PLY WOOD: WHY USE MARINE IF COVERING WITH FIBERGLASS
- Thread starter ryanbabb
- Start date
Ray
Well-known member
Using "marine" fir and "marine" okoume plywood are not the same thing. Fir plywoods have voids in them just like normal plywood, but they have better water resistant glue than exterior plywood does.
British Standard marine plywoods (BS1088 stamp on them) are nearly void free.
Even when sealed with epoxy the voids will accumulate water vapor through the freeze thaw or hot cold process and will begin to rot.
All makers of guality epoxies will state that their products are not water proof. The are highly water resistant, but they do allow osmosis water transfer on the molecular level. Of course this is really small scale, but over a long period of time it can add up a major problem, which is why we here usually recommend to use the best materials you can afford.
British Standard marine plywoods (BS1088 stamp on them) are nearly void free.
Even when sealed with epoxy the voids will accumulate water vapor through the freeze thaw or hot cold process and will begin to rot.
All makers of guality epoxies will state that their products are not water proof. The are highly water resistant, but they do allow osmosis water transfer on the molecular level. Of course this is really small scale, but over a long period of time it can add up a major problem, which is why we here usually recommend to use the best materials you can afford.
Lee Harker
Well-known member
My biggest reason for using a QUALITY marine grade plywood is that it has no voids in it's cores. Voids in the core will create condisation and over time will start the plywood delaminating. Another reason is you WILL get dings and scrapes that may go through the cloth and epoxy allowing water to wet the wood...even "exterior" grade plywood can delaminate when wet and mold can grow where it's wet. Yes, there are probably thousands of boats made with the cheapest materials you can get that never had a problem and if you want to spend an inordionate amount of time fastidiously maintaining it..use what you want. A lot of damage is hidden under paint and doesn't show up till the worst time. Whatever you decide to go with, we will still be here to help.
Chris Pratt
Member
exterior grade wood is heavy. A/B exterior ply is pretty pricey and as stated has voids. The price difference between good exterior ply and marine grade ply will be only a few hundred dollars difference in the total wood cost. Spending 1500.00 on a BB3 vs 1800.00 using marine ply doesnt really make sense. Check out Noah Marine for some good prices on okoume.
Chris
Chris
I'm sure someone has but the ones I've seen built with domestic ply they've had more than their fair share of problems. I have never ever heard anyone say, "I wish I would have used cheaper materials." The converse doesn't hold.
Pete McMiller
Well-known member
I agree with everything that has been said so far and will add this: The cost of my BB3 was $2200 to $2500 when I got all done (I don't remember exactly). Included in that is the cost of a custom gas tank, all hardware, primer, paint, sandpaper, epoxy and wood. My BS1088 plywood was about $750 of the total. If I had gone to the local lumber yard for plywood I probably could have saved $4-500 or about 20% of the total. That 20% was well worth it in piece of mind alone. You absolutely won't regret using the best BS1088 marine plywood when you start working with it, it is THAT good.
Tough to add to anything said except this. Plywood is laminated wood with glue. I learned while running a tape factory years ago that the best way to "deaden" adhesive was to freeze it. When I studied Marine plys I learned that the glue used in the highest quality plys were rated to many many degrees below zero C and that clinched it for me as I like hunting in the coldest of weather. Not that any plywood out there delams because of freezing weather, but it added to my piece of mind nonetheless and sometimes that's worth a premium.
Don't skimp.
Don't skimp.
AC exterior does not hold up. A lot of the multihulls in the 60's & 70's were made from sheet AC plywood. Brown, Piver and Wharram were the main advocates. I have not seen any of them still around. Most of the good designers went to what is called double or triple diagonal planking. I have even seen mahogony doorskins used in a triple layer on a 42 foot trimaran that worked perfectly. These lasted quite well. Actually this would be a good system for building a duck boat. It will take a compound curve while plywood will not. This would allow building a deck with more camber in it than sheet ply would allow.
Gary
Gary