They've not yet shown any sign of being a danger to the hull as far as I know. They pretty often break the rudder off leaving the boat difficult to control. Most long distance sailors would carry some kind of emergency rudder arrangement but more casual coastal types don't usually.

Speculation among sailors is that "hey, did you know you can break bits off those things?" is as plausible an explanation as any.

There are known ways to scare orcas off but it's illegal to distress them and nobody really wants to. I certainly don't.