Thoughts on his advice for keeping your butt off the seat back? Especially in the realm of a fast kayak hull?
A K1 sprint kayak doesn’t have a backrest at all. The backrests for my “fast kayaks” (Rapier 20 and 18x) are adjusted so that they don’t touch my back unless I stop paddling and lean backwards to rest.
On a surfski bucket or a kayak backrest if you press hard against it while paddling and have strong leg drive and rotation, you will chafe badly.
Oscar talks about leg drive pulling his bum off the seat, rather than just pushing himself back into the seat. My mental key is that my butt rotates (spins in place) on the seat as if I am sitting on a record player turn table.
I have a K1 rotating seat on my kayak erg. It’s a great way to really feel how your butt should be rotating in the seat (and not pushing yourself backwards with your leg drive). Most of the rotation is done low, in your hips, not high up in your shoulders.
Here’s a video of my setup, showing leg drive and “butt” rotation. You can certainly do this in a regular seat (may need to wax it or sit on a plastic grocery bag), but the rotating seat makes it easier:
I cannot address racing, but for long days on the water it is very important to engage the abdominals, trunk and lower back into your strokes. Arm paddlers always get slow in the second half of the day.