Yes You should do something.
If the NOR says... MUST HAVE LIABILITY Coverage.
I would ask each person at registration... Do you have liabiltiy insurance? Yes or NO!
Make them LIE TO YOU....
Make it CLEAR TO THEM ... that this matters to the people running the regatta and the people in the regatta. Its not just a little white lie. So... Choose...
Lie to your friends and competitors or Do the right thing...
Now... if liability insurance coverage does not matter to you and your buddies and it does not matter to the Regatta organizers... ... Take it out of the NOR.... You don't have to insist on Liability.. . This is Mary's point of view. Hey.. Its not the regattas problem if you have an accident.