I did this trailer some time ago, and it worked very well. The cart part was very stable, even at 15 to 20mph. The boom on the bow slipped under the grab loop, and was strapped around the hull and cinched up tight. The other end had an eyelet on a swivel ball, and slipped over a bolt that was hose-clamped to my seat post. The cart is plywood and 1x4" pine. The boom is a broken-off CF mast from a windsurfer. The ball joint is epoxied into the end. The seat tube mount was a bolt set in PVC, then clamped to a 1" wood dowel piece that had two sides carved out to match the PVC on one side and the seat post on the other.

I couldn't find the picture of the whole arrangement attached, but I could always take another if it's too hard to visualize. Braking is no problem with my high-end mountain bike, but a cheap road bike wouldn't stop well at all (I have disc brakes).

Here's some more pics:

http://home.pacbell.net/endoboy/kayak/trailer_bottom.jpg
http://home.pacbell.net/endoboy/kayak/tow_bar_deck_mount.jpg
http://home.pacbell.net/endoboy/kayak/tow_bar_bike_mount.jpg

I think I spent less than $50 for the whole setup. Enjoy...
Mark

: Has anone built a bicycly trailer for thier kayak? Seems to me you could
: combine a normal kayak cart and something like bike trailers for kids. The
: main problem I see is adequate braking.

: I don't see this for cross-country use, more like something that you can use
: to take your boat from your campsite to the beach.

: Just a wacky idea.

: Brian