The distance traveled by the ship can then be calculated from the speed.
Electromagnetic logs indicate water speed. Sensors in the ship hull use Fleming's rule.
There are two types of sensors (fore-and-aft) and dual-axis sensors (fore-and-aft andstarboard-and-port). In addition, various types of sea valves are available for installing sensors on the bottom of the hull. The sensor head extruded from the bottom is either 7mm or 50mm long type.
EML500: This type is suitable for general merchant vessels, and accepts both flush-mountable and dual-axis sensors.
EML50: This type is compact and can be mounted in many different ways.