The motor in that stand up is a 4 stroke. The ski is made from Hydrospace and the motor is based off of polarises 140 motor. Which in fact I think is but with more tweaking.
They where supposed to have 3 motor options for the Hydrospace stand up. A 2 stroke, the 4 stroke he had and then another 4 stroke with a turbo.....only one is available at the moment.