Here is a video that I put together a couple of years ago of my niece wake boarding up in Maine. It's definitely amateur, but it's good for making a few points.
This was all hand flown from ashore, and although one of the tracking modes may work, I don't think you would get the variety of angles to the boat and skier that make for a nice presentation. So, hand flown - IMO - is the best option.
Filming a water skier will definitely make you a better UAV pilot. It is a very dynamic type of operation, and unless you are actually on the boat, you will not know exactly what it is going to do, and if you plan on going one way, and the boat goes the other, it could be some time before you're on it again.
Assuming maybe a twenty minute flight, you will generate about that much footage, but in the end, after going through it all and editing out the parts that are jerky and/or off center, you will only have maybe 4-5 minutes of usable footage. So, my suggestion is to stop the recording very briefly multiple times during this twenty minutes in order to generate multiple smaller files. I have found this makes it much easier to review and work with the footage after.