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The APA (American Plywood Association) has just sent me the latest update to their "Engineered Wood & Construction Guide" and after a quick glance, they've made a huge change in their rating system, which affects most of the builders here.

Previously the X rating was for grade 1 exterior applications (WBP glue), but now this rating has been divided into a few different categories. Previously a CDX or BCX sheet (what's commonly used here) from the local Lowe's/Depot was rated weather resistant, grade 1 exterior, meaning it had water proof glue and rot resistant species. It now appears the same sheet isn't as weather resistant. A CDX sheet is now rated grade 1, exposure 1, exterior.

What's this all mean? Well I suspect it's a way for plywood manufactures to save money and increase profit margins, by selling plywood that's up to the job in a house, but now no longer up to the job on a boat. You see the exposure 1 rating means it can only be used in protected areas, such as under siding, under roofing systems, etc. An exposure 1 sheet isn't rated continuous ground contact, which it previously was.



This is the new label and though it looks just like the old one, it says different stuff. In this case there's no change as it's the PS 1-09 grade, which is the marine grade marking. The stuff you get from Lowe's/Depot will have a similar mark, except it'll say group 1 (construction) exposure 1 (no weather contact) or exposure 1/exterior (limited weather contact) and a different type number (PS 2-10, etc.). Exposure 1 rated panels aren't water proof! It has to say "exterior" without the exposure 1 text anywhere on the label.

I don't have an up loadable "Exposure 1" label yet, but when I find one I post it so you know what to avoid.

This sucks . . . now I have to test new panels to see how bad they really are. The exposure 1 panel rating is specifically not rated ground contact or prolonged weather, so this is typically a bad sign. As if getting reasonable plywood was hard enough.

This lets the manufactures use a cheaper, non-water proof glue and probably lets them use junk wood inside the panel too. Hanging on a house side with vinyl siding, house wrap and other stuff covering it, the panel is acceptable, but on a boat?

I'll keep looking into this development and see what's up.

On a recent kayak project I built, I read that the "standard" quality for marine plywood was the BS-1088 rating.  Care to comment?  Was I fed a line?  I'd like to make sure I have solid panels in all plys for my Vacationer.

The BS-1088 rating is the British Standard, not the APA. The British 1088 standard is the best currently available, so your 1088 stock was good stuff. It was either Okoume or Meranti and likely some of the prettiest stuff you've ever seen (if you're new to plywood ratings). In fact I've never seen a bad sheet of BS-1088, except for some Chinese import stock a few years ago that some Australian importers where trying to pawn off as 1088. This stock took the world by storm at less then half the usual price for 1088 and a lot of folks got caught with it. The price was a "tell", but many bought it anyway and regretted it.

Plywood is easy to examine once you know what to look for, but most don't so they have to rely on the label and a quick glance at the exterior. This is a common issue, particularly if you buy a stack of plywood. What are you going to do, carefully examine each sheet? I take delivery of 50 sheet stacks and I can assure you no vendor is going to let me "un-band" a pallet of stock and spend a few minutes with each sheet.

Naturally, the best thing is to learn what to look for and how to examine a sheet. A quick glance at each edge is a good indicator of the sheet's construction, as is the "off face" repairs. Over lapping internal veneers, voids, defects in the off face, bumps or hollows in the good face, when viewed at low light angles, etc.

Thanks for the heads-up on the changes. I had pretty much given up on US ply recently and this just confirms what I think has been happening even without the label change: home-center-available ply is just not going to cut it any longer.

My sister and I are working on getting a bunch of our older projects back available and this is timely info; We'll have to include notes about the changes in materials (although we were intending to do that anyway, but this codifies the changes a bit more.)

Thanks, Paul

Would anyone have a good link to, or a simple explanation of the various grades of plywood available in Europe? I will be buying locally, here in Copenhagen, Denmark, and I would like to know what to look for. I have understood that the BS-1088 is very good, but if it happens to be available, it will also be expensive...

And, continuing on that tangent, would it make sense to modify the scantlings for the Super Skipjack if I got hold of especially fine plywood, or some lousy stuff?

Heikki,  I am not an expert on plywood but would suggest that you spend the extra to get the few sheets needed to build your boat.  When you examine your plans you will see that many areas of the boat only have 1/4" to 3/8" between you and the water.  A void in a sheet of plywood can easily reduce that thickness to 1/16".  Also these boats rely heavily on the structual quality of the materials.  A large area of delamination could adversely effect the entire structure of your boat.

