"Can these things get under Correyvreckan?"

I wouldn't bet against it, Dave. There's plenty of depth of water through the Corryvrecka. Although there's a pretty powerful race at certain states of tide they have plenty of power, and as long as they avoid the rock pinnacle it ought to be perfectly possible. Whether they'd choose to do it under normal circumstances is open to conjecture, though.

I've sailed through the Corryvreckan(in a pretty substantial schooner), and an exciting ride it was too!