The Magazine for Underwater Professionals

Jan/Feb 2017


Subsea motor merger

In 2015, two internationally renowned offshore engineering businesses became one. Datem Ltd and Impaq Ltd joined forces, but what's the story?

Although there is a rich and varied engineering heritage within the United Kingdom, the agricultural heartland of Lincolnshire is not the first place you’d look to find a high technology design and manufacturing facility working in the offshore industry. Located on the edge of the traditional market town of Sleaford, Datem Ltd has developed a formidable reputation as one of the world’s leaders in seabed cone penetration test (CPT) systems.

Established in 1986 to provide engineering services to the offshore industry, the big break came in 1998 with the development of the Neptune 3000 miniature CPT system. This represented a new and more reliable way of using a coiled rod to push a miniature high precision geotechnical probe (cone) into subsea soils, all within a compact, easily deployable unit.

Following on from this success Datem developed a larger system, the Neptune 5000, and continues to develop a broader range of products for subsea soil investigation.

  • Neptune 5000 CPT system

However, in the early days of developing the first Neptune system, a subsea drive solution was required, and this called for specialist expertise. These were to be found within the county, a mere 35 miles (56 kilometres) north in Gainsborough, in the form of an equally young business, Impaq Ltd.


With 12 years of experience in marine engineering already behind him including working as a design engineer for Hoad Design & Engineering Ltd, UK, John Rodgers, an entrepreneurial professional engineer, spotted a gap in the market. In 1992 Impaq Ltd was born to support the growing subsea ROV industry.

Datem and Impaq began a strategic relationship that would span the next two decades, with Impaq initially supplying the motor assemblies for Datem’s Neptune range.

Impaq continued to support the modern-day commercial ROV industry as we know it, which largely began on Wednesday, 29 August 1973. More youthful readers may not know the significance of this date so here is a quick summary of events and their repercussions on our industry.

A two-man mini-submarine was being used to bury a transatlantic telephone cable when, what should have been a routine eight-hour dive, turned into a three-day international rescue operation. Having completed the dive the Pisces III was waiting for a towline to be attached to lift it back onto the mother ship when disaster struck. Suddenly the sub fell backwards and began to sink, made worse by an open hatch allowing the aft sphere to fill with water.

The sub hit bottom, almost 500 metres down, impacting at around 40 miles per hour (64 kilometres per hour) and, incredibly, the crew survived the crash only to begin an even more frightening ordeal with more than eight hours of their 72 hours of oxygen already used up.

On the surface other Pisces class mini-subs were being mobilised to effect a rescue and on Friday, 31 August with Pisces II and Pisces V, things were beginning to look good – until further disaster struck. Neither of the two subs were able to successfully attach a recovery line to the stricken Pisces III. Pisces II had to surface when it too took on water leaving Pisces V on the seabed close by to provide some reassurance to the hapless crew.


Fortunately, just like the cavalry in an old western, the US vessel John Cabot appeared on the scene with its CURV-III remote-controlled underwater vehicle. Unfortunately, CURV-III experienced an electrical fault and couldn’t be launched until the next day.

Finally, on Saturday, 1 September both Pisces II and CURV-III were both able to fix lines to the stricken sub and bring pilots Roger Chapman and Roger Mallinson back to the surface with just minutes of oxygen left. And that, was effectively the end of manned submersibles for cable-laying and the birth of the commercial ROV industry.

For the ROV buyer of the early 1980s choice was largely limited to the 25 horsepower Ametek, USA, Scorpio. This prompted Aberdeen, UK-based SubSea Offshore (SSO) to set about designing its own ROV. At 50 horsepower, the Pioneer as it was named, probably went on to be built in more numbers than any other work-class ROV.

SSO produced a design specification and applied the divide and rule principle of sub-contracting the detailed design and manufacture to numerous smaller companies throughout the UK. The hydraulic power unit (HPU) initially combined elements of a Ziehl-Abegg, Germany, motor fitted directly into a bespoke aluminium housing, with a new lightweight aluminium bodied 62cc/rev Rexroth, Germany, A10 series pump. Final development saw the Ziehl-Abegg motor replaced with a more conventional Brook Crompton, UK, stator and rotor. This was the birth of the reliable sea-submersible electric motor. Prior to this, motors were either brushed dc affairs requiring regular maintenance, or borehole pump motors with a very short lifespan when operated horizontally without adequate cooling.

Moving back to present day, virtually every HPU built now follows that basic format. In the early days of subsea HPUs, Rexroth was understandably concerned that its precious pumps were being used in the sea. Today the company probably supplies more hydraulic pumps to this market than all other manufacturers put together. This finally went full circle in 2015 when Rexroth ordered two HPUs for one of its subsea projects, which provided the catalyst for the merging of Datem and Impaq.


For 23 years Impaq had developed the basic HPU principle to establish a reliable range of products now found in subsea applications around the globe with a multitude of operators. During this period the relationship with Datem had grown to the point whereby Datem provided manufacturing and assembly facilities for Impaq.

Following the collaborative working on the Rexroth project, Datem took the opportunity to acquire Impaq Ltd, retaining John Rodgers as its business development manager. Datem is now further developing the existing Impaq range of motors in response to individual client needs, with voltages ranging from 240Vac up to 4160Vac and power outputs up to 400HP.

When Saab Seaeye, UK, was looking for a dedicated HPU with a high power to weight ratio to drive ancillary high power tooling on its Leopard ROV, the company looked no further than the newly merged Datem/Impaq business.

The solution developed for this application combined a unique compact 18.5kW motor specially built to operate at 3000Vac, driving a variable displacement hydraulic pump. Manufactured from anodised high performance aluminium alloy, the motor featured integrated cooling fins and various monitoring sensors with weight saving geometry. This product joins the previous series of hydraulic tooling HPUs used by Saab Seaeye, ranging from 15-30kW.


At the other end of the spectrum, subsea cable laying represents very different demands. When Dutch company Royal IHC was developing its new subsea ploughs, Datem assisted by supplying a number of solutions.

The largest unit combined a bespoke 150HP motor operating at 2800Vac with a Pioneer 21-inch (53.3-centimetre) impellor centrifugal pump, all mounted on a skid. A motor and bell-housing manufactured from marine grade stainless steel was selected for this application for ultimate durability. With a need to operate in both air and sea water, an external cooling system was required. A relatively compact design was still achieved while integrating an oil cooling circulation pump within the motor. To reduce manufacturing lead-time, this motor incorporated Datem’s newly developed cable penetrator.

  • Royal IHC subsea plough

The hydraulics on these ploughs are also driven by Datem HPUs, rated at 18.5kW and operating at 2700Vac. These are more conventional products with a stainless steel casing housing a specially wound stator, coupled with a hydraulic pump. Special effort is made to keep these designs to a compact format for space critical application and to minimise the oil cavity volume.

In addition to the motors, Royal IHC is also benefiting from Datem’s newly developed range of depth pressure compensators, featuring lightweight construction with various sensors.

Following the initial design of the drive motor and gearbox by Impaq for the first Neptune 3000, Datem later bought the rights to the design and started building the motors in-house. With its outstanding durability and reliability, this has been an incredibly successful motor. Based around a four-pole induction motor principle, this motor is driven by Datem’s subsea power inverter to provide 1.5kW of power at variable speeds.

Moving forward, with the combined experience of John Rodgers and Datem’s team of highly motivated professionally qualified engineers, new avenues of development are continually being investigated, within both the subsea motor, HPU and seabed survey market.





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