I'm a commercial boat driver and drive a dive rib for a North Sea technical services company and I don't think that Southampton or the Isle of Wight will provide you with testing enough conditions to have your skills honed.
This is a bummer because it's where our school is based also
Three of the best Boat drivers, and one of the best personalities I have ever met are based in a company called Safety Boat Services. James, Iain and Jon are all North Sea Veterans and commercial and sports divers.
and it's close to the Dutch ferries
Dave Mallett Wavelength on this forum also has a good and I am told is a very sound guy. http://www.powerboat-training.co.uk/...Wavelength.htm
Also as I recall theres a school in Banff . 58 North I think they are called which has a good training seahttp://www.north58.co.uk/ That's right up the top of scotland where they let moose roam the streets. I don't know this school but I saw the place when I was up there in a tug a few weeks ago and it looked like a good set up