Using cheaper construction plywood instead of Marine plywood

Spot on. There's a lumber yard near where I live selling supposed BS1088 grade marine ply. The stuff is utter rubbish - 2 thin face veneers and a single thick core in 9mm ply. I wouldn't use it even if it was free.

Compare with an Australian certified exterior grade - far better quality and ply count. The BC grade is what I'm using in the interior of my boat as it'll all be painted.

Now if I were building a hull from ply, I'd be using the absolute best stuff I could get in certified marine grade, from a known good supplier. The extra cost pales into insignificance compared to the time you sink into the build, multiplied by maybe 5 for the time it would take to fix problems from cheap stuff later.

FWIW I bought 16 sheets of cheap non-structural 10mm film faced ply to lay out the lines of my boat. I've had scraps in the weather for 4 years now just to see what happens. The glue bond is still good. Pity about the rot resistance though. However it's great plywood for lining the shed.

PDW

 

Greetings,

Found Noah's to have best prices for bs6566 & bs1088, think the 3/8 (9mm) is around $40.00.

 

I found 1/2" Olympic Signal MDO at Harbor Sales for about 60 bucks a sheet, if I ordered the eight I want to start with (so I have a surface for lofting that can be incorporated into the boat later). Unfortunately they're located back east, and I suspect the shipping would kill me. So I called the major lumber yard down the road and asked them for a quote; waiting on a return call because they don't normally stock it.

By all accounts, Olympic's Signal MDO is pretty good stuff. Their website claims they stopped producing marine fir plywood when they came up with the Signal MDO, because it's better.

 

???That doesn't make any sense. If it were better that Marine Grade wouldn't they be able to sell it as marine grade? "Marine Grade" is not a brand name, it's a quality standard. It is a fairly stringent set of requirements set out by engineers so that shady types can't fool around with vague terminology and sell us something with traits that are detrimental to our trade. When a seller talks like that it definitely turns my BS detector up to 10.

 

Why would they label it 'marine grade plywood' when it's MDO, and supposedly better for signs (its original purpose) than marine grade fir?

I've been trying to think back.... it may have been a supplier who said they stopped carrying marine-grade fir because the Signal MDO was better, rather than Olympic saying they stopped making it. I'd have to go looking to be sure, but that does make more sense.

 

My ********OMETER goes off when 'Marine' is mentioned. I immediately check to see if my billfold is still in my pocket. If it's in my back pocket, I put it in my front one.

 

Is not the boil test a good measure of the relative strength and quality of the wood? From what I have heard it seems to be a fairly important test to undertake, perhaps even with Marine grade wood as well...

 

In the USA both MDO and marine grades are built to the same standard, with the exception MDO has resin saturated, paper faces on one or both sides.

 

Thanks, PAR!