This is a tough one... On some of the boats I go on, their are good crews, and sometimes I tip, sometimes, I dont. I think thats what they are there for, and for a two tank trip, it just went up to $60. Thats enough money out of me.
Now, other boats I go on, the owner is the operator, and sometimes, his son is there to help crew the boat. I have no problem giving the son a tip, but not the owner. It just seems wrong to give him money for the charter, and then another extra bit of cash too.
I dont know. I;d be interested to hear what others do...
Also, a liveaboard is a whole other story, I tip basically $10 a day for good service...