I would suggest replacing any suspicious wiring before taking the boat to the water.

Thanks Dave 976 - model has been stored in garage for the last couple of months, having last been used in November - replacing wiring in a Billings Swarte Zee is not an easy option - access below decks in very tight - will keep testing on dry land, before next water test. Fortunately a water test is safe, as we have access to rowing boats to retrieve recalcitrant models. Replacing the wiring is a last resort.

Hi luckyduck
Glad to hear Colin's suggestion cleared your issue. Any RC gear that has not been used for sometime can suffer from bad connections. I suggest you carefully inspect all your Rx, ESC and servo connectors for any sign of corrosion or damage. Black wire syndrome used to be a problem and may still be, especially after a winter laid up in a damp storage area. If you do find any damage I suggest you replace the whole wire and connector as the problem not fixable and is likely to reappear and your model may be in the water next time.
dave976

Have you tried plugging the steering servo into the speed controller socket, if so did it work ok if yes then looks like the speed controller, I may be trying to teach granny to sick eggs here ;-(
OOps didn't find the replies, sorry!!

Swapped channels as you suggested Colin, and all works. So replaced correct channels and all still works, just needed centralising the esc. So it seems that just unplugging and plugging back in servo cables into receiver cleared whatever the problem was - just goes to show that such a simple operation can solve a problem. thanks again

Thanks Colin - will have to try swapping channels as I do not have a tester.

Try the esc in the rudder channel, or use a servo tester, to check that the esc is working.
Cheers Colin.