29 x 18 is certainly within the typical range of commercial sea kayak coamings; many recreational kayaks have larger coamings that that.

I like 20 x 16 (about 19 x 15 inside dimensions) but I like a snug fit.

The smallest coaming I've seen on a production boat is about 18" diameter. Some historical kayaks had even smaller coamings...

The limiting factor tends to be the difference in deck height from front to back. The higher the front, the more easily you can get in and out. With a really short coaming, the front deck can be quite high on production kayaks. Hull depth is also a factor, as is the coaming's height and masik thickness/shape.

Best bet is to leave the masik until last so that you can mock-up and test fit different heights and placements until you are comfortable with getting in and out.

At 29" long, I think you'll be fine with 3" or so of difference between the front and back of the coaming; you may even be able to get away with less.

: Anyway - my cockpit is going to end up with a front-to back length
: of around 29" (w/ a width of 18" or 18.5") down
: from the designed size of 32".

: I don't know what's normal for kayaks - I've rarely measured
: length, I'm normally concerned with my fat (ahem) fitting
: width-wise. Most of the boats I have paddled have ample cockpits
: (Tsunami, Carolina, Chatham) (33.5" was the shortest).

: I have a 30" inseam.

: So... what's normal for your boats? How small are the ocean
: cockpits, really?

: Thanks.

: -Doug