Underwater Secondary Propulsion Motor (SPM) Removal

Faced with a submarine suffering catastrophic damage to its secondary propulsion motor (SPM), Shearwater Marine Services devised an innovative underwater solution to remove the SPM while the vessel remained afloat. This approach overcame significant challenges, such as insufficient docking clearance and potential program implications for other platforms. The successful operation exemplifies Shearwater's expertise in submarine diving and their commitment to delivering ingenious solutions in challenging environments.


A client approached Shearwater Marine with a problematic decrease in fluid levels from the internal system of their submarine's SPM. During Shearwater's inspection, the SPM drive motor was found to have sustained irreparable damage, necessitating its removal and posing a series of logistical challenges.


Initial consideration of potential solutions revealed several obstacles. The North platform's docking blocks did not provide enough clearance for the SPM's removal or re-installation. Modifying the dock bottom would involve a lengthy process without guaranteed success. Lastly, docking at Barrow would have significant implications for other platforms in production.


Confronted with these challenges, Shearwater, in collaboration with Babcock’s Submarine Support Engineering (SSE) Group (formerly SSMG), proposed an innovative underwater approach to remove the SPM while the submarine remained afloat. Shearwater provided the concept and design of the SPM Slinging Blank Plate, and SSE Group performed the necessary calculations and drawings to support this idea.

This innovative design created the required clearance for lifting the SPM within the Main Ballast Tank (MBT), allowing the platform to maintain the integrity of the MBT and adjust the trim during daylight hours. This made it possible for the primary maintenance task to proceed as the SPM removal package was conducted during night shifts.

In addition to this, Shearwater tackled several other engineering challenges during this process. They implemented a low-pressure blow system within the port and starboard MBTs for dry hydraulic connection disconnects and blanks, as well as for dry electrical connection disconnects. The platform authorised Shearwater to undertake diving and trimming operations to establish a dry working environment for these work packages. Furthermore, they meticulously calculated the necessary depth for the slinging route and cross-haul, ensuring that the SPM opening did not impede the cross-haul to the SD Angeline. For the encoder cable protection, Shearwater utilised their temporary low-pressure blow system to create a dry working environment within the main ballast tank. This enabled them to apply resin potting to the encoder cable using a Fil-O-Form resin kit.


Through innovative problem-solving and meticulous execution, Shearwater successfully removed the damaged SPM, utilising a low-pressure blow system to create dry working environments within the MBT and meticulous planning to ensure the safety of the entire operation. The client's trust in Shearwater's abilities allowed for the successful completion of this intricate underwater engineering task.


The successful SPM removal operation underscores Shearwater Marine Services' ability to innovate under pressure, navigate complex challenges, and deliver effective solutions. This case study serves as a testament to Shearwater's commitment to tackling unique underwater engineering challenges while maintaining the highest safety and operational standards.

“I would like to express my thanks to Shearwater for their support with this task, not only over the last week but during the planning process. Without their marine engineering expertise and submarine experience, this task would not have been possible.”  - Project Manager Marine (Clyde WSMI)

Find out how Shearwater
Can Support You