Question 826Navigation General

The correct answer is D) the depth underneath the keel against a time base. The recording fathometer, also known as an echo sounder, produces a graphic record of the depth of water underneath the keel of a vessel as it travels. It measures the time it takes for a sound pulse to travel from the vessel to the seafloor and back, and then converts this time into a depth measurement. This depth information is then plotted against a time base, creating a graphic record of the seafloor contour under the vessel's track. The other options are incorrect because: A) the fathometer can measure depths beyond 100 fathoms, B) it does not simply record depth against distance, and C) it records depth, not just the bottom contour.