A system for monitoring a twin trawl being towed by a vessel, the twin trawl comprising two trawl bags, two trawl doors and a clump, comprises at least one sensor arrangement for measuring distance between the doors and between one door and the clump, and a processing unit for computing geometric indicators based on the measured values. By means of the transmission of acoustic signals, the distances between the doors and the doors and the clump can be calculated and compared, and thus provide geometric indicators.
