Zdupell 15 to 20 % is with in reason your trip is 5 t0 8 hours and only you and your partners will know how hard the mate works .
just think people have no problem tipping a waitress 20%when you are out at a restaurant some places don't even give you an option they add 18% to your bill and the time of a meal runs 1.5 to 2 hours
so bottom line if your mate works hard for you let him know.both CAPT and MATE along with you and your GUESTS will look forward to your next trip