: Mariner Kayaks are available with a sliding seat. Their web site explains the
: changes that occur with moving a seat fore and aft.
: http://www.marinerkayaks.com/

: Moving the seat forward would likely make the kayak broach even more readily.
: Shifting it backward should reduce broaching to some degree, however, it's
: the overall design of the hull that makes the biggest difference. If the
: boat is somewhat large for you, it will ride high in the water and be more
: apt to slide around on waves and broach, so perhaps you're on target in
: thinking about a narrower boat.

Moving the seat also alters how the boat handles in a cross wind. Moving the seat back puts more of the stearn into the water and more of the bow out of the water. Now add a cross wind to this picture and the bow will move more easily down wind and the stearn will resist moving down wind. If your boat tends to turn into the wind moving the seat back will help in a cross wind. If you boat tends to turn down wind moving the seat back will make it worse.

A good boat design for your weight (including gear) is one that tracks in the water and in a crosswind with the seat in the same location.