So a wide range of high power motors will be available and these could provide some interesting benefits on propulsion systems on small to medium sized vessels. For example the propeller would no longer have to be mechanically connected to the engine with a long rotating shaft. It would be replaced with hydraulic pumps and just three hydraulic lines to the motor, eliminating all the engineering involved in designing and installing the long prop shaft and the cost of the shaft and bearings needed. This also frees up the possibilities of positioning the engine and propellers to anywhere in the vessel to suit the application.

Hydraulically, a number of propellers can be powered from the engine thus opening up more possibilities. Two or more engines can be used to share the power between the drives, providing the opportunity to look at the basic vessel design andmake improvements, for example to improve the weight distribution. It also means that all or some of the power can be diverted from the propulsion to other vessel requirements such as deck equipment when the full power of propulsion is not needed.

More than one engine then gives some possibilities for redundancy and therefore extra security if needed. If the pumps used are variable displacement this means speed can be controlled independently of the engine which would run efficiently at a fixed speed and, with two propellers, could be used in a steering mode with one in reverse and one in forward.

The hydraulic motors can even be used in submerged conditions and are maintenance free, providing long and reliable life. They are also quiet compared to mechanical drives because there are no high speed elements involved. The mechanical efficiency of these motors is approaching 98%, similar to that of a roller bearing.

MJ Information No: 21205