OK, I'm not going to reply to any specific post here, but, I think that some of us are missing the point.
Tipping, in my humble opinion, is a reward, or a thanks, for a job well done, and...........certainly, is discretionary. Not as an incentive for better service now or in the future. That in itself automatically assumes that one expects the service will be less than excellent.
A mate on a charter generally works his or her tail off to make "your" day enjoyable. If they don't they generally don't last more than a trip or two. If they do, they are certainly worth 15% of the cost of the day.
I tip relatively well in restaurants, if the service deserves it. If it does not then I don't. I over-tip breakfast waitresses. In general they get stiffed by the majority and by the restaurant owners when tips are left on credit card transactions. I have seen a waitress work her butt off to serve a table of 8 or 10 breakfast then get $5.00 at the end of it.