Well my philosophy is tip as much as you can. It should also reflect the work that the crew did. If i think the crew wasnt good i wont tip as much. Most of the time those deckhands work hard and deserve a little appreciation. Between me and my dad on the last overnight trip we gave them 60$ on top of galley tab and fish cleaning. That was well worth it. For only one pearson on an overnight trip 20$-40$ isnt uncommom.
hope that helps
Daniel