🔍 Key Concepts

• What a recording fathometer measures (echo-sounder function) • Difference between time base and distance base on a chart or strip record • How the bottom contour is shown over the vessel’s track

💭 Think About

• Is the instrument primarily used to know how much water is under you at this instant, or to build a picture of the sea bottom along your track? • Would the horizontal axis of the graphic record logically represent time as the ship steams ahead, or distance traveled along the bottom? • Does a practical navigation/depth survey tool usually limit its usefulness to a fixed maximum depth like 100 fathoms?

✅ Before You Answer

• Clarify whether depth below keel is commonly what’s displayed, or depth of water below the transducer at the hull • Decide if a graphic record used for surveying and piloting is more useful against time or distance as the horizontal scale • Check whether it makes sense for a standard recording fathometer to show only ‘bottom contour’ without explicitly relating it to depth vs. distance or having an arbitrary depth limit