@Roy Gardiner it was once classed as unnavigable. But with modern powerful boats it's no big deal any more. I've some German marine ships powering straight through the standing waves at the height of the whirlpool running. RNLI Oban I believe sometimes deliberately goes in it for training purposes, possibly the Islay boys as well.
@Armin Grewe I was thinking not so much of danger to vessels, more to swimmers. I just did a bit of research and found this https://whirlpool-scotland.co.uk/ . I certainly would not fancy my chances of surviving if I fell in there.
@Roy Gardiner it's all about timing I know people who have swum it, they are pretty normal people. I'm not sure how long the window is, but during slack tide it's perfectly safe (well, if you have a support crew) and quite a few people have swum from Jura to Scarba (and back, I think). But you're right, if you fall in while it's running you're in deep deep trouble.