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Most of this most of you know already. I've just copied and pasted this from the notes I prepare for my students. It may help someone here.

A note on Plywood

Plywood comes in many different types from all over the world. From Domestic ply for Furniture to Exterior WBP (Water & Boil Proof) as used in the construction trade and on to Marine Ply for the Marine Industry.

Domestic Ply is usually bonded with just PVA Glue which is water soluble it has no business anywhere near a boat so we’ll quickly move on.

 A lot of amateur Boat Builders are convinced that WPB will do if you coat it in plenty of epoxy, well it is good enough if you get a good quality WPB to begin with.

Personally I never use anything but Marine Ply and the minimum standard I look for is BS1088 or its equivalent. All there is, is a few dollars in the price difference, if I wish to be using the boat in years to come or if I want to sell it on with confidence I stick with Marine Grade and it is usually the first question the prospective buyer will ask.

The problem with ply is that one veneer is about the same as the next, the real expense of ply that will last you any length of time is in the glue that is used in its manufacture and the amount of veneers per thickness. If you go to your local timber merchant and look at the edge of a 6mm/ 1/4” sheet of Marine ply the chances are you’ll count more veneers in the marine grade than you will in the WPB, this is a mark of higher quality.

Another quality to look for is voids, look down the edge of the plywood there should be no gaps or pieces of veneer missing. Voids are fine for flat panelling in houses but in boat building ply is often bent or twisted into shape, these voids then become moisture traps and weak spots.  

But what about the Glue?

The Glue that holds the plywood veneers together is what’s all important. But how do you know you’re getting good stuff?

In my practice as a Lloyd’s Qualified Surveyor I test products all the time and Plywood more than most. But the extent of the test depends on the extent of the project.

Preferably I like a long slow test. No better than to test it in the environment it will be working in. I’ll see what’s available locally and put a one or more test pieces hanging off of the pier wall at the half tide mark so it spends 6 hours in the water and 6 hours baking in the sun, over a period of months I’ll monitor how or if it degrades. But that is only reserved for pre-production or big expensive projects where there is a lot of money at stake.

But you want to build a boat now, not in a few months’ time.

Alternatively there is the fast test. I take 50mm/2” x 25mm/1” samples of what’s available locally all of the same thickness and I boil them all for at least 4 hours, dry them out thoroughly in a warm place and then boil them again, the last one to fall apart is the one I use. Any ply labelled Marine or a good WBP should survive boiling for at least the first 4 hours.

A note of warning: Not all ply is what it is labelled! I once got a piece of Ply labelled “Marine Grade” that fell apart within the first hour. This is a fraudulent but common practice. It’s easy to put a “Marine Grade” stamp on anything and charge more. Even if it’s from a reputable Ply merchant with a BS1088 stamp on it, I still test it, because Ply merchants can get conned too!

Ask your local merchant for  some test pieces, tell them what it’s for and what you plan to do, they’re usually quiet obliging and as eager to know the results as you are.

All timber merchants I have ever dealt with gave special consideration to boat builders for they knew the implications involved for selling them substandard products. An impromptu meeting for someone with a certain Davy Jones.

For aesthetic reasons you also may want to consider the surface veneers as surface veneers are often of better quality than the core veneers. Some Plywood comes in an A/A veneer which means good quality veneer on both sides but it also means it comes at a price. You can also get Marine Plywood with high quality Teak or Honduran Mahogany face veneers for yacht finishing joinery but to use this in small craft is just overkill. The Marine Plywood I usually use has an A/B veneer, one good side and the other looks like a patchwork quilt. This I don’t mind so much as I’m more concerned about the quality of the glue that holds it together. I just have a think what areas of the boat are going to be painted and what areas are going to get varnished, of course all varnished areas get the “A” side up, the “B” sides get a coat of epoxy to seal them in.

So before you parting with you hard earned cash put the kettle on sit down and have a think as to how you want your boat to look when it’s finished, paint or varnish, and where? If you’re going for paint what colour?  Keep in mind light colours attract too much dirt and can be a nightmare to keep clean, dark colours attract too much heat, the plywood expands which in turn can put stress on your taped joints.

The more thought, testing and homework you do now the more time and money you save in the long run.

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This is surely an interesting topic for all of us boat builders, amateurs and professional alike and worth analyzing it in full depth, as the longevity of the boat we build is directly related with the type of material used.  This is what it comes out when google Marine plywood.

B.S. 1088: Marine plywood manufactured from selected tropical hardwood

B.S. 4079: Plywood made for marine use and treated against attack by fungi, insects and marine borers.

B.S stays for British Standards.

Wouldn't the B.S. 4079 a better choice for boat construction?   

A timely and welcomed post. Thanks Gemini!

BS4079 is a superior ply but I'd say you'd struggle to find it in your average timber merchants. You'd have to go to a specialized marine ply merchant for something like that and trust me you will pay for it.

One thing I have noticed is with Epoxy laminating resins becoming more mainstream is the quality of plywood has demised when I ask merchants they simply state there is no demand for such expensive plywood any more.

The Pahi 63 "Spirit if Gaia" was built 20 years ago with just Douglas Fir Shuttering Ply at no great expense, and from reading the reports on the latest overhaul certain patches of exposed hardwood have suffered but the main structure of the boat and the plywood remains intact.

