Quick question: would cabinet-grade plywood work? For the 6 4x8 1/2" & 4 4x8 3/8" & 4 4x8 1/4"? Basically the entire boat?
Found nice cabinet grade plywood that is pretty cheap ($16/sheet).
Cabinet grade plywood usually doesn't have WBP adhesives and delaminates with moisture exposure. This coupled with the fact that the outer veneer is paper thin (actually, most papers are thicker), meaning you can't sand it without wearing right through the outer layer, makes it's completely unsuitable for a boat. It's a decorative sheet, intended to dress up a cabinet or home furniture. It also has no strength, usually having a junk wood core veneers, which explains why it's cheap.
This is what I was looking at....
4 ft. x 8 ft. AraucoPly Sanded ACX Panel
Manufactured in Chile from 100% Sustainable Plantation Forests, Araucos Radiata Pine Plywood is produced under the tightest grading specifications. AraucoPly ACX grade panels allow a maximum of 6 wood repairs and 6 synthetic repairs on the face, making them suitable for a wide variety of interior and exterior applications. This panel is perfect for all of your project needs, both indoor and outdoor, and can effectively be used for shelving, soffits, furniture, cabinets, yard art and several other do-it-yourself projects.
Also found this on their (Araucoply website):
All AraucoPly panels are laid up with phenolic WBP glue which is suitable for exterior use.
The face thickness is 1/10" but how does that matter if it is presanded? Shouldn't it be good enough to lay epoxy straight on without a need to sand? Anyways, just my thoughts (not very experienced which choosing specific woods for their glues etc) so I wanted to hear what ya'll thought.
Araucoply isn't a bad product, compared to many others, though a cabinet grade isn't the choice. The ACX or BCX sheets will work, but they're not very strong and they have all the issues of construction grades. The biggest of these issues is ply count and panel construction. A 1/4" sheet will have 3 plys, a 1/10" center ply and two outer faces (one pretty, the other not so much) which are sanded to dimension, making them about a 1/16" thick, when it's all said and done, often less on the A or B face. This is done for cosmetic reasons and it greatly weakens the sheet. The outer plys (less then 1/8" total thickness) in a 3 ply sheet, carry all of the longitudinal loads, while it's cross grain stiffness is carried by a single ~1/10" ply. If there are any defects (and there will be) in the inner veneers, the sheet will crack when bent around a boat.
The APA standards are voluntary and difficult to understand if you don't have experience with them. The marine standard is PS 1-95. The Araucoply plywood you're looking at is rated PS 1-09, which is a standard exterior "siding" grade. The inner ply I mentioned above is a "D" quality veneer, which is the worst possible grade. You can use this stuff, but it's weak, prone to cracking unexpectedly, especially when bent and doesn't like moisture for very long. The glue will hold up, but the wood is so crappy on the inside it causes problems. This stuff is fine if used as a sheathing or siding on your house, where it will hang, nearly motionless for it's whole life, but on a boat that flexes, moves, cycles through wet and dry periods, there are better choices.
I'm not sure where you're located, but I have contacts all over the country. Using good quality plywood on the planking just makes a bunch of sense. It's what will keep your socks dry. Lesser grades of plywood can be used inside the boat, on the decks, cabin, cockpit, etc., but the best wood on a boat is usually the planking, for obvious reasons.
Now I can already hear the gasps and the "I built my boat from Lowe's/Depot CDX and everything is fine" remarks. In reality, I've seen many of these boats and they look like they used CDX. Lines and dents appear for no reason, across plywood panels long after assembly, the paint job is rolled and tipped with a wire brush. They're proud of it and they should be, but you have the choice now. Good plywood saves tons of work come fairing time and in resale value too.
An example is a boat I just bid on. It requires 23 sheets of various thickness plywood. I'm using BS 1088 meranti for the bottom (strength and stiffness) and BS 1088 okoume for the sides and deck (lightness). The rest of the boat is BS 6566 grade which is similar to the APA 1-95 grade. I'm buying this stuff from a commercial vendor that doesn't do business with the public, so I'm getting wholesale pricing and I'm a member of a coop that buys lumber and plywood in bulk, so we can get quantity price breaks. This aside, the plywood will cost in the neighborhood of a whopping $2,500 bucks! Ouch you say? Taken in context, I'll need about $14,000 worth of materials and gear for this build, which means the hefty plywood price is only 17% of the total project outlay. Now that number isn't so hard to swallow and I'm using the best you can get too! I am saving money by using the BS 6566 sheets inside the boat, but the hull shell is all BS 1088 Lloyd's of London certified sweet stuff. The 1/4" plywood has 5 plys, not 3 and is over twice as strong as the stuff mentioned above and about 10% lighter too.
So again, it's your choice and you can only make it once during the project, so give it some thought. Do you want the prom queen that can cook good or do you want the fat girl that you mom says will make the better wife?
I built my weekender with that ACX procuct that you mentioned, including the keel. It is everything that Paul says. Having said that, I have no complaints about it yet. I didn't encapsulate it in epoxy or anything beyond what the plan calls for. I did glass the keel as well as glue a hardwood shoe over all the end grain. However, I am serious about good paint coverage inside and out. I did so in the understanding that at my age and with diligent maintainence, she should last as long as I'm likely to be able to sail her. I don't care if anyone else gets the chance to have her.Â
I also used MDO for the 1/2 inch parts. It seems to have worked out wonderfully. I did scrape off the overlay as Paul suggested when gluing the bottom to the keel, and for the chine stringers, but nothing beyond that. Your boat may not last long enough for archeologists to find, but I bet she'll last until you are tired of sailing her.Â
AL Stead
weekender Jumping Duck
If given a choice between MDO and the PS 1-09 stock, use the MDO. It's made to the PS 1-95 standard and has uniform veneer thicknesses.