I am making a small boat. It will be wooden with a fibreglass exterior. Will normal ply be ok for this job. What do I need to do to the interior and do i need to do anything before I put the fibreglass on the exterior.
We built our day sailor out of the mid grade plywood at the local lumber yard. What I mean by mid grade is the lumber guy said he had 3 types I have no idea what he meant or actually said. When he was done with the unwanted education I said we’ll take the middle priced one.
We are ready to start our 4th summer on the lake.
All we did was tape the seams with fiberglass and prime/paint it. So far so good.
Only, only, only use Marine grade plywood. The glue will fail in the construction grade when in a boat. The extra cost will make your boat worth every buck! Fiberglass resin will be your sealer on the wood. So use plenty of it and seal all ends triple. Optional interior is to use marine grade UV grade poly-urethane and use about 5 medium coats. Dry each coat and sand in between. Never wait too long between coats. Check how-to apply instructions.
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Normal plywood would be bad for several reasons. But rather than trying to sound pedantic about plywood, I will provide you a link to a provider of marine plywoods and for our readers here on Yahoo answers a list of fine marine grade plywoods with some info about each kind.
Teak – (Tectona grandis) is considered by mariners to be the world’s most valuable and versatile hardwood. The rare beauty of teak, its rich golden brown er, decorative grain and unique properties of strength, stability and resistance to wear have made it the most demanded wood for marine use.
Mohagany – Ribbon Stripe refers to the beautiful straight grained quartered and rift sliced veneers used in this product. Typical boat applications for this panel include hulls, stringers, bulkheads, cabinets, decking and transoms. The 4′ x 10′ sheets are made with premium 1.4 mm thick face veneers.
Okoume – is also known as Gaboon (from the country of Gabon). It is light pink in color with a variable interlocked grain. The panels are normally painted or finished bright. The species has a high strength to weight ratio. Be sure to finish all exposed edges and sides.
Meranti – is a plywood that typically comes from Malaysia. This plywood is in my opinion the lowest grade of marine plywood to get. You still can have gaps in between the layers of plywood, which can be a potential breeding ground for wood rotting bacteria.
Here is one of many marine plywood providers: http://www.marine-plywood.us/
Also, if you wish to go the extra mile in preserving your plywood and stringers, you can give them 2 coats of boiled, linseed oil and 1 coat of kerosene before you encapsulate the wood with epoxy resin (or paint). Putting indoor/outdoor carpet is an economical way to make being barefoot in your boat more enjoyable. If you decide to glue some carpet down, then be sure to use epoxy resin to coat at least the topdside of the deck. Don’t forget to treat the edges!
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http://www.marine-plywood.us/ , and 7 years of boat building experience. I am also a composite pontoon, boat builder. http://www.aquacub.com
I’m not an expert on this, but I have used treated 3/4 ply doubled up for transit replacement twice. Both are still working well after many years. Be advised that the brown treated ply I believe is a much better grade than the green. Talk to the wood people (lumber yard), and maybe a ship yard that repairs some of the larger and older boats. There are several close to the great lakes. Marine ply is also very heavy, hard to cut, and not much fun to work with, but most likely the best choice.
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We built our day sailor out of the mid grade plywood at the local lumber yard. What I mean by mid grade is the lumber guy said he had 3 types I have no idea what he meant or actually said. When he was done with the unwanted education I said we’ll take the middle priced one.
We are ready to start our 4th summer on the lake.
All we did was tape the seams with fiberglass and prime/paint it. So far so good.
References :
Normal ply will be okay as long as it has a marine grade "A" bond (the bond that holds the ply veneers together – "A" bond will not break down under hot, cold or wet conditions), this is the most important ingredient. People often confuse marine plywood as some magical product that is water and weatherproof- not so. Plywood is still timber and timber must be protected against the weather, for example our houses are usually given 2 or 3 coats of paint, (1) to look pretty and (2) to protect the timber against the weather.
With regard to the face grade of the ply you should look to use B or C grade (A grade is very expensive – grades are determined by the number and size of filled or unfilled knots and splits in the face, A grade has very few and small filled or solid knots and the surface has been sanded, B and C allow for larger knots and splits in increasing numbers, D grade has unfilled knots and splits and the surface is unsanded).
By using a B or C grade face you will provide a better surface to apply the fibreglass to. If the back off the ply sheet is not going to be seen you can probably go with a C or D grade. There are a variety of timber plys available as mentioned in a previous answer but plantation pine is also a nice "green" option.
Use a ply made to the Australian standard and with a stress grade rating of at least F14.
It wouldn’t hurt to have the ply treated to a H5 marine hazard level but if you fibreglass it correctly and give the back of the ply a couple of coats of a good sealer you can probably use a H3 hazard level treatment – ACQ and Tanelith E are popular types.
You can find information about plywood and Australian ply producers from Boral Hancock Plywood, Austral plywoods, Big River Timbers, Browns plywoods.
Finally go to a plywood or panel specialist as you will probably get much better prices than your local hardware store.
Remember ply that uses an "A" grade Marine bond.
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