Re: Stringers
in the early years....the mfgr's used what ever they could...(old pallet wood)...and they proved...just about anything would work
today, the reason plywood is used for stringers on boats is because dimentional lumber is weaker,,!!!
thats right...plywood on edge is far stronger than dimentional lumber.
it is because when they make the plywood...the lay one grain going one way...then reverse it for the next....so its cross grained...
as for choices between plywood.....
marine plywood is great....however very expencive....and the benefit you get from it is so little it wont be noticed in a standard 14-25 foot runabout.
(marine ply is best used on hulls for wooden boat building)
the uasual big controversy is between pressure treated and standard ext grade plywood.
the pressure treated can be soaked in water for 40 years and not rot.....so boat builders theroy's are to use it for stringers.......
there are a few down falls to this........pressure treated comes wet....too wet and wont bond with resin unless its dry.....soooo....you have to dry it flat for a good month or so before you use it....and ...it warps when drying...so its also a real pita.....it also cannot be used with any aluminum...none at all. and you need to use special screws.
exterior grade plywood is cheap......the glue is waterproof....and it works just fine......you still need to dry it....but that can uasually be done by placing a heater and a fan on it for a week or two (depending on relitive humidity of your room)
the truth is........it doesnt matter that much what kind of plywood you use....marine..pt...or ext grade because once you wrap fiberglass around it....(an average job by an average joe).....the wood will last for 20-25 years....(much longer than you will own the boat).
between all grades and pt.....again once encapsulated....it is protected....will the pt last longer????....we dont know.....we havent had a boat that was done with pt 60 years ago to find out !
i hope this explanation helps
cheers
oops
