Studies at sea on the Reson Seabat 7150 & 7111 multibeam echosounders aboard RV Pourquoi pas?, to evaluate: - developments and solutions for defects (bathymetric artifact 7111; multi-ping bias 7150 ; "ghost reliefs") and functions noted to be lacking at the previous SAT cruise (autopilot); improved performances thanks to new Bottom Detect algorithm; echosounder performances with respect to contractual specifications at the outcome of all modifications, following a similar procedure to that for acceptance sea trials in January 2007, December 2007 and July 2008. Trials will be conducted on several dedicated zones: The Seabat 7111 (100 kHz) echosounder will be tested in the Iroise Sea and the Bay of Douarnenez; the performances of the Seabat 7150 (12 and 24 kHz) will be assessed on the slope, the Meriadzek Terrace and the adjoining deep seafloors. The cruise fell under the 'RV Pourquoi-Pas? facilities' programme.