Hmm I am almost frightened to say this, but it seems I may be on the way to getting it sorted out!
I started by removing all the wires, totally ! Everything unplugged and removed ! All servos disconnected and batteries removed.
I have replaced some of the power supply cables with Shielded cable. One way or another that interference wasnt going anywhere !
I also took manksters suggestion, as in the Ferrite rings. I went to RS yesterday and ordered lots of the things. You would not believe how hard it is to order those over the phone. The poor lass on the order line thought I was trying to order Ferrit rings ?

I thought "Ahh shes heard about this stupid boat as well and is taking the P

ss!" The pressure must be getting to her !
So now all the power lines have the tubular rings, and the servo wires have the clip on type. They really do make a difference. I also removed the power line to the reciever pack, which was connected to a Futaba servo extension, and I braded the wires by hand, I dont like wires running in one length, slightley concerned about Induction.
Getting a bit paranoid now
I also bit the bullet and bought a new set of Crystals. I dont know if the old ones were dodgy, but not taking the chance. And while I was on I rang Subtech about the transmitter. And Dave seems to agree with me in that the Transmitter is partially responsible for the problem. He is confident that the batteries are shot. So more on there way!
So after all that was done I carefully powered it up, and all quiet ! Nothing juddering, noting twitching

I am nervous about saying its sorted, because its probably not knowing my luck, but hopefully on the way. The only thing I am having bother with is the switch for the bow thruster. The switch for it just wont work on my transmitter. But either the new batteries for it will sort it, or the handset is going back to Germany for repair. Apparently it wouldnt be the first one to make the journey
Anyways, enough for now, work beckons tommrrow!
Paul