Pivoting Sonar Support Arm

We were approached by Gordon Campbell of Aspect Surveys to help design and manufacture a Pivoting Sonar Support Arm.  This was to give them the facility to lower a Sonar unit off the side of their Survey vessel "Vigilance".

The system is primarily to deploy a multibeam sonar  but is capable of housing a variety of different sensors if required. When deployed the sensor is 1m below sea level, but the pivot mechanism raises it to deck level when not surveying to allow maintenance and or easy removal. The system smoothly and easily pivots through 90° with a system to secure the arm and sonar bracket to the side of the boat.

of the challenges we faced was the need for the pivoting arm to operate in heavy seas when lateral and longitudinal forces could be very significant.  Subsequently, the whole sonar arm + pivoting mechanism was substantially engineered, rigidly mounted to the vessel structure and manufactured from marine grade stainless steel including the bearings and pivot shaft.

The other challenge we faced was that the bracket needed to be extremely stable during survey operations at up to 7 knots to avoid degradation of the quality of the sonar data.  Motion of the vessel is measured up to 50 times a second in all axes to correct the sonar data so any difference in motion characteristics between the position of the motion sensor and the sonar causes data to rapidly become unusable, thereby limiting the vessel’s operating window.  This issue was mitigated by creating a receiver pocket which was fitted to the hull of the boat to support the system close to the waterline.  The sonar arm was fitted with a receiver pin and the whole arm was mounted on linear slides and a hydraulic piston which allowed the arm to be lifted and dropped into position within the receiver pocket.

This work was all carried out on board the boat whilst it was docked within Ardrossan Marina and the boat is expected to be going straight to work on a marine renewable survey contract.