: A rule of thumb that I use is that human beings can began to feel differences
: in effort when they amount to 15% of the total effort involved.

Thank you! That tidbit will go into my notebook!

One of the things that has really surprised me looking that resistance figures on my different designs is how small they are. For example my nieces boat design is taken from mine. It 2 foot shorter and I think 1" or 1.5" wider. But the differences are minimal. My boat becomes faster/lower resistance only at higher speeds exactly as I have read, where the longer length makes a difference. Resistance is higher but not very much at the lower speeds.

Just for kicks I took her boat and changed design weights and compared it with my weight and her weight in the boat. At 3 knots it's .03 lbs difference. :-) I doubt that will matter.

All in all, this has been very interesting to me.