Shoal Draught Handrail Technique

Definition

Rather than aiming at a mark, the navigator steers to keep the echo sounder reading within a band, for instance holding between 8 and 12 metres to parallel a coast clear of an offshore shoal. Because the sounder gives a continuous independent measurement, it cross-checks GNSS and remains valid if position fixing fails. It works best where contours run roughly parallel to the track and the seabed slopes steadily rather than in steps.