OK, so the world now knows math is not my strong suit.
thanks alot, Tim!

But you reinforce my point. There's much more board feet in timber than in boards, so mills could saw alot of bf in a hurry that way.

As far as winter goes, the sash mill I recently visited (at the top of this thread) ran year-round.... They used an "undershot" wheel. Not a large diameter wheel like a gristmill, but a long and small diameter wheel (like 16 inches). The water flowed under the wheel.

The entire thing stayed submerged and thus ice-free. The folks there said if you wanted alot of power you just built a longer wheel.

So some of these old mills could run regardless of season