As kids we all thought that echoes were fun and interesting but did you know you could use them in piloting? Note the time in seconds from a signal to the return echo from a cliff, iceberg, wharf, or moored freighter. Every second’s delay indicates a distance off of 1 cable, or 200 yards. Every 10 second’s delay indicates a distance off of 1 mile.
This rule could be useful in fog some day. A blank pistol shot produces a sharp echo, but the ship’s bell or horn will work as well. Even a loud hailer works in close quarters. The Rule of Thumb at work here is that sound travels about 1 mile in 5 seconds.