Marine ply question

[chrishayes]

I have the ability to get marine grade ply for 50 dollars a sheet. it is 2x as expensive as cdx. is it worth it? In the end I would think it would be cheaper due to not needing as much resin and glass to waterproof, right? I have also heard that when using it, it isnt necesarry to coat the bottom of the deck in resin, is this true?

 

[proshadetree]

Re: Marine ply question

I used exterior on mine Even if it had been marine I would have coated it.Maine reason I didnt pop for marine.I have a 75 sidewinder that has sat outside for over 10 years that had a standard plywood floor put in it you can jump on.Fiberglassed both sides and good airflow under it.Let your budget and your length of time you want to keep boat going be your guide.Lots of different views on this subject.

 

[IrishBeo]

Re: Marine ply question

I have been looking to have this question answered as well. The flooring is solid but the side board could stand to be replaced.

Ty for the advise here.

 

[Mark42]

Re: Marine ply question

I have the ability to get marine grade ply for 50 dollars a sheet. it is 2x as expensive as cdx. is it worth it? In the end I would think it would be cheaper due to not needing as much resin and glass to waterproof, right? I have also heard that when using it, it isnt necesarry to coat the bottom of the deck in resin, is this true?

Unless its CCA Treated Marine Grade, then it will rot like regular plywood. So yes, you need to seal it with resin to make it water proof, just like any regular plywood. If you want rot resistance, look at pressure treated ply. Its what the Engineered Wood Association (APA) recommends for boat building.

 

[sschefer]

Re: Marine ply question

I have the ability to get marine grade ply for 50 dollars a sheet. it is 2x as expensive as cdx. is it worth it? In the end I would think it would be cheaper due to not needing as much resin and glass to waterproof, right? I have also heard that when using it, it isnt necesarry to coat the bottom of the deck in resin, is this true?

1. Is it worth it.. Depends, if its for a transom then yes, if it's for a deck maybe.
2. Less expensive because of less resin.. Standard Marine grade plywood is just fir ply that has minor to no voids making it stronger. It is not made with waterproof glue, it's just like exterior in that it is made with water resistant glue.

3. If the plan is to use it on a deck and you were thinking of using 3/4 because of the potential for large occupants then with marine ply you could still use 1/2" and you won't have to adjust for that extra 1/4" when you start putting things back together. This alone could be the best arugument for using marine ply.

If you're looking to get out of all that glass work you won't by using marine ply. You need to step up even further and go to SuperPly from Roseburg Lumber Mills. It is supposed to be made from clear sheets of veneer and is assembled with resin glue that is 100% waterproof. 3/4" will run you 130 - 150 a sheet and you'll need to special order it.

Even then you still should coat it with at lease a Spar rated 1 part polyurethane finish.

Discalimer: This aint gospel, everybody seems to have different results and opinions on the subject. This is my two cents and based on my own experiences.

 

[chrishayes]

Re: Marine ply question

nope, just checking to see if this marine ply debate held any water! cough cough. I by no means am looking to get out of work...just seeing if spending a few hundred dollars more would be better for the boat. This is probably similar to the epoxy vs poly debate. I would like to see a good 10 years of use out of this boat. I believe I will go with CDX and poly both sides with sheets of cloth. same with the stringers. I would think using the ply doubled up on end would be a good choice due to there not being a lot offered for dimensional lumber in this height(12-14"). No matter what I do it will be better than the PO's attempt at a resto, non coated pressure treated ply and some scabbed together 2x4's to hide the fact that the stringers were completely rotted away...then a nice covering of home depot grey outdoor carpet glued on with liquid nails! Ohhhh what did I get myself into????????

 

[sschefer]

Re: Marine ply question

LOL, The majority of boat owners just want to use the boat as much as possible and when it finally wears out they buy a new one. That's the way the majority of our present society thinks things should go. Sounds like yours and most of ours were budget stretchers at some point.

I don't know if I can critcize that since few have the time, patience or money to pull off what we do with our boats. I know for a fact that I could have bought a much nicer used boat and been in the water by now for what I've spent on my resto. In the long run I win though because it's mine, all mine. That's something that few boat owners can claim.

 

[fishrdan]

Re: Marine ply question

Marine ply is stronger since the plies are laid as 45*, compared to 90* in normal plywood. Also, it's "virtually" void free, yes there are small voids in it as I found out. Could have been cheap marine ply though

You have to figure out if you need the strength of marine ply, or if exterior ply will work for your application. I opted for marine plywood in my aluminum boat since the fuel tank panel is big (30"x60") with little support underneath and the edges of the decks are not supported where they meet the hull,,, about 9-12" of deck hanging off the stringers.

Sounds like you are working on a glass hull and I don't see the need for marine ply if it's sealed up well.

 

[chrishayes]

Re: Marine ply question

thanks for all the input. Indeed I am working on a glass hull. I would like to put a tank under the deck as well but I am concerned that I dont know what I am doing enough to try it. I imagine that the hoses have to penetrate at some point and i havent a clue as to how to seal that penetration up. I am also concerned that if something were to go wrong with the fuel tank, that I would not be able to access it. What do you do then?

 

[PiratePast40]

Re: Marine ply question

Here's a link to a marine ply manufacturers web site:http://www.greenwoodproducts.com/xlpanels.htm 3/4" is only $60 a sheet. I'm sure there are other manufacturers and other methods of preservation but at least this gives you have a little more information.