plywood for boats

[skipper123]

I noticed on this forum green treated plywod being used and painted over with fiberglass resin. After studying, researching and building a plywood boat with the west system epoxy I was told to never enclose wet green treated plywood. The mosture inside would rot it out and blow up like press wood. I had to use dry untreated plywood and compleatly enclosed it with epoxy. My next project is going to be a restore on a fiberglass houseboat and would like to pinpoint the best plywood to use that will hold up long term.

 

[Woodonglass]

Re: plywood for boats

Welcome to iBoats!!!

Most people on iBoats use Regular Exterior Grade Plywood from HD or Lowe's. Bring it home to the shop or Garage and let it set for a week or two to make sure it acclimates and drys. Then give it a 2 coats of resin. Ather the resin cures apply another coat of resin and while it is wet apply a layer of 1708 biax cloth on both sides and the edges. wet out the cloth with more resin and let it dry. It should last 40 years. I don't know anyone that recommends using pre-treated GREEN plywood for Marine Boat use. The chemicals NEVER completely dry and they would/could interact with the epoxy or resin.

Good luck with your project

 

[Bob_VT]

Re: plywood for boats

Welcome to iboats.

Really???? Show me the links. We darn near preach exterior plywood and IF PT is used it must be dried indoors.

Exterior will hold up if sealed properly for about 20-25 years

 

[ondarvr]

Re: plywood for boats

Dried PT works fine, several Companies supply KD PT ply to the Marine industry, its considered an upgrade.

Glassing over wet PT would definitely create problems though.

 

[skipper123]

Re: plywood for boats

I just looked at this post {1962 Glastron Skiflite v142 - Basic Rebuild } looks like green marine plywood. Maybe its OK if you dont enclose the plywood ? Im a newbie and yes Ive a lot to learn about restores. I bought plans online and followed directions and built a very nice boat from scratch with the west system. I had planned to build a houseboat from scratch but after much research and calculating the cost it would be way to much money especally using epoxy resin. I figure if I buy the hull I can restore with poly with the right prep work and save a ton of money. I really loved the small boat project and cant wait to get started on the big one. This sight looks like my new resource for great info.

 

[Woodonglass]

Re: plywood for boats

Yep you are right but that don't mean it's right. Like he said he is doing it "On the Cheap" Cheap is relative. If you have to come back a year or two later and do it again, how cheap was it. I always do what mama said. If it's worth doin, it's worth doin right!!! Mama Said!!

 

[monk-monk]

Re: plywood for boats

SO, what is the correct type of plywood to use...? I was under the impression that there was a specific marine grade plywood available...Perhaps i just need to go to a reputable lumber yard staffed with folks who really know wood and ask them...

 

[ondarvr]

Re: plywood for boats

There are many types of Marine plywood with different certifications and made from different woods, there is no one type, what you use depends on the requirements of the application.

In repairing fiberglass boats the type of wood isn't quite as important because your not relying as much on the wood for strength, it functions as a durable core, not the primary source of strength.

But it?s up to the individual as to the exact type of plywood used and how much they want to spend.


Pressure treated wood does dry completely and bonding to it isn?t a problem.

 

[NSBCraig]

Re: plywood for boats

Here is a good article on plywood to check out.

http://www.jamestowndistributors.co...?docId=251&title=Plywood+Basics+-+West+System


As for PT first understand that treated ply that is made to marine applications is not the same as ply made for your home and is kiln dried.


Limitations of pressure-treated plywood
Many people ask about the value of pressure treated plywood. Often, pressure treated plywood is heavily warped. This is primarily the result of the high temperature and rapid moisture take up during processing. Some plywood delaminates during the process. In addition, some pressure treating methods incorporate water repellent materials. These materials can easily jeopardize bonding so you won't be able to glue or paint the plywood successfully. Generally speaking, pressure treated plywood may be acceptable for house projects but not for boats.

 

[ondarvr]

Re: plywood for boats

Like other types of wood, there are different types and qualities of PT too, cheap warped wood comes in all styles.

I've used the good and bad, but so far have never run into any that was treated with a water repelent product, once dry all of them have soaked up whatever coating was applied.

 

[Woodonglass]

Re: plywood for boats

As I said in my previous post, MOST of the people posting on iBoats have used Standard Exterior Grade Plywood purchased @ Lowe's or HD. They give it 1 -2 coats of resin Apply a single coat of 6 - 9 oz cloth and call it good. Utilizing good coating and fiberglassing practices and this quality of plywood should yield a boat floor that will last 20 + yrs. The glues/resins use in marine grade and exterior grade plywood is virtually the same, the major difference is in the plys themselves. Marine ply is supposed to be void of voids. No soft spots. And possibly a better grade of wood material is used. As far as water resistance, they are virtually the same. Or so the manufacturers say.

