: I happened to see an old rowing skiff upside down by the river, that was made
: of wood. The bottom was full-rounded, semi-circular in section.

That is typical of rowing "shells". The semi- circular shape gives the least wetted area for the displacement.
If it is not a true semicircle, but a bit wider, or narrower -- let's call it a semi-oval -- then you get better stability, or at least some more contol overstability, as the geometry of the boat changes when it it tipped to either side.

: I don't believe it was plywood that could be bent so hard without cracking.

Special plywoods are made for extreme bending. These typically have all, or most, of their plies arranges so th grain is running in the same direction. Depending on how you want your panel to bend you buy it with the grain running the long way of the panel, or the short way. It seems to be a popular material with cabinet makers.

Of course you can always make your own by laminating as many sheets of veneer as you need to make up the thickness you desire. Cold molded and hot molded plywood has been made for years n such a fashion. The plywood chair seats of the 1960's were one popular item. Currently you'll see this type of construction used in the manufacture of skateboards.

Clark-Craft (www.clarkcraft.com) has plans for a cold-molded "plywood" kayak. I believe you use wide strips of veneer laid over a skeleton of forms ( much like building a stripper) By orienting the strips and gluing one layer to another you achieve a solid "plywood" hull

: Though it is strange that apparently nobody builds out of covering panels
: that could be bent to shape.

Oh, they still do build with this stuff. It is just outrageously expensive. There was a link a while ago on this board to a company that builds racing shells from oldgrowth cedar. Each hull is a single piece, which they draw from a dwindling stock of thin (1/4 inch) wide (about 24 inches wide, I think) and long (20 + feet) close-gained cedar.

: Hold your flames a second, gents: I admit round-bottomed skiffs are unsteady
: and require a skeg or a rudder. That's another question, recently debated
: on the design board.

That may be overgeneralized. Round, as in circular, bottoms might need something, but rounded, (as in very soft chine or chineless) hull may or may not need skegs/rudders. A lot depends on the underwater geometry as a whole, not just how much the wood has been smoothed.

: Couldn't we "hog" or flatten such a round-shaped bottom by the way?
: I admit it would bend along wrong lines at times, that more stringers would
: be needed...though I did not see many on those skiffs, rather bulkheads
: like on our yaks.

Flattening a rounded bottom, or giving it a vee shape is common in open canoes. The flatter bottoms give less draft for their displacement and are nice on shallow water. "Hogging" by the way has a technical definition in the canoeist's dictionary, which is different that your use of the term. It is the equivalent of negative rocker, or a case where the ends of the boat are deeper in the water than the middle. Think about an aluminum canoe getting hung up in the middle on a submerged rock, or tree trunk in a river, and having the frustrated canoeists jump up and down at each end, and you can imagine how some canoes get wrecked by being "hogged".

You don't need many stringers when you have the hull made from one piece of wood. The stringers are frequently used as chines, or cornerbracing when smaller pieces or panels need to be joined. The interior chines provide a gluing area, or a surface that the panels can be attached to with nails or screws. The birchbark canoes did not use stringers a lot. Their longitudinal strength came from the gunwales, and the ribs and thwarts provided the necessary bracing to resist water pressure. Strippers, likewise do not need chines or stringers, though some designs use them for ease in attahing the deck to the hull. The monocoque hull created from all those closely fitted strips amounts to a rounded, self-bracing, shape -- and the fiberglass which sandwiches the wood provides even more strength and reinforcement.

PGJ