I sure wouldn't want to be a diver when that thing passes above. You'd be 'screwed' in the most literal way.
PT, you should come down and dive in the St. Lawrence some time... You end up right under the lakers as they go by. It's a good incentive to make sure your bouyancy is under control! It's not so much a sound you hear, but a percussive thumping... rather like a large sub-woofer!
