It's very serious stuff indeed, and not to be messed with! The Admiralty Charts of the area describe it as 'un-navigable' but it can be sailed through with care at the right state of tide. I'd be very nervous about taking a small boat through at any time, although I have seen film of people kayaking through there, and even scuba-divers diving on the submerged (49 metres) rock and scourpit which causes the whirlpool/wave (albeit only for a 20-minute period around slack-water).

J :0)