Check out
www.oneoceankayaks.com. I built one of his boats (kayak) but, more important, the website is a HUGE bank of info that would apply to our application. Check out some of the pics on fiberglassing and joining, scarfing, plywood strength, etc. After learning all I could from OneOcean, I feel as though I have a good handle on a (hopefully) upcoming Vacationer. Adding to my knowledge from this forum - thanks to all.
I would echo Paul and others here who said not to go cheap on plywood. My first stitch and glue boat was built with Ext grade plywood. My second was built with all BS-1088 Okuome. The first boat is less than 4 years old and I am replacing pieces (seats mainly) with BS-1088. Parts of the boat look more like they are twenty years old. The outside is ok because it has 5 layers of polyurethane over Epoxy resin but the interior is not good. I need to completely sand it down to wood and redo the epoxy coating. The new boat is less than a year old but still shines like the day I finished it although I have been sailing it a lot and trailering it around. The difference between the good stuff and the cheap stuff is remarkable. Yes the BS-1088 cost just over $100 a sheet for 1/4" (6mm) but it was well worth it.
I did note that the BS-1088 was a lot stiffer than the exterior grade. In fact I had to redesign the curve on the bow to get the ply to take the curve without kerfing it. The finish is beautiful and not dark at all, and contrasts beautifully with the 150 year old rosewood I used for trim pieces and the rudder.
Paul, Where can I get a copy of that APA document?
At APAwood.org. They have several publications and documents like; FTL-GPR-113 (Wood Handbook) that will be of interest as will "Engineered Wood Construction Guide", plus the usual updates to previous bulletins and handbooks.
I recently purchased 100 sheets of BS-1088 and BS-6566 Ocoume and Meranti in assorted thicknesses. Yep a fat check, but purchasing in this quantity gets 1/4" Ocoume BS-1088 sheets at about $60, which rivals construction and APA marine grade pricing. The total project outlay will be a fairly small fraction of the project whole.
An example is my 17' Clamming Skiff, which is all 1/2" plywood and a few dozen feet of Douglas fir solid stock. 13 sheets of 1/2" APA 1-95 will run about $650, while 13 sheets of Meranti BS-6566 (Aquatech) will be about $812. This is a 20% difference in price for the plywood, but the Aquatech is a 5 ply, while the APA 1-95 is only 3. The Aquatech is of better quality, much stronger and will be constructed to a much higher standard, meaning 10 years from now, it'll still be just fine. The BS-6566 standard is the low end of the spectrum, but sort of comparable to the higher end construction and APA marine (1-95) grades.
What does this all mean, well you could build the hull shell of this skiff with the APA 1-95 and save 162 bucks, initially, but the long term outlook for this will not be good and it'll be about 40% weaker too. When you add a 20 HP long shaft, fuel tank, remote controls, steering, paints, epoxy, sheathing and all the hardware, the total project is a $4,000 boat, so the 4% savings on the total project you made with the cheap, weaker plywood just isn't as big an issue as many think when costing out the various pieces and parts of the build.
Good points, having just completed my hull i Would like to use a higher grade of wood next rime. One thing is, depending on availability marine grade here is about 4x the price, which hurts. But i will use it if i ever do another build as i suspect its easier to finish, needs less fairing etc then cheaper woods
Anyone that's tried to fair up the standard Douglas fir construction grade plywood can tell you it's an endless battle, of which you'll never get quite right. Douglas fir hates carpenters and reveals this personality trait, as soon as you place a sander on it. The best thing to do is just surrender and coat the whole thing with fairing compound and fair that instead.
Once you work with Okoume and Meranti, you'll never go back to Douglas fir. I've used these materials on builds where only the panel seams needed attention, which is a real joy. I've never seen a fair Douglas fir build that didn't have at least a half a gallon of filler per sheet.