New trends in the offshore wind industry show that wind farms are being built further onto sea. This also means that turbines have to be installed in deeper waters resulting in new challenges for the offshore wind industry. The commonly used jack-up vessels have a limited operating depth and therefore floating installation vessels become an interesting alternative. The downside of using floating installation vessels is that they encounter more unwanted motions. A motion compensating tool can help to decrease the negative effects of the unwanted motions. The designing steps for a motion compensating tool are presented resulting in a final concept design. The concept is eventually worked out in a mathematical model to evaluate the dynamic behaviour.