Many people have built these boats with lessor grades of plywood.  There was a post about 3 weeks ago where the poster commented that his boat only lasted a couple of years because of it.  I don't expect my boat to last 100 years, that would require future generations to think it worth protecting and maintaining, but I don't want to have to scrap it in 2-3 years either.

Of all the areas where you can cut costs paying for 4-5 sheets of good plywood is not one I would suggest.  I ended up ordering my plywood from a place in California.  The stuff they had locally was American made marine grade but it was junk.  The top layers had areas where the wood was lifting and separating in feather thin areas about 2' by 3'.  The sheets were 4'x8' but some measured 8'3" and some 8'5".  The edges were ragged enough for me to question the glue layers.  These were 1/4" thick sheets that they wanted $50 each for.  I ended up paying less for each of the higher grade sheets of hydrotek, including shipping costs.  I am not suggesting you buy your ply form someplace in california just that you spend a bit of time shooping around and then buy a better grade.

Terry, metric sheets are made in several sizes, but mostly are 2500 mm x 1250 mm, which translates into 49 1/4" x 98 1/2". Actually the panels is just short of these dimensions, but I rounded to the nearest 1/8".

Aquatech (Joubert panel - BS-6566 grade, Meranti) and Hyrotech (Joubert panel - BS-1088 grade, Meranti) are usually good stuff and typically metric. Again I've never seen a bad 1088 panel, though very rarely I've seen some less then high quality Aquatech.

Meranti is good stuff. It bends fairly well, is strong, finishes very well and is pretty, though dark when clear coated. Current 1/4" pricing should be about $50 for Hydrotech and $40 for Aquatech. This is retail and without shipping. If you elect for the really good stuff, the species is usually Okoume (from Joubert or other major supplier) which is about 20% to 30% lighter in weight then Meranti. This is a huge savings if building a canoe, kayak or other craft were preformance is heavily based on weight, such as a preformance dinghy. Okoume is a very light yellowish color, typically with a touch of pink. It's not as strong, but again it's light. I love the color of Okoume, because the boat doesn't become too dark when clear coated, like Meranti does.

Expect to pay about twice what you do for Meranti for Okoume. This seems excessive, but it's really not. My RYD-14.6 performance dinghy weighs about 130 pounds with Okoume or 170 pounds with Meranti. This is a huge difference in a boat where every ounce of material has a job to do and nothing is decorative. Another example is a Greenland style of kayak design of mine, which weighs 26 pounds from Okoume, but is 34 pounds if made from Meranti. Huge difference, especially when you're carrying it on your shoulders some distance.

Sapele is another species you'll find in high quality plywood panels, but it's price is getting quite high because of the difficulty in finding it. It's highly praised stuff, strong, pretty, durable, etc.

Greetings all,

The slightly oversized metric sizing of the BS 1088 Okoume plywood panels leads to some minor changes in how you can layout the parts for cutting. First, you have to measure out the station lines from one end of the panel only. If you measure in from both ends, your parts will be 2.5 inches too big in the middle. Secondly, there is enough extra material to join the panels with scarf joints and still achieve the full length in the finished part as per the plans. Lastly, if you go with the stock butt joints, the side panels are now long enough to cover the entire side of the hull without resorting to those little triangular filler pieces at the transom as mentioned in the plans.

Paul is understating the beauty of the Okoume wood. For a long time I could not bring myself to cut it. When I finally did cut into a panel, I was surprised at how nicely it cut. Considering the cost of the entire project, the upgrade from junk-grade plywood to BS 1088 marine plywood (twice as expensive) will only increase the cost of the boat about 15 percent. So, save up your pennies and purchase the BS 1088, no matter what it costs. Life is full of little regrets. Don't let your plywood choice be among them.

Cheers,
Tom

I guess I wasn't clear on my question. Yes, I will buy fairly good Marine ply. But before I get that far, I'd like a better understanding of the various numbers. BS-1088, BS-6566, and what ever else they may label them with. I would not like to look like a total idiot when talking with the shop. Also, this being Europe, I expect mostly European style labeling, so the APA stuff mentioned earlier isn't that much concern for me.

Thanks to everyone who commented.

Wow this couldn't have happened at a worse time for me. Was going to purchase my sheet stock within the next 3 months. guess i need to move that schedule up and get whats left of the good stuff!  that or bite the bullet and buy marine grade which really puts the financial feasibility of my project right at the edge. I can order ACX locally  but marine grade  i would have to travel a good ways to get or pay ungodly shipping rates.  Is epoxy encapsulation I.E. coating all wood surfaces in epoxy a viable fix? or is there a way to make Pressure treated work? I have heard stories of fiberglass not sticking to Treated wood, but have never used it myself.