I have many different shaped sea kayaks, ranging from a 19 ft waterline x 21 inch beam to a 16 ft wl with 30 inch beam.

My boats also vary somewhat in rocker V and bilge shape.

I paddle regularly with the same two or three people, one of whom is a massive Shrek-like brute (6 ft 3in ±250 lbs)
No matter what this guy paddles he blows everyone else away. The result, he has to paddle the wide sissy's boat to slow him down. It doesn't work though.

A typical outing might by 3 or 4 hours on the water averaging 7kph in varying conditions. At this fairly good ground covering speed one can still hold a conversation and paddle without needing recovery stops. No one seems to be over-taxed, no matter what boat they may be in.

The one thing I have observed though is that different hull shapes seem to be faster or slower in differing conditions. I get the sensation that the longer flatter boats tend to need less effort in flat water, while a round hull with a little rocker seems to dance a bit on rough water and feel a little more floaty and less bogged down. This is why I like my North Star so much. I tend to paddle in choppy waters. If I was paddling lakes or wide rivers I would probably find myself in my Hound's Tooth. (Long, flat and thin) pictured below. (It is my own design).

I have a medium volume standard fibreglass NDK explorer which is a handy benchmark for speed trials with home made boats. It is s tight fit though, even though it is rated a medium displacement kayak. The main advantage I find with DIY is that one can build the boat to fit. I am quite large and I find european boats are too cramped after years of paddling US designs. A couple of hours and I just want to get out. Comfort in the boat is the one thing that enables a paddler to plod on joyously mile after mile. Boats that are designed to perfom every maneuver and fit like a glove are fine for hacking about in, but for long journeys one needs some room to move around.

The best thing one can do though is to grab the opportunity of paddling every boat that you get the opportunity to get out in. If you are on an outing swap boats for an hour with someone who is paddling an interesting looking design. If you have a DIY boat you will have loads of takers. If you have trouble getting your boat back you have a winning design.

Most of us tend to keep building compulsively. Make every boat a different design and you will have a perfect boat for every occasion.

Etienne