Have a look at the pictures on these websites and see if your kayak has
a similar design:

http://www.canoeslalom.co.uk/
http://www.jacksonkayak.com/kayaks06/ricochet.cfm

wrote:
Thanks for that, I hadn't thought of cutting them that way!

That might be an easier way of going about it. I'll have another look
at them with that in mind!

As for kayak type, one has Kiwi (Perception?) and Slalom on it so I'd
guess it is an old slalom one as you suggested. The other one is
unmarked.

As you say, I've little to lose by experimenting!

Cheers,

Nick