The booking agent will have the correct answer for you and your charter.

A crewed charter is typically offered 10-20% of Charter total. The agent handling the charter will explain the process, and the customary gratuity. Before your charter, you will wire an Advance Provisioning Allowance to the boat. This will cover your fuel, docking, provisioning, water, etc. The captain will reckon the total on your final night or morning. At this time, it is typical to review the charter with the captain and offer tip for the crew.