: . . .I started thinking about it (dangerous) and I have a very
: rough idea of how I'd do a sliding seat. I think I'd put a
: .25"x.75" aluminum or CF ridge down the center of my cockpit and
: imbed a matching slot into the seat bottom.

The siding seat idea sould be do-able, but I'm not too fond of that center ridge idea. I think the rise of the seat needed to fit over this ridge would be greater than you anticipate.

With a rail 3/4 inches high in the center of your cockpit, the seat sliding along it would need to be at least 1 inch thick -- and probably 1 1/4 would be stronger -- so that it doesn't break in half. Otherwise, that rigid ridge might act like a log splitter. A thin seat base will flex on those ball bearings (the ridge will stay ridgid) and weight put on opposite sides of the ridge will have considerable leverage. Bearings or not, this is a teeter-totter.

That thicker seat base is now going to need the same foam on top of it as your curent seat -- so you'll end up with your seat being somewhere over an inch higher. That might affect your center of gravity.

Unless you are planning to row, and want a sliding seat like rowers use, I think the ball bearings are not necessary.

I'd opt for a thin "bucket" seat base, say 1/8th inch plywood or strips, covered on both sides with glass and epoxy and bent in a shallow "u" shape to fit the curvature of the bottom of your cockpit. Slide this into two thin rails of metal or wood which are fitted to the sides of the cockpit, just above the floor. You will want a loose fit so the bucket can slide freely when it is not loaded. siting on it,though will let it flex a bit and come into firm contact with the bottom of the kayak. But the track will hold it in should you bail out.
Any kind of set screw will hold this in place. If you want you can drill holes near the edges of the sliding bucket and use a pin or dowel through them and the track to hold it fast.

Mount your seat to the bucket. If you want to adjust the position while underway, pull the lock pin, or loosen the set screw, pull yourself up a bit on the coaming to get the weight off of the seat base, and slide it around. then retighten the setscrew.

A sling type back rest would be adjustable if you choose to not incorporate the seat back with the seat.

As for footpegs: the sliding bucket might be made strong enough to support footpegs. Not sure how strong that would have to be, though.

Or, looking at things from the other end, if you connect your seat to your footpegs, then by using your footpeg adjustments you could change the position of your seat. No center ridge needed with this scheme, either.

Just some thoughts.

PGJ