How were depth determination made before the invention of sonar?
This is a really great question! Before the invention of sonar, Early mariners made depth measurements, called “soundings”, using a hemp rope marked in equal distances (usually “fathoms” which was the length of a person’s fully outstretched hands, or 6 feet). With a lead ball on the end, the mariners would lower the rope until the tension in the rope changes, indicating that the lead ball had reached the bottom. If the covered the ball with grease before the let out the line, they could pick up sediment from the ocean’s bottom (which would stick to the grease). This would be another indication that they had hit the bottom, as well as a way to sample what kind of terrain is underneath them. This method worked fine for shallow waters, but in deeper waters it was too difficult to tell when the ball reached the bottom, because the hemp line was so heavy. Later, piano wire with a connonball attached to the end was used in deep water. The greater difference in weight between the line and the
