I was a charter boat owner for a while and I tipped dock staff $20pp anytime they caught my lines or helped me off the dock. If the folks who cleaned the boat were around $50. Operations staff $75-$100. Office staff, when they assisted me or my guests $10-$20, depending. It probably cost me $300-$400 per charter, money well spent.
I always tip dock staff $20pp at fuel docks etc. Whether it’s bribery or not, when I tip after coming into a dock, the workers always pay special attention when helping me off the dock.
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