Consultants JP Kenny Ltd needed to define an area with suitable water depths and geotechnical characteristics for the location of a Single Point Mooring (SPM) for tankers and to provide information on the seabed topography and soil conditions for the excavation of a pipeline trench. This required the acquisition of bathymetric, geophysical and geotechnical data.

The marine survey covered a 7km by 1km offshore corridor for the pipeline, a 2km 2area for the SPM and a large tanker turning area. In all, an area of around 36km 2was surveyed.

For the offshore section, Andrews equipped two local vessels, the Hope for hydrographic work close to shore and the Courage for the deeper areas and geotechnical operations. Equipment was shipped both by air and in two 40' containers by sea from the UK. This enabled the Courage to be mobilised in neighbouring Togo and fitted with all necessary equipment for working offshore in Ghana. Survey lines were required at 50m grid intervals.

Positioning was achieved using Andrews mobile RTK GPS systems with RTK control established by Andrews geodetic surveyors.

The coast of the Gulf of Guinea is littered with shipwrecks. The scope of works thus required a near-surface geophysical survey using sidescan and magnetometers to identify seabed hazard features and obstructions. Sub-bottom profiling provided sub-surface details to a depth of 10m. In addition, vibracores and grab samples were obtained to determine seabed soil condition, some of which were subject to onboard tests for sulphate reducing bacteria.

In addition to the fieldwork, Andrews also completed laboratory testing and detailed interpretation and charting at its Great Yarmouth UK base.

MJ Information No: 16605