A case study of a new building of a Live Fish Carrier which initially was designed with fixed pitch propellers driven by 2 electric motors, showed that what was expected to be a simple and the most cost effective solution, appeard to be beaten by the efficiency from using a controllable pitch propeller.
A new building of a Live Fish Carrier was initially designed with fixed pitch propellers driven by 2 electric motors. The intention was to use full power when loaded with live salmons back to the fish factory, and only approx. 50% power in ballast transit from fish factory back to the fish farm.
The first thought was that this must be a very simple and cost-effective solution. But when choosing the design pitch (close to optimal for full power) we realized the same fixed pitch propeller was not able to utilize more than half the power from the motors at 50%, in ballast transit.
By using a controllable pitch propeller we could utilize the power from the electrical motors in the entire power range almost from zero to 100% by adjusting the pitch, and the benefit of this in ballast transit mode was so magnificent to the ship owner that they decided to change from FPP to CPP.
The design focus was a simplistic installation with FPP and no gearbox where the electric motors should be in tandem directly connected to the propeller shaft. However, a thrust-box aft of the electric motors would anyway have had to be installed in the shaftline. With Brunvoll’s very compact combination of thrust-box and oil distribution box for the propeller pitch, it still became very compact and in addition a flexible CP-propulsion system with much better energy efficiency for the ship owner.
Selected Brunvoll references