I suspect the performance in pulling up a water skier with a SPORT 15 hull with a 70-HP four-stroke-power-cycle engine will depend on many variables, including:
- the weight of the water skier
- getting up on two skis or one ski
- weight of crew in the boat
- propeller in use
- point of attachment of ski tow rope to hull
- proper engine trim at start
- proper handling of throttle position during acceleration
The 15-foot hull is a very excellent small boat, but it is not particularly designed for use in water skiing. I have seen a 13-foot Boston Whaler with a 35-HP engine pull up water skiers on two skis whose body weight was not more than perhaps 130-lbs. On that basis I would expect that a 15-footer with 70-HP should be able to pull up a similar load.
Choice of the propeller configuration will also be a big influence. For pulling up a water skier the propeller pitch may need to be changed to be lower than usual, and the number of blades may need to be increased for better results in accelerating under heavy loads.