Having made the decision to stay with Tammie Norrie (see other posts), economy dictates it's worth trying to find the best value ply. Having looked at a few other forums (fora?), I'm aware I could be opening a right can of worms.
Obviously, there's Robbin's and their well renown products - I used 4mm for the Humble Bee mentioned before - and was looking at using their 8mm to build a nice sturdy boat, it's specified 6 - 8mm.
At £62/sheet plus delivery it's really not a cheap start and have been looking around at cheaper alternatives.
I've seen the good WBP is better than bad marine ply argument etc., etc.. but this seems a spurious argument when inexperienced at looking at ply, even when you've been told what to look for.
It also seems that BS1088 is fairly meaningless these days.
So what am I trying to say -
well, there seems to be an obsession with using 5 ply not 3 ply 6mm - what difference do the extra two plies make?
I live in N Surrey, does anyone have experience of the ply outlets around here. I have found a place called Richard Russell who supply only sheet materials includng 6mm and 9mm - anybody used them?
If not, any other ideas - I was thinking that using 9mm for the first two (bottom) planks on each side with rest being 6mm 3ply might be a good idea.
I recently used 6mm BS1088 Marine Ply from Jewsons. Quality seemed much better than the more expensive exterior grade stuff available locally and the price was much lower, about £20 a sheet, though I did have to cross the English Channel to collect it from Kent.
It is 5 ply and though i can't prove it makes any difference, it looks stronger and inspires more confidence. It cuts better, too.
What you really want is even thickness of laminations, the more the better.
With poorer quality the face plys are often the thickness of brown paper and the filling in the middle is like balsa wood, I know, I bought that ply.
5ply will be stronger than 3ply as it has more glue lines, and three laminations going long ways, two across the sheet. 3ply only has two going length ways and one across.
Ask to choose your sheets yourself and check for voids. Look along the edge of the sheet for little rectangular holes which indicate a break in the lamination which will probably go right through the sheet and weaken it. Reject any with voids.
If you have WBP grade with 5plys and no voids you've pretty much got Marine ply.
Use the dimensions Iain O gives, he knows what he's talking about.