I don't know why Zimmerly chose the displacement he did. He probably chose a waterline and then calculated the displacement at that waterline. The water line he chose places the front jaws about 1" above the waterlevel, which reduces the chances of catching weeds.

If you wanted to have the boat float at Zimmerly's waterline and you wanted a displacement of 230 lbs you would need to increase the displacement by a factor of 1.53. You could do this by multiplying the widths by 1.53 to make a boat 26 inches wide. Or you could could multiply the height and width by the square root of 1.53 or about 1.24 to make a boat 21" wide.

To figure out your factors, decide on your displacement goal and divide by the design displacement to come up with a displacement factor. Then come up with a set of width, height and length factors which, when multiplied together equal your displacement factor. ie the width factor x height factor x length factor = displacement factor. If you want a single factor for all dimensions just take the cube root of the displacement factor.

I am not sure which design waterline will work better mine (at 215 lbs) or Zimmerly's (at 150) but by looking at the two you should get a feel for the range of displacements and their effect on the waterline.

: It's really nice of you to put these plans on the net.

: you mentioned that David Zimmerly assumed 150# displacement.
: this sounds a little wierd to me.

: why would he do such thing ?

: with such dimentions most chances are that he himself would have to
: scale it up if he wanted to build one for himself !

: I think it's wise of you to give us "the real thing" & let us
: mess it up.
: I Understand it's simple to scale it up on a spread sheet.

: Do you have an idea about the factor we should use to achieve a desired
: displacement ?

: for example: 44# boat plus 150 or 160 or ....... or 200# paddler .

: I'm not sure how complicated it is to calculate all these factors,
: but if it's not too complicated, could you post few factors for few
: displacements so one could put them on a curve & calculate whatever
: displacement he wants ?

: or if it is simple enough, could you post the equasion of that curve ?

: I am assuming the displacement isn't multiplied by the same factor
: as the offsets. Is this assumption correct ?

: I don't mean to harrass you. all the above only if it doesn't takes
: much of your time.

: thx

: Erez