I think gratuities for people that assist in travels is appropriate...porters, taxi drivers, etc. Dock help, I think that sorta depends on how much help. I would always tip for the boat checkout and briefing person as that usually takes the better part of an hour of their time. Many restaurants are now adding a "service fee" to your bill. I will usually add another 5% to that depending on quality of service. If the service fee is not included, I usually tip around 20%, depending.