The objective of the new survey for Bannerman Ltd, operators of Invergordon's Admiralty Pier, was to ascertain the depth alongside the pier and to check for any hazards that could affect the safety of the berthing. The imminent arrival of QM2 meant the preliminary findings had to be reported to the client and the port authority immediately upon completion of work.

Based on his previous experience at the site, Fathom's chief surveyor Chris Harper chose to use a Reson SeaBat 8124 multibeam system integrated with an IXSEA Octans 3000 motion sensor and gyrocompass into an online system. For speed of sound measurements, a Valeport 650 sound velocity probe was used and for positioning, a Trimble AG132 DGPS was employed utilising differential corrections from the IALA beacon broadcast network.

The DGPS system was checked against a previously established control station and was shown to be within 1.5m.

For the earlier pre-dredging survey, fathoms had used the port authority's own survey vessel.

On this occasion, it chose to use its own survey catamaran Elliann , which has a moonpool through which multibeam sounders and other systems can be installed.

With just three days to go before the arrival of QM2 , Elliann was quickly mobilised and the survey began. The gyrocompass alignment was established using a RegElta Total Station at a known point and reference object onshore.

The vessel's heading was then calculated by observing angles and distances to the bow and stern while simultaneously recording the gyro's output.

A patch test calibrated the SeaBat 8124.

For the survey programme, lines were run parallel to the Admiralty Pier jetty and extended out past the dolphins to the west and east. The online QPS QINSy software was used to ensure there was sufficient overlap of the lines and that adjacent lines were observed at the shallowest depths.

Additional lines were then run along the jetty to saturate the critical area of the berth with redundant observation.

Online quality control was provided by the QPS QINSy software suite.

By the end of the day, the entire berthing area and its approaches had been surveyed.

Fathoms processed the data with the industry standard CARIS HIPS package and all observations were then merged, edited and gridded.

Nearly 70,000 soundings had been collected and these were used to derive a high resolution 3D colour representation of the seabed. For the final chart, the Cromarty Port Authority's database provided a WGS84 rectified Ordinance Survey plan that was overlaid on the bathymetry.

The results of the survey were a relief to the clients, showing as they did that there was sufficient water for berthing the QM2 with room to spare and that the seabed was free of hazards. Two days later, the giant ship arrived at Invergordon and tied up at Admiralty Quay, its passengers unaware of the small survey boat that had so recently ensured their safety.

MJ Information No: 21136