Hydraulic motors show marine drive potential

Edited by the Engineeringtalk editorial team Oct 28, 2005

New ideas made possible through progress and product development are worth thinking about and the new CBP motors from Hagglunds open up some interesting ideas in marine propulsion.

New ideas made possible through progress and product development are worth thinking about, and the new CBP motors from Hagglunds open up some interesting ideas in marine propulsion.

Hagglunds Drives has been manufacturing hydraulic motors since the 1960s - originally for cranes but since the 1980s on heavy duty continuous industrial drives - and now the latest development is a high power drive unit available in several sizes that will give power up to 1MW from a single motor.

Of course with hydraulic motors it is very easy to connect in parallel to share the load and with through shaft design you can also stack the motors on a shaft to multiply the power available.

The speed range available from the new CBP140 motor is up to 320rev/min, dependent on the specific displacement, and within the CBP140 there are four sizes to choose from and the company is planning for four more and bigger motors in the range CBP280 to CBP 840.

The model designation CBP140 means 140Nm/bar torque is produced, and so with a constant pressure of say 175bar a torque of around 24kNm is produced.

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.

Therefore shipbuilders can eliminate 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.

Of course, hydraulically a number of propellers can be powered from the engine, so opening up more possibilities.

Designers can also use two or more engines and share the power between the drives.

This provides the opportunity to look at the basic vessel design and make improvements with this new versatility and flexibility of major components, 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 for example 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 with mechanical drives because there are no high speed elements involved as gearboxes are eliminated, the motors provide high torque without the need of speed reduction units.

The mechanical efficiency of these motors is approaching 98% similar to that of a roller bearing.

The motors and pumps being standard proprietary items are available on short lead times, and Hagglunds has a worldwide network of sales and service facilities to offer support wherever you may need it.

There are many other characteristics of Hagglunds motors which may be attractive too, such as the almost negligible inertia which brings a response to the drive impossible for geared drives to emulate for example to give fast stopping in emergencies or for starting and stopping frequently with controlled ramp up and down times.

The high torque from the motors is available irrespective of the speed so high starting torque is a characteristic and it may be possible to improve propeller design to take advantage of this feature to operate at lower speeds and therefore lower noise levels.

The drive arrangement is very simple and installation easy.

With flexible hoses connecting the motor it is also possible for the drive to move during operations so opening the possibility for the propeller to slew or move up and down with the close coupled drive.

This technique is already used for example on dredging cutterhead drives.