Well after checking all these various replies I`ve made loads of phone calls and got lots of quotes.
For a 13K RIB with an excess of £250 most premium quotes were coming back between around £260 and £350 a year.
All of them had some kind of problem with the policy, boat too fast, no water skiing, large rock attached to wheel clamp, etc etc.
I`ve decided to go with a case of "better the devil you know" approach.
Bishop Skinner on the RYA Advantage Scheme have quoted me £320 with a £250 premium. But it includes legal cover which was an extra £20. My boat is insured anywhere so long as it has a wheel clamp and an outboard motor lock. (type not specified) It has to be ashore unless agreed in advanced (I can managed with that).
So hopefully I`ll not have to claim but if I do I`ll come back and let people know how the process went.
Cheers for everybodies help