Exterior Grade Plywood

[Mostly Harmless]

So I am just about up to the point in my project of installing the actual floor boards. I have rebuilt the stringers, foamed them in, and have two out of three floor boards cut and mocked into place. The third floor board is very tricky because it sits in the front of the hull and follows the V of the hull which is unlike the other two boards that rest on a platform where the V meets the sides....anyway, for this project I have been using the best materials I can find which includes marine grade plywood that is 13 ply thick and is the nicest wood I have seen, while using the old front floor board to help mark out the new front board I notice a very curious marking on the under side of the wood:

Apparently back in 1974 they used exterior grade plywood instead of marine grade plywood. I find this rather funny because I originally thought it was marine grade and tried to follow what the manufacture did. So now I will have a slightly heavier boat (I believe the marine grade is heavier then the exterior grade, I just don't know how much). But now it should be better then the original.

 

[BigBoatinOkie]

Re: Exterior Grade Plywood

I believe lots of folks on iboats use exterior grade ply instead of marine grade, including me. I've heard some say that the if you're glassing over the wood or coating it with resin, the chemical they treat the marine wood with could cause adhesion problems. I've heard others say to absolutely use marine grade. So I guess both of them have been used with success plenty. I used ACX since it's cheaper but uses exterior grade glue between the plys, and I coated it all over with epoxy resin and the topside is fiberglassed over. By the time i'm done glassing it, it'll be pretty dang heavy.My deck is still under construction, so who knows how it'll hold up once it gets wet. Good luck with the rest of your resto.

 

[Shife]

Re: Exterior Grade Plywood

My boat is a '87 and it was originally built with ACX.

 

[Bob_VT]

Re: Exterior Grade Plywood

Marine grade has no voids. I do know that starcraft used A-C on the decking.

 

[jspano]

Re: Exterior Grade Plywood

anything with the "M" word is costly and sometimes is neccesary like an alternater on a inboard, but wood if properly coated can be subed for marine

 

[wallybme]

Re: Exterior Grade Plywood

Marine grade has no voids. I do know that starcraft used A-C on the decking.
Not really. Some has voids while others may not. The price, however is higher for those without the voids. Another thing is that one of the main differences with the marine plys is that the glue that is used to bind the veneers are much stronger than the outdoor plys. I have a 78 glastron and a 90 Maxum. The glastron is fitted with marine ply and the deck is still solid. The Maxum has what seems to me to be outdoor ply and I have to replace the deck.

 

[jspano]

Re: Exterior Grade Plywood

The Maxum has what seems to me to be outdoor ply and I have to replace the deck

was that ply coated or glassed... i bet not

 

[wallybme]

Re: Exterior Grade Plywood

it was not coated except for about 3" away from the seat foundation.

This is what it looks like

 

[oops!]

Re: Exterior Grade Plywood

just goes to show you....even bare wood will last a long time.......we as backyard boys tend to over build.....but this is good....we just cant over do over building or we will have a submersable that aint water tight....(but the stringers and deck will be ok with 87 layers of epoxy ! LOL )

BTW....if you can pull a template off the old wood ....do it...

if you cant.....measure from the center out...

use the center line of the hull.....it will make the peice fit better....

in pro building....everything is measured from the centerline.....

 

[Mostly Harmless]

Re: Exterior Grade Plywood

just goes to show you....even bare wood will last a long time.......we as backyard boys tend to over build.....but this is good....we just cant over do over building or we will have a submersable that aint water tight....(but the stringers and deck will be ok with 87 layers of epoxy ! LOL )

BTW....if you can pull a template off the old wood ....do it...

if you cant.....measure from the center out...

use the center line of the hull.....it will make the peice fit better....

in pro building....everything is measured from the centerline.....

I definitely agree with the "backyard boys tend to over build"! Even though I am using marine grade plywood for my project I still coated it with epoxy to ensure longevitiy. My only concern now is the extra weight that the marine grade plywood adds even though I have a brand new ETEC powering the old girl.

 

[Bob_VT]

Re: Exterior Grade Plywood

The weight differences are really not that significant...... are you racing that boat?? It's a pleasure boat!

 

[ezmobee]

Re: Exterior Grade Plywood

I've heard some say that the if you're glassing over the wood or coating it with resin, the chemical they treat the marine wood with could cause adhesion problems.

I think this is PT you're thinking of. Contrary to popular belief, marine ply is not treated against rot. As was explained earlier, it's just better quality glue and fewer voids.

I was impressed with the quality of the Arauco ply from Lowes. I think I read on here from someone that it may be made from a softer wood than regular exterior grade but it sure is nice stuff and was vearly void free.

 

[Mostly Harmless]

Re: Exterior Grade Plywood

The weight differences are really not that significant...... are you racing that boat?? It's a pleasure boat!

Yes I plan on entering this years offshore powerboat racing series, I think I have an edge on those turbine power catamarans , but all kidding aside at 1100lbs for just the hull I think she could benefit from a little weight, might help to improve the ride, but considering the condition of the old floor/stringers, anything at this point will help improve the ride. The biggest set back to this project right now is NY weather.

Slightly off topic...did anyone else have to deal with the boat being out of alignment? We notice a slight twist to the hull and fixed it while we putting the stringers back in. Considering the stringers and floor were pretty beat up I am lead to believe that this happen because this items weren't structurally supporting the hull as well as they should.

 

[BigBoatinOkie]

Re: Exterior Grade Plywood

I think this is PT you're thinking of. Contrary to popular belief, marine ply is not treated against rot. As was explained earlier, it's just better quality glue and fewer voids.

My apologies. I thought marine wood was pressure treated. Shows what I know Sorry.

 

[ezmobee]

Re: Exterior Grade Plywood

No problem at all! A lot of people (including me at first) definitely confuse the two or at least think marine is treated in some way.