Through use of state of the art tools for flow analysis the aims to establish a methodology to determine the performance of a high speed planing craft both in calm water and in waves. Verification against full scale measurements is conducted. The ability to maintain speed in waves is of great interest -both with respect to added resistance and with respect to safe operation and loads on the crew from accelerations. Full scale measurements and CFD (Computational Fluid Dynamics) were conducted on a Norsafe Magnum 850fast patrol boat. The measurements have been conducted during a boat challenge along the Iberian coast. The challenge was run in advance of the HSBO (High Speed Boat Forum) which was held in Lisbon, Portugal, May2015.CFD simulations at similar conditions to the measurements are used for validation. It is further shown how CFD can be used to expand operational envelopes beyond the point where full scale measurements are applicable. This is especially relevant for the acceleration loads on the crew which is often the limiting factor of small HSC (High Speed Crafts). Pressure loads are extracted from the CFD and are evaluated against the current standards for life boats. Various criteria are discussed and the most relevant are analyzed for the measurement results and the CFD simulation. An operational envelope where the different criteria are combined is suggested.