Assessing seakeeping performance at an early stage is even more important for wind powered vesselsthan for conventional ships, since there is little design experience to lean on. When the driving force comes from sails instead of a propeller, ship dynamics change considerably. Course keeping, turning ability, motions and acceleration in waves are just some of the properties that must be assessed. Including wind propulsion devices in a model test is however not straight forward. In this paper we present a methodology for model testing wind powered vessels. Rpm and azimuth-controlled fans/airscrews are used to mimic the aerodynamic forces from the sails. Results from model tests with a car carrier are presented and discussed while particular attention is paid to possible improvements of the test methodology.