To control and increase human performance in the maritime field a methodology to measure workload and performance is needed. This paper describes a developed methodology using different techniques to assess performance, mental effort and operational demand. Physiological measurements and subjective effort ratings on one hand are combined with subjective performance observations and independent simulator data on the other hand. A secondary task is added to determine the mental spare capacity while performing the primary task. More emphasis on this primary task automatically results in impaired performance on the secondary task. The additional value of this methodology is the combination of several parameters to identify the performance, workload and demand. The certainty increases when more parameters point out the same direction. The feasibility of the methodology is demonstrated in a manoeuvring simulator. The experiment results confirm different demand levels. A comparison between experienced workload during the simulator training and the real operation on board is illustrated by a typical example of both physiological results and subjective effort rating. The results help to raise the awareness of task demand on experienced effort and task performance. In the future, when the methodology is optimized to a direct feedback tool, interesting opportunities arise to take into account the human performance in training and research.