Mainsheet Swivel Jammer

[Alan Price 543]

Hopefully I will be sailing my Supernova a lot more this year than the last couple and I'm thinking of fitting a swivel jammer. I've seen some that are a base,arm and cleat unit but need a block attaching and thought of using the original rachet block thats on the boat that is on a lace eye at the moment.
Any thoughts or tips on type to use and ,just as important, fitting it securely would be most appreciated before I go blundering in.
Looking forward to seeing you all again at some opens.
Thanks,Alan.