Thanks for the link, Jonty...but I think I've won with it now. It fought me all the way, but I think I've managed to thrash it into submission now. Just having a smoke and a coke, then I'll give it a try in the bath.
I had to change the motor(yet again!)it now has a low drain 385 motor turning a 30mm 3 blade plastic prop, which I may change to a brass one later, the previous motor still didn't have enough grunt, but this one should have. I can hide it easily enough later on when the time comes. I also want to lower the rear deck section where the motor sits, it's a bit too high where it is.
Rich