Lian BlacquiereYacht charter broker, DMA Yachting
15 to 20% of the base charter fee is customary, with motor yacht crews at the higher end of that range. It is always at your discretion and should reflect the service you actually received, but plan for it in the budget from the start; on a $60,000 week that is $9,000 to $12,000.
The practical side: the gratuity is handed to the captain at the end of the charter, usually in cash or by pre-arranged transfer, and the captain splits it evenly among the whole crew, including the ones you saw less of, like the engineer who kept the air conditioning running.
If service ever falls short mid-trip, tell the captain or your broker then, not at tip time; almost everything is fixable while you are still aboard. Full budget math in what a Bahamas charter really costs.