 

[Peteco]

Re: plywood for boats

Unless I need an attachment point, I'm going with foam on my whole boat in place of sheets of plywood. Should save me some weight and might save me a few bucks, since foam is cheaper than plywood (I was going to use epoxy anyway).

On the transom hard points that I'll need, I will insert a phenolic disc into the laminate the same thickness as the laminate to spread the stress. In the center of the disc I may embed an aluminum bushing, depending on the load.

I'm lucky enough that the center section of my transom is 100% glass and the outer section's core is thin (like 1/2 inch) plywood that isn't yet rotted. If I ever have to replace it I'll go with Seacast, but every other structural piece will be foam - such as side panels and the bench seat. When I rebuild the rotted bench seat at the back of the boat I'll frame it up with 1/2 inch and 1 inch foam sheeting.

 

[Woodonglass]

Re: plywood for boats

Before you get to carried away with your foam lamination ideas you might want to check out this thread. Making something STRUCTURAL out of foam is not as easy as it may appear.
http://forums.iboats.com/showthread.php?t=219986&highlight=laminating+foam

 

[Peteco]

Re: plywood for boats

Before you get to carried away with your foam lamination ideas you might want to check out this thread. Making something STRUCTURAL out of foam is not as easy as it may appear.
http://forums.iboats.com/showthread.php?t=219986&highlight=laminating+foam

You don't need to use vacuum bagging or use a fancy structural foam like Divinycell. The core foam only needs to be strong enough for the shear forces placed on it. For a small boat, unless it's for a stringer or something, the foam acts more like a form than a shear web.

The only real concern is that you need to use epoxy rather than poly.

It all depends on what you're set up for. Lots of guys would prefer to work with wood and are equipped to do it. I happen to find foam easier to work with and I can hotwire complex shapes if need be. I was planning on using epoxy anyway so I won't incur additional cost due to the resin used.

 

[ondarvr]

Re: plywood for boats

You don't need to use vacuum bagging or use a fancy structural foam like Divinycell. The core foam only needs to be strong enough for the shear forces placed on it. For a small boat, unless it's for a stringer or something, the foam acts more like a form than a shear web.

The only real concern is that you need to use epoxy rather than poly.

It all depends on what you're set up for. Lots of guys would prefer to work with wood and are equipped to do it. I happen to find foam easier to work with and I can hotwire complex shapes if need be. I was planning on using epoxy anyway so I won't incur additional cost due to the resin used.

Are you rebuilding a boat you currently have, or building one from scratch?

 

[Peteco]

Re: plywood for boats

Are you rebuilding a boat you currently have, or building one from scratch?

I am rebuilding a 1987 Ebbtide. The stringers, floor and transom are in good shape, but we tore the swim ladder off, finding that it was held on with what looked like drywall screws, so I overdrilled the holes, filled with epoxy and microfibers, redrilled and installed heavy aluminum backer plates.

I have also rewired the whole boat and installed new gauges, build a new instrument panel, interior lights, stereo, etc.

The back seat is badly rotted and the side panels are pretty torn up, so I'm rebuilding those right now too. Been taking pictures but haven't put a thread up. I'll try to do that soon.

It's an outboard but while I'm keeping the swim ladder on one side I'm going to build a platform with a 48 inch ladder on the other side of the transom, because we have a disabled person who comes to the lake with us and who would benefit from an easier way to get into the boat.

 

[gugie]

Re: plywood for boats

What about MDO?It's used for in outdoor signs is not as expensive as marine plywood but the pieces I've seen seem to be just as good as marine plywood in terms of almost no voids that I can see.
MDO satisfies the APA (American Plywood Assoc.) marine requirements and usually carries that grade from them.

 

[nowback]

Re: plywood for boats

I used 5/8 spruce plywood in my aluminum rebuild.
I got 5 sheets,,, worked my way toward the front of the boat, got to
the last sheet and found that they gave me 4 spruce and one fur.
I wish i had started with the fur it was much better quality feels more
solid to stand on and was much dryer than the spruce.
I have a feeling that the fur will out last the spruce big time.
If i ever do another rebuild like this it will be 100% fur!
just my 2 cents
matt