Well, it's been a few weeks without updates here. Unfortunately little has happened due to family issues but I can post the updates from the result of the sea trial...
Bath tub needed about 1200g of weight to get the water-line right but that was WAY too much for the boating lake. About 650g worked out ok but I had a big stability issue with waves. Some of the fellow boaters said about moving the weight up to the waterline, rather than at the bottom of the keel. I'm not sure about the physics of this, it seems counter-intuitive, but it's easy enough to try later.
The winch worked well but the modified servo was too sensitive. The slightest radio interference or nudge on the stick caused the winch to slowly pay out rope, requiring repeated stick movements to keep it in check. I'll probably throw together a simple digital on-off speed controller or see if I can find a cheap speed controller online which has a wider dead-band. I can wire this speed controller directly to the servo motor, bypassing the servo electronics.
The boat as pictured above is bare wooden boarding and this is how I ran it in the sea trial. The boards expanded in the humid air and a couple of them popped off. I always intended to varnish the deck so I dried the boat on a radiator and applied the varnish. Unfortunately the absorption of the varnish has the same effect and I'm now in a quandry as to how to deal with it. I may rip the deck off and start again, I may not.
I've also been working on the superstructure but because it's rebuilt from the original structure and some plant pots I've been unhappy with the finish. I've been round many sand/fill cycles and still am not happy.
More updates to come later, for now it's on the window-sill in the conservatory awaiting some time :)