In the next decades the RN will replace both its STOVL aircraft and its Carriers. The design of the aircraft and the ships will be fundamentally linked. The main contender for the aircraft is the STOVL JSF but the USN criteria for safe launch of such aircraft are based on flat deck operations. The RN have differently expressed safe launch criteria based on a ski-jump take-off. In addition, for a ski-jump vessel trade-offs are possible between ship characteristics: speed, ramp angle, deck length and aircraft characteristics: Rates of Rotation, launch Angle of Attack, undercarriage strength.Using a DERA code APOSTL and a simple generic STOVL fighter model this paper investigates the differences between the flat deck and ski-jump launch criteria and illustrates the gains and disadvantages of using steeper ramp angles, increased Wind over the Deck, Rates of Rotation and launch Angle of Attack.