I prefer to us okoume. It is stronger, has more plys, is smoother and takes epoxy well. It is also expensive. A more cost effective is marine meranti. This is a good structural panel. with the same number of plys and is also built to the BS 1088 standard. The surface is darker,and has a coarser grain. On the other hand , marine fir is relatively inexpensive but I have found delamination's, warping and voids.
I have built boats and boat parts with it. Good durability, nice to work with. Not as inherently durable as Sapele but also not as expensive. As with any plywood, make sure to seal the edges well with EPOXY. I always coat 100% of my pieces with West laminating resin, even if I am going to paint it.
The hull of the big boat is 1/4" Okume ply, soaked in Awlgrip two part primer and painted. The dinghy was 20 years old in the photo, 100% epoxy coated, in fine shape. I did glass the outer face of it to reduce damage from abrasion on beaches and pilings. It was like a truck for me for 20 years.
I got a better price locally from Chesapeake Light Craft than from Exotic Lumber. Exotic is much better on solid wood species.
I second the opinion on the fir; I used it to build a pram in the 80's and it did eventually delaminate and has a lot of voids. Never used Okoume, but Meranti is very nice to work with, has no voids, uses water & boil proof glues and actually finishes off bright very nicely too if you want to varnish. Built two skiffs and a lapstrake row boat with the stuff and would highly recommend it. If weight is a priority, I think Okoume is lighter, but not sure by how much.
There are two meranti marine plywoods on the market. Meranti hydro-tek is the bs 1088 standard and meranti aqua-tek is the bs 6566 standard. I've always used the aqua-tek since it is less $$$, and have never had a problem with it in the last two skiffs I've built.
The meranti boards we used a couple years ago to trim out the posts on a large screened-in porch were different than the meranti marine ply I've used. The boards are called red meranti in my Selectwood Catalogue with a note that it was formerly referred to as Philippine Mahogany. The grade is PHND (pin holes, no defects), and it did have many small pin holes in the surface. The plywood doesn't. We would occasionally see the white streaking in the wood, too.
I'm guessing you guys are not glassing over the meranti, sapele, or okoume? Just an epoxy finish? There are plenty of doug fir work boats out there with 20+ years on their hull, they just aren't as pretty or light as the beauties above.
The boats I've built with meranti (I'm just a hobbyist, not a pro boatbuilder) were all stitch and glue plywood hulls. They were all designed to be sheathed in fiberglass inside and out with several overlapping layers of glass at the critical stress areas.
Many of the non-hull parts in the cabin/pilothouse skiff I'm building now are 2 step MDO. This plywood is basically doug fir with ext glue, no voids that I've seen yet, and a paper covering on both sides. I'm using it for bulkheads where I tape the edges to the hull, lockers, bunk tops etc. It saves a lot of time finishing it compared to marine fir, but I still coat it with a couple coats of epoxy to seal it.
Building my first boat using okoume ply. I work in the woodworking industry so I am familiar w/ plywood. The stuff is unbelievable. Agree w/ everything said. There are cheaper versions from china that "says" they are to 1088 standards. Try to stick to European brands like Joubert or Bruynzeel Hechthout
you can soak the good okoume raw unfinished in a bucket of water for years.
I have heard of pieces of scrap screwed up against dock in maine for the summer. Taken off sanded and like never exposed to elements.