: Using Toni V's Freeship 'Iggy' model, I ran KAPER numbers on the hull in its
: original configuration and scaled up to make the waterline length 2'
: longer. No changes were made to other hull dimensions, and displacement
: was the same for both hulls.

Ok, I'll continue some here as the previous post was lost...

That's not a fair comparison you are doing there. If you just scale the design longer or shorter displacement will change at same waterline. So you'll add or reduce draft. And that makes you end up changing the overall hull shape. It is no longer the same kayak. It's also a reason why scaling is a quite bad idea if you don't change the displacement at same time.

In really short; long kayaks do have more speed potential. They are not necessary faster but the way physics in water works, longer hulls can have less resistance in higher speeds. This is valid when we talk about 15ft waterline and speeds above 8km/h (5mph).

So depending of the paddling speed, hull length might have an impact or not. Generally speaking if you paddle below 8km/h (5mph) you don't need the long waterline. In other way around theoretically shorter hull should have performance advantage in slower speeds but it doesn't happen in reality. If you see this graph thingy:
http://personal.inet.fi/koti/tonivee/KOG/misc/speed_vs_lwl2.jpg
You'll notice that the dots for 6 km/h don't really show correlation between speed and waterline lenght. At 8 km/h you'll see the correlation - longer the better. However the hulls in Greenland kayaks are not excessively long. I guess the wave conditions have limited lwl. And the fact that lwl is not everything - lwl/bwl ratio is more important and actually correlates to speed much better.
http://personal.inet.fi/koti/tonivee/KOG/misc/speed_vs_lwl-bwl.jpg

In addition of speed, hull lenght and rocker effects the behaviour in waves. I've been thinking about long hull to use here in lake chop. I guess it could "ride over the chop". Not sure if it would work, but someday I will build a long West Greenland kayak and then i'll find out .

It's also difficult to say what just one attribute makes for the hull.