+1 ... IMO this is the best way to do it.

On my boats I use a standard long cockpit but not a keyhole ... and I contour the forward section of the cockpit such that the deck overlaps my knees and some of my thigh. For a good example check out any Mariner design and Brian Schultz' F1. Advantages are that your knees get very good purchase, the fit is good and not fussy, it's easy to fit-out and it allows more options as to where you sit than hooks.

Ken Blanton

: Another strategy would be to make a 'keyhole' cockpit opening,
: where the deck forms the knee brace and the coaming rim width
: varies.
:
: http://www.atlantickayaktours.com/images/retail/Kayaks/NDK/Romany-HV/Knee-Bumps-top.jpg
: There are lots of commercial examples of this.
: I'm building a boat inspired by commercial designs right now, and
: the better commercial boats have a pronounced curve on the deck
: to form the knee 'bump' or recess. It's not easy to duplicate
: with strip construction - easier to just make the deck a smooth
: profile and then pad down with foam.
: If you can have a 'good look' at a bunch of (good) commercial boats
: you will get the idea pretty quickly.

: If folks of different leg lengths are to use the boat, there has to
: be some fore-aft flexibility built in. The seat position is
: pretty well 'locked' (relative to the center of buoyancy) so
: knees will fall in different positions. So think 'trough' for
: the thighs.
: As for dimensions:
: On the NDK Romany, the keyhole-shaped cockpit cutout is (all
: dimensions approximate) 32.5L x 15W. The 'keyhole' at the
: forward end extends back about 10.5" before it flares out.
: The width of the keyhole area is about 8" at the front,
: 9.5" further back. The outside of the coaming rim is a
: smooth oval-like shape 35.5 x 18.

: Even without the keyhole, it's possible to make a good thigh 'grip'
: without padding (other than a thin foam for comfort), with the
: right deck shape. The Mariner kayak decks were built to
: accommodate the sliding seat and are comfortable (for me) with a
: seat position that can vary 8-10" fore and aft. It's all in
: the deck re-curve shape.

: Have a look at the NDK Pilgrim for an example of prominent 'knee
: bumps' - not something easily done with strip construction!

: I don't much like the 'sticking out fin' style of thigh 'hooks',
: though they are popular.