Pitometer log

[1] This nomenclature dates back to days of sail when sailors tossed a log attached to rope knotted at regular intervals off the stern of a ship.

During World War II, pitometer logs were often interfaced directly into warship fire control systems.

This interface was necessary to allow gunnery and torpedo fire control systems to automatically track targets.

In early realizations of the pitometer log, mercury manometers [3] were used to measure the pressure differences (see Figure 1).

Equation 2 can be solved for the velocity of water in terms of the difference in pressure between the two legs of the manometer.

Figure 1: Photo of World War II US Navy submarine pitometer. This unit uses a mercury-based manometer to measure the difference in static and dynamic water pressure.
Figure 2: Illustration of a Mercury Manometer-Based Pitometer Log.