Mil-26Man, perhaps I should have written 'were moored to the bank' at the time.
A sailing boat was coming down the broad under sail when the helmsman lost control of the sail and promptly turned 90° port directly towards our boat. I watched unable to do anything except warn everyone else as it rammed us amidships, allowing the river to rush in. I stepped off onto the bank and we all stood there watching as the boat slowly sank....
Why the helmsman didn't simply release the sail and put the helm over, we never did find out...