: Also you can go over the displacement with this boat an
: additional 60-70lbs and only sink the boat an additional 1".

This is a good point worth thinking about. Don't make the mistake of thinking
that the design displacement is in some way a limit - on the contrary it is
just a target. With any boat, even if paddled by one person, the amount of
kit you carry is going to vary depending on the trip, so if you expect to take
80 pounds of kit on a camping trip (kayakers tend to feel able to carry more
heavy stuff than backpackers:-), but only ten pounds on day trips, you want
your design displacement to be in the middle, paddling 35 pounds under that
displacement on daytrips, but 35 pounds over on longer trips.

To give you an idea - I built a Great Auk scaled down by 5/6 of its original
size. The displacement scales as the cube of that ratio (so 125/216, which
conveniently gives a design displacement of 125 pounds), but the weight of the
boat scales more like the square (it's the boat's surface area that counts,
although I did build it a little thinner than 1/4" strips). This boat was
for my daughter (then 7) with the idea that it would be about right for her
with some gear as a child, but still about right as a dayboat assuming she
grew up to about the same weight as her mum (90-100 pounds). However, I can
paddle that boat, at which time it is displacing about 210 pounds - the
stability is not that high and the freeboard less than you'd want in rough water, but she does paddle very fast, as the frictional drag from such a
low-surface area and narrow boat is very low. So you can push way outside
the "design" conditions as long as you get the design to be about right
for your average between daytrips and camping...

Andy