“An alternative is the American-built FarSounder, which gives you a sonar picture of the seabed up to 1,000 metres ahead. Fitted to the mothership, it is a six-figure investment and the boat needs to be hauled out for installation, but it works at speeds of 20 to 25 knots. “Our systems are designed to map the sea floor in 3D out to a range of at least eight times the depth of water below the transducer module,” says Matt Zimmerman, Farsounder’s executive vice-president of engineering. “However, even in shallow water, they can detect in-water obstacles out to the full range of the sonar. We have had a number of customers report that they can see large whales with the sonar.”