A Photo & Discussion Forum for Wharram Design Enthusiasts
Using a waterproof glue and labeling it as "Marine Plywood", doesn't make it so. By definition, Marine Grade Plywood not only uses WBP glue, but all the interior plies are of the same species as the face plies. The interior plies may be of a lesser grade, but will be free of voids. The only exception to this is Marine Grade Teak plywood, which may use another rot-proof wood as the core. The plywood you've been offered sounds like it's intended for interior architectural work and has a pre-applied factory finish.
I found this: http://wood28.com/en/index.php
They seem to do BS1088 marine ply and have manufacturers certificates for the wood, which is a good sign.
Eric: having built a Tangaroa 35 yrs ago with insufficient epoxy, but Brunzeel ply I can tell you that you do not need to buy a fancy marine grade ply, IF you sheathe underwater with 18 oz biaxial cloth and epoxy. The topsides (i.e. sides, not deck) ply need to be saturated with 5 or 6 coats of epoxy( no cloth)then a two component polyurethane white, without primer, , applied coat upon coat while still tacky, while sides are positioned horizontally...The deck should be done as the underwater area was. This is my experience after working in the boat trade since 1976. The interior surfaces can be given two coats of polyurethane clear in the bilges, one coat everywhere else. Fasteners should be any coated steel screw designed for exterior construction, as long as they are under epoxy. For a 40 ft Wharram figure about 100 gal epoxy (part A&B together). I am glad you have a sheltered shop; that is of very high priority. Wow, building in China - that reminds me of Bernard Moitessier!)
I wouldn't trust much in the way of certification unless there is someone that one knows who is trustworthy behind it. It is a standard, Loyds isn't wandering the world making sure ply meets the standard. All you have is a promise. Marine ply is designed to be edus painted or unpainted in water, with similar durability to solid wood, though with the panel characteristics of plywood. Since that is not how one builds boats today the standard is broadly irrelevant.
I would wonder where the red cedar and poplar are coming from. Not chinese woods to my knowledge. Though we export plenty of wood...A great deal of wood that is used in boats these days is pine (luan) but it gets called mahogany in some circles. The mahogany that gained the reputation came from SA. However since that wood is likely to be cites certified some day, and not importable or exportable after that (a problem in a boat) not having real mahogany is probably a plus. Basically people shouldn't buy boats that are part of this kind of process. I have no problem making boats out of dodgy materials, but I wouldn't buy one. Most of the boats I see for sale are " made of 1088 mahogany and WEST system epoxy) but the boards I surf have so far never had that project.