Left: side-scan of a “cloud” of bubbles, created by the propeller of a fast boat; this blocks the side-scan signal completely. The cloud is outlined with a white dotted line. Recorded by Grøn & Jolly in 1994, with a small Knudsen side-scanner. Right upper and lower: the fish mounted on the side of the boat to avoid bubbles from the propeller. The fish is isolated from the hull’s vibrations by a fender. The DGPS antenna is located on an arm, just above the fish, to avoid having to take account of an offset. The “high” antenna is for communication with the base station on land. Photos by Grøn.