Buy the best, in my tiki 30 ply represent only 8% of all cost, was a WBP canadian pine

This is clearly implied, but does this apply to vacuum bagged hulls as well?

In my experience, the epoxy saturates the cell structure better, and applying glass over the final structure greatly improves even WBP ply immensely. Would it be possible to use WBP for above the waterline, especially for a double laminate?

Not saying it is a substitute for marine ply, completely

 

Only curious, as someone pointed out, the ply isn't the major expense in the end.

Gemini Dawn,  This is an extremely important article you have written.  I offer our experience to back up what you say.

We bought what we thought was top quality marine grade ply in Britain from a top timber merchant and then found that what we got was delaminating in the building shed so we had to scrap our first lower hulls and start all over.  As you might expect, I was pretty mad because the Tiki 46 lower hulls were big and a lot of work and it was a hard time ahead for us.  We got compensated but it was hard going and depressing in the extreme to have to begin again. 

As it says above "NOT ALL PLY IS WHAT IT IS LABELED".  After that awful experience we inspected our ply very carefully throughout the build.  When you are coating your ply you can look across the wetted surface and see any raised areas indicating overlaps.  When you cut your ply pieces, look at all the edges to see voids or overlaps.  All the time look to see that the glue between laminates is actually holding the laminates together.  Our first bad ply had missing glue in some places and in other places the glue had cured before the ply was pressed together because with our bad ply you could tear it apart with your fingers.  We had a real lesson in how bad ply can be and still carry the fancy sticker which meant nothing in our case.  We hope all builders will learn from our experience. 

We know that Peace is built from all good ply - top of the line marine grade ply because after our bad experience, when we started over, we inspected and inspected and inspected.  It is your boat you are building.  It is your life out on the ocean.  INSPECT and if you find some bad ply, take it back to your timber merchant and he will replace it for you and it is a good thing for him to learn about his supplier.  Epoxy on the outside cannot fix glue problems between the laminates.   

On a happier note, we are again cruising south in Peace and all is well.  Nev tells me we have sailed over 50,000 miles so far.  We will be repainting the decks in Bahamas and the topsides in Cape Cod next summer.  Even needing paint, she is still turning heads in any anchorage and serving us well.

So INSPECT YOUR PLY

Ann and Nev

Although in the UK currently, my build will be the Philippines.  Despite "Far East" marine ply being readily available in the UK, in the Philippines there are only 3 main sources of local marine ply, one of whom currently is not manufacturing/supplying.  Advice from local builders there, they say exactly the same as Nev and Ann -  do not always believe the label, inspect and even boil cycle test samples.

What is readily available is "marine plywood" from China.  Problem is, ordering is only in bulk and sustainability os not assured.  Also there can be difficulty importing in the Philippines.  If it is rubbish, would not be easy to send back either!

Hopefully, I can find a reliable supplier of a reasonable quality marine ply by next July!!

Next problem will be sourcing epoxy that is amine blush free and not awash with thinners.  At least remaining lumber is OK to source.....

Hey there Peter,
Get in touch with Boat Craft Pacific, Loganholme, Brisbane, Australia, they formulated an epoxy called bote-cote. It is 100% water proof, all solids, amine free, they have the whole range of products to complete a boat. Obviously the epoxy glue, TPRDA (timber preservative and reactive diluent agent), aqua coat top coat, cop-r-cote anti fouling, all timbers and hardwares and the best part, for me at least, any epoxy that gets on your skin will wash off with warm soap and water!
Www.boatcraft.com.au, not sure how delivery would work to the phillipines, it may be worth investigating.
Cheers,
Shaun

Noah was good for me. Pilgrim still look great after 3 years and a crossing.

Peace IV experience with copper powder in epoxy:

   We got lots of compensation when things went wrong with some paint product we bought and had to sand it all off because it was wrong. For apology, they gave us a whole lot of something called Copperbot which was copper powder in epoxy and we put several coats of the stuff on the bottom carefully following all the instructions.   It simply did not work and several friends have had that same experience.  We did sand it and we did everything carefully as per directions.  It failed as antifouling.  However, it makes an excellent barrer coat so we use ablative antifouling on top and do not fear when it gets worn in places because that copper barrier coat is right there for us.  The ablative bottom paint sticks to it just fine after a light sand.  But do not count on the copper powder in epoxy except as barrier coat.  It is heavy, costly, and does not work in our experience.

There have been different variants of the same principle regarding the epoxy/copper mix, I have no idea how Bruce put this one together however the results in Australia have been outstanding.

The literature does state that in some high pollution/nutrient conditions that it may need an ablative over coating.

Years ago when talking with the developer I asked about the life expectancy of Cop-r-cote and at that stage a timber working boat in tropical North Queensland had been using it for 10 or more years and it was still working well without an ablative coating.

I guess my point is that along with the many formulations of epoxy resins resides the offshoots of those resins and their performance records will vary widely depending circumstances.

Cheers,
Shaun

Hi Shaun

Really appreciate the information.  There are problems importing to the Philippines, but we do have a chandlery group (Broadwater Marine) that have strong links with Australia and might well be able to add Bote Cote to their list of products.  They can have more success than individuals with avoiding import problems.  None of us mind paying appropriate taxes, but it is the "extras" required to release your good that can be a problem (although there seem to be recent improvements in dealing with graft/corruption).

Best regards

Peter

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