: Thank you all ...and sorry for this silly question: I guess MDO is
: not MDF neither OSB. So what's the difference?
: I just know MDO means "medium density overlay"; MDF
: "medium density fiberboard" and OSB "Oriented
: strand board". Are they all good to build 1/2 sections?

No. Normally I wouldn't use any of them for frames on a SOF baots. The MDO is basically covered with paper. Great for printing signs, but it doesn't appeal to me for somthing that will be wet. MDF would be a bit more durable, but again, the fiberboard will swell when wet, and won't shrink back to the old size when it dries. If this is all you have then go with it, but seal it well with epoxy, and don't grouse about the weight.

OSB is strong and would probably work, but it seems pretty flexible for its size. I'd use a piece of 1x1 solid wood t stiffen it on the larger frames if i needed to. It looks ugly, but that can be covered with paint. One side is rough. Tat side goes toward the ends, and that is the side you glue nd screw the stiffeners to , so from the cockpit all you see are the smooth, nicely painted sides of the frames.

Plywood is simpler and faster to cut and finish. The other options will take more time. If you are trying to save money on building a lot of boats, say for a Boy Scout troop, build one with the meterial as a test before you commit to all of the projects.

Just my thoughts here.

PGJ