Synchronous motors help test ship propellers

A Siemens Automation and Drives product story
Edited by the Engineeringtalk editorial team Apr 20, 2006

Synchronous spindle motors being used to undertake performance tests on ship propellers at a hydrodynamic test facility in the Far East.

Two 1FE synchronous spindle motors from Siemens Automation and Drives are being used to undertake performance tests on ship propellers at a hydrodynamic test facility in the Far East.

The contract win comes via Cussons Technology, a UK-based test equipment designer and supplier, which had a requirement for motors demonstrating high levels of control and torque performance, as well as high power density and a suitably compact design.

Based on the same site at Salford for its entire 120-year history, Cussons Technology primarily makes educational equipment for teaching engineering science up to degree level.

However, when the company acquired a German firm that specialised in products for the hydrodynamic testing of ship and submarine models, Cussons saw a niche in the market.

That was seven years ago and today Cussons designs its own products for this sector, which represents a significant and growing slice of the company's £3 million annual turnover.

Customers in this industry typically require accurately scaled test models of surface ships and submerged vessels, some up to 12m long.

These are used for propulsion, resistance and manoeuvrability testing to predict the performance of the full size vessel before manufacture.

The task for Cussons is to supply hydrodynamic equipment to help test the models for research purposes.

This usually takes place in specially constructed towing tanks or ocean basins at test facilities around the world.

Towing tanks, which are probably best described as mini canals, vary in size and can be up to 500m long and 8m wide.

The contract involved the design and development of a dynamometer for propeller performance tests.

The equipment had to be capable of testing two contra-rotating (one turning clockwise, the other counter-clockwise) propellers simultaneously.

Cussons required two powerful but small size submersible, synchronous motors to drive the propellers, which run on co-axial shafts (one inside the other).

"We had to measure accurately the speed, torque and thrust generated by each propeller", said Engineering Technical Director Peter Hughes.

"There are several benefits to selecting the Siemens 1FE synchronous motors".

"Traditional equipment for these applications used air cooled motors positioned above the water, with drive shafts and gearing going down to the submerged dynamometer".

"However, this design has inherent problems with mechanical noise and the bulky physical size of the completed assembly".

"Using the Siemens motors, we have been able to build them directly into our dynamometer and use a direct drive to the two contra-rotating propellers, thus eliminating external drive shafts and gearboxes".

"The end result is a far more compact and quieter running machine".

Other factors that Cussons outlined as crucial to the selection process were control functionality and the ability of the motors to generate torque from standstill right up to full operating speed.

Originally Cussons constructed a prototype dynamometer to test the 1FE motor performance, and this was tested in the factory on a dynamic calibration rig, which was designed and built by Cussons.

This rig also uses 1FE motors which act as generators to apply accurate torque loading when connected to the dynamometer propeller shafts.

The 1FE motor range from Siemens was originally developed for machine tools.

The built-in 1FE motors are effectively shrunk directly on to the motor spindle, thus reducing the entire spindle head volume despite having the same performance.

With their high power density and speeds up to 30,000rev/min, the motors are for where high demands are placed on machining quality and precision.

"We have tried other vendors in the past", said Hughes, "but we've used Siemens successfully for a number of years now".

"The performance of its products is always excellent and its range of motors is very widespread".

"Also, Siemens religiously meets the delivery schedule, which is critical in time sensitive industries such as ours".

The dynamometer is being tested at Cussons Salford factory before being transported to the Far East.

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