.

 

I love those classic offshore lines. What are you going to use for power?
I would like to find one to restore but they are a rare find up here in Michigan.

 

The boat was built in 1988 and was never finished.(never seen water) No stringers and the deck,console,rear engine hatch and supports needed to be trimmed,fitted and glassed in place. I bought it just as you see it in the mold cradle for 3 grand. After much thought, I am powering with a supercharged single 502. The lightweight layup and nidacore use will set the weight at about 4 thousand pounds. I hope to have it finished by next spring. I'm too busy finishing off my wifes ski boat.