MDO vs Marine Plywood?

Guys I'm surprised everyone is not all over this. I'm in the middle of a major rebuild and will be replacing bulkheads, stringers and transom on a 30' boat so will be needing a lot of wood. I've priced some marine plywood and at over $100 a sheet it's a lot of money! I've read in these forums where you can use some good external plywood but knowing that there are internal voids could lead to some problems.

Given this there looks to be a good compromise which is MDO (Medium Density Overlay) is used by the highway dept for signs and I understand lasts years in extreme weather. I checked MDO at Home Depot and it's 1/2 he cost of marine plywood, the 1/2 has 5 plys so seems to be pretty strong and by looking at the edges there doesn't seem to be any voids that I can see. It comes in 1/2"' 5/8", and 3/4" and also 1" but not sure.

So at $44 for a 4' x 8' x 1/2 MDO G2S (coated 2 sides) this seems to be a good deal for plywood that seems to be equal to marine grade plywood.

So why isn't everyone using this stuff??????

Re: MDO vs Marine Plywood?

Should do just fine, Chris Craft used a good quality MDO in many of their Sea Skiff boats over the years, above the waterline, for a long time, and it's held up just fine. As long as it's a good grade, and you seal it well, it is fine.

Commercial yards use MDO in some of their yachts and big ships, it's heavier, but also cheaper. It's less practical to use in smaller boats though, as you often have to curve the pieces, which is more difficult to do with the MDO.