Thanks for your replies
Firstly, we didn't choose to have a cat initially. He 'adopted' us when 6 years ago someone from a nearby house moved away and left him behind. We were one of several house he called upon.
We would love to take him with us, but he is very nervous and feel he woudn't adapt, especially when we'd be cruising. Also, if he did get disorientated and lost, that we feel would be unfair on him.
As for the comments implying that we are being unfair/cruel/irresponsible I don't think we are, because if you read my OP I said we wouldn't move onto the boat until we were happy he was re-homed properly. They say you never actually own a cat and because they are such independent creatures I would have no qualms about it if he went to a good home although we'd miss him terribly of course. Cats aren't known to be as reliant on and become as attached to specific people like dogs do and I have no doubt he would adapt and be very happy ever after.
It is because we are caring people and very fond of this cat that we are prepared to do whatever is necessary to ensure that he doesn't suffer. And, whilst we will do our utmost to find a good home for him, even though you don't know this cat and what he's like, I do take on board your comments about how well cats adapt to life on the cut, and we might well try it but only after this other option has been explored.
Neil