mending plastic boats

I used to do summer seasons teaching sailing and fixed several fevas with the same problem.  All i did is first of all drilled the end of the crackes so they don't lengthen, then brace across the self draining channels (I used and old stainless shroud pin rack, which cut to lengh and screwed in with self tappers, this realy stiffened up the whole hull significantly and you could not twist the hull like you could previously (I would even suggest it would be a good idea to fit if you have an old boat before it splits) I then sealed up any holes with a bit of silicon sealant.  Although you could see the cracks.  It looked neat and worked for the rest of the season on all three boats I worked on.  (perhaps it could be a tempary fix till you can get the guy RS advised to fix it.  Other problem was cracks appreared where the gudgen and pintle are (I suspect due to people running aground with the rudder down).  To fix this I did the same (drill ends and seal) and fitted a piece of stainless box section which RS supplied in the hull behund the gudgen and pintle to spread the load. 

Good luck with fixing the boat but from my experience I would not touch a feva with a barge pole build quality is shocking throughout. 

Most Kayak companies will sell plastic sticks for re welding rotomolded boats (in many colours) - this will work on boats where the repair would be worth more than the boat.

Carve out an edge preporation in the shape of a "V" in the crack and then melt the plastic into it with a blowtorch (on a low setting!).

Possibly old news now but for future reference these people do plastic repairs:

http://www.branfibre.co.uk/boat-repairs.shtml