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Marine - Shipboard Underwater Log / Speed Log Equipment


The Underwater Log Equipment measures and indicates the speed of the vessel and its distance traveled through the water. It also transmits this data electrically to the various shipboard navigation, sonar, fire control and weapons systems as required.

Types of Underwater Logs:

Electromagnetic Log

The Electromagnetic Log operates on the principle of an electromagnetic field and electromagnetic induction.

Major components:

marine shipboard underwater log - speed log systemsSea Value - Mounted in the hull of the ship, the sea value and packing assembly provides a watertight support for the Rodmeter. It also functions to seal the hull of the ship when the rodmeter is removed for maintenance.

Rodmeter - The rodmeter provides an AC signal that is proportional to the ship’s speed. The rodmeter or “SWORD” as it is sometimes called is easy to identify. It looks like a long sword hence its name. The sensing unit of the rodmeter is contained in the “BOOT” at its lower end. An electromagnetic field is used to detect changes in the ship’s speed by electromagnetic induction.

Indicator – Transmitter (I/T) - The Indicator – Transmitter displays the ship’s speed on a dial and the distance traveled on a counter. The primary internal components of the I/T are the speed servo, the integrator and the distance servo. The I/T has output synchros that transmit ship’s speed and distance information to ship’s systems throughout the ship.

Electromagnetic Voltage Simulator (ELVS) - The Electromagnetic Voltage Simulator (UL-1000) is a piece of test equipment designed to simulate the voltage produced by the rodmeter to test and troubleshoot the ship’s speed log indicator – Transmitter independent of the Rodmeter. The ELVS is supplied with a variety of connector – cables so that it may be used with the majority of I/T types.

Model Examples:
marine electromagnetic speed log - rodmeterLitton Log Equipment
Control Instrument Log Equipment
Gould – Chesapeake instrument
Mk4 mod 1&2
McKiernan – Terry
Mk5 mod 1
Mk 6 mod 0,1&2

Equipment Manufactured By:
Control Instrument
Gould – Chesapeake
McKiernan – Terry