In ship design, one aims for minimizing the ships resistance or the required power. Ideally both hull and propulsor are optimized together to achieve the best combination possible. For twin gondola's, this combination is of great importance, due to the asymmetric nature of the flow coming into the propulsor. Dang, Hao, Rueda and Willemsen (2015) have shown an optimization for a single screw ship with an asymmetric aftbody. This asymmetry generates a swirl, which is then present in the wake field and is thus felt by the propulsor. The resistance using this design showed a decrease of 1.8%, while the required power decreased with approximately 6%. This indicates that although resistance and power are related, the required power is also dependent on the wake and the swirl coming into the propeller.Van Berlekom in 1985, presented some main design parameters for twin-gondola's. He also mentions large performance differences between inward and outward rotating propellers of up to 15%. In the same workshop, Jonk (1985) also presented work on twin-gondola's about the influence of both vertical and horizontal angle of the gondola on the performance.