How wide is the multi-chine and how stable compared to the others on your chart? It seems to have a definite advantage in terms of effort for speed but without knowing the rest it's unclear if it is at the expence of stability...

For flat water I'd say go with narrow. But keep in mind that a heavier person will sink the 15 footer deeper and I'm not sure how that affects real life speed.

I've had my Valley Rapier 18 for over a year now and on flat water and even little ripples I have no stability issues. I can paddle it in pretty much any kind of water I'd dare go out but I lose a lot of effor keeping it upright when it is bumpy even moderately. That boat is 18" waterline and quite skinny towards the ends - not a typical fat sea kayak end that is wide near the ends but a sharp shape that is thin fore and aft and wide only near and behind the seat.

Comparing that to something like a Current Designs Extreme that is both a little wider and with fatter sections towards the ends there is a clear difference - both boats go about the same under 5 mph but the Rapier just keeps going as you push where the Extreme starts "pushing water". But that's at spring speeds that help you pass someone or catch a boat wake (and stay on it easy). For just paddling under your own power for long periods - unless a very strong paddler there isn't much of an advantage IMO to something that would challenge you in the slightest wave action.

Nick Schade's Petrel is just under 20" wide waterline and about 15 feet waterline. 15' at something up to 20" wide I think is the upper limit for what you'd enjoy on flat water - longer and possibly a little skinnier will be better I think.

You can also play with swede form vs. symmetrical. Curious to see the results you get ;)

: This is hard chined Greenland style boat. 15.5 ft on the water line
: and it started at 18.5" wide at the water line.

: Then I rescaled the width of the boat to 97% and kept doing that
: with the different versions. So this is basically just a
: narrower version of the boat.

: Version 1 is Fairly stable but probably not a first timers boat at
: 92, then V2 drops to 82, V3=79 and V4= 76.

: I charted the different versions. Speed in knots is on the left.
: Lbs of resistance is along the bottom. Looking at the difference
: in resistance the gain in (potential) speed is minimal. Most of
: the gains are in the racing, real strong paddlers and sprinting
: speeds. So for less stability it appears you gain minimal
: advantage. Version 2 seems like the best compromise to me.
: BTW, the blue line is a multi-chined hull. I wanted to compare it
: too.