Best advice I can give, Is to beware of you backgrounds, keep them simple, and approach from many angles. Most boats require unique compositions to get the best out of them. So experiment!
Since it's a ski boat, if their is a 2nd boat available, try getting some shots at speed, with your brother at the helm, and drag the shutter a bit to emphasize speed... Helicopters make for good platforms as well for this type shot...
Here is some old stuff just for ideas, not the best...
1)
2) The Background in this (the other boat) ruined what it could have been. . .
3) Not quite a Ski boat...

But try some unique angles.
4) - dont forget to take pictures on board, and under way!
5) Experiment, sometimes it works out well, sometimes it does not...
