What instrument is used to measure depth by lowering a lead and line?

• A. Depth line
• B. Tape measure
• C. Lead line
• D. Sextant

Answer: (C)

Depth sounding with a lead line is how depth is measured on the water. A weighted lead is tied to a line marked at intervals. You lower the lead from the bow until it touches the bottom, and then read the depth from the marks where the line crosses the water surface or rail. The lead line provides a direct measure of how deep the water is at that spot, and historically it’s the standard instrument for this task (sometimes the lead carries a bit of tallow to sample the bottom, which helps identify bottom type but the depth read comes from the line marks).

The other options don’t fit because a depth line isn’t the established term for this instrument, a tape measure isn’t practical for depths encountered at sea, and a sextant measures angles, not the vertical distance to the bottom.