: Paul, once again I can read and learn interesting things from you.
: I suppose the square face of the "D" must be inside the
: boat, isn't it?

Yes, square face rests on the frames. For the top stringer, which would be a sheer or gunwale strip, you would probably want to make the part rounded on the top edge, too.

: And this could be useful on the multichines too, although maybe
: would be a lot of work more to save not so much weight.

If you knock off 1/4 of the wood, the part will be 25% lighter. Will that save a couple of pounds ona frame? Probably.
The big advantage would be in allowing you to use hardwoods or pine instead of cedar without paying a large weight penalty. On multichine designs you can run the chine strips through a table saw to knock off the corners, then smooth them with a few passes of a hand plane. The saw does most of the work. For producing a lot of boats you would want to use a shape, molder, or router setup to give a rounded edge to your stringers. Of course a power plane or a belt sander will do the job faster and with greater danger. Lots of ways to do this. They all make a lot of shavings or sawdust, and they all take a bit of time. How badly are you worried about weight on this?

: Would you do it on a sea tour exp 15?

Definitely. Yost bases a lot of his designs around using aluminum tubing with a 3/4" diameter. When adapting some of those designs to wood-frame construction a lot of people have gone to square or rectangular wood parts. I can't see any reason not to round off the outer edges of those wood parts (make them "D" shaped) and bring the lines back to what Yost had with his aluminum frames.

When you use square-cut lumber for your chines the fabric rubs on the two (fairly sharp) edges as well as the wide flat face of the chine. Trapped sand or dirt will slowly wear away at the fabric in these contact areas, and eventually the skin wears out. Using "D" shaped chines gives less contact area, so it should be easier to flush out debris and the skin should last a little longer. But the difference may be negligible.

PGJ