There is! It is the Northern Canyon, on contract to Centrica. Operator Hallin Marine ( www.hallinmarine.com ). Vessel has both ROVs and diving spread onboard. Operating in Morecombe Bay area now until approx beginning of February 2010.

Operating cost per day of the Northern Canyon > Hull value of of a PA30 so unlikely to be worthwhile. I need to declare personal interest - but happy to help if someone wants it back :)

Well your RIB must have some pretty fancy equipment on board as I've not come across an echo sounder that gives usuable data at that speed in a RIB either!

HTC

But if you lose the pressure in the dom the prop. is out of control and you can't feather the prop.

Big Blue Scuba Divers in Port Vila,Vanuatu have recently sunk a twin engine Pipe Comanche Twin engine aircraft for recreational divers to enjoy while also creating an artificial reef for marine life to enjoy!

YouTube - Big Blue Vanuatu

Aircraft recovered:

BBC News - Crashed plane recovered from seabed

Six months is a long while between ditching and recovery plus there is likely to be quite a bit of recovery damage, it will be very interesting to see what is found wrong with the aircraft.

AAIB bulletin report:

Air Accidents Investigation: Piper PA 30, M-ALAN

How can one have an uncontrollable overspeed condition if the throttle and mixture are both working and the engine power generation can be totally shut off?

My understanding is one must slow the aircraft down to the point where the RPM on the fine stops is within the target range in governor failure modes such as described. There is no indication in the narrative this was attempted.

If there is enough airflow (speed) to overspeed a prop which is against its fine pitch stop, with the throttle shut, then surely shutting down that engine is not going to make much of an additional improvement.

As you say, one needs to slow down a bit.

Prop runaway: options
 

Easy to judge from the couch and not being in danger:
vyse and zero thrust on the engine will keep the prop well below max. RPM when the propeller is at it's most fine position with no pressure against oil pressure.
Some reduced positive thrust will be possible at blue line with max. RPM.

Shutting down the engine doesn't help at all, because the propeller continues windmilling. You can't feather a runaway prop unless cutting oil pressure and having left some opposing pressure (nitrogen or spring). Windmilling engine creates its own oil pressure.

Even a very lightly loaded TwinCo will hardly hold 3000 ft with a windmilling prop.

These thoughts are no judgements for the decissions on this flight, but should help others in a similar case.

Regards and safe flying,
Andi