Most modern Personal Water Crafts come fitted from the factory with an adjustable trim feature. This feature allows the rider to adjust the trim of the watercraft – in simple terms it adjusts the height that the front of the watercraft is out of the water.
It does this by adjusting the angle of the jet unit outlet at the back of the ski. With the unit pointing down this will drop the nose of the watercraft and with the unit pointing up it will lift the front of the ski out of the water.
With the trim set high, so the front of the ski is out of the water the ski will have less drag in the water. With less of the watercrafts hull in the water this will mean it should go slightly faster, but on the same note it will be less responsive in the steering ( This is suitable for going fast on flat water0. There is also a down side that when it is at high speed your ski will become less stable.
With the trim set low, so the front of the ski is lower in the water the ski will be a lot more aggressive. It will turn in a lot harder which is suitable for short tight courses and also choppy water. This keeps the ski safely in the water and not making you jump off the smallest waves.
You can also use your trim to counterbalance extra loads, with a passenger on the back or if you are towing a ski biscuit or skier/wake-boarder I would recommend having the front of the trim set down so the front of the ski sits lower in the water. Doing this will make up for the the weight that will be pulling the front of the ski out of the water and vice versa if for some reason you had a heavy load in the front of your ski you can use the trim to counterbalance and bring the front of the ski back up to a suitable position.
Want to go fast … Nose up.
Want to turn aggressive .. Nose down.