How does it measure athwartships speed?

In addition to measuring the ship’s speed over ground and speed through water, some Doppler logs have the unique ability to provide the athwartship speed over ground.

This means that the log can measure the ship’s sideways velocity with respect to the fixed ground, which is useful in situations where the ship needs to make lateral movements such as in docking, navigating through narrow channels, or avoiding other vessels.

Dual-axis Doppler logs are employed to measure the athwartship speed over ground. These logs have additional transducers that are oriented in a horizontal direction and measure the Doppler shift of sound waves reflected off the seabed or water layer in a transverse direction.

By analyzing the Doppler shifts in both the longitudinal and transverse directions, the log can calculate the ship’s speed over ground in both longitudinal and transverse directions, allowing for precise navigation in confined waters.


The introduction of Doppler log has brought about a significant change in the approach of Masters and officers at sea. The ability to accurately measure ship’s speed and drift allows navigators to make more informed decisions while maneuvering, leading to increased safety of navigation.

The use of Doppler log has also eliminated the need for traditional logs such as the chip log, which required throwing a log overboard and measuring its drift, saving time and increasing efficiency.

If all ships were equipped with an operational Doppler log, it would significantly improve the safety of navigation and reduce the risk of accidents at sea.

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