Speed over ground and Speed Through Water (Video Lesson)

The difference between speed through water and speed through ground is as follows:

  1. Speed through water (STW): It is the speed of a vessel in relation to the water in which it is moving. It is measured by instruments such as paddle wheel logs, pitot tubes, and Doppler logs. STW is important for navigational purposes as it determines the time of arrival at a destination and the amount of fuel required to cover a certain distance.

  2. Speed over ground (SOG): It is the speed of a vessel in relation to a fixed point on the Earth’s surface, usually measured by GPS or LORAN-C. SOG takes into account the effect of currents, wind, and other environmental factors on the vessel’s movement. It is the actual speed at which a vessel is moving and is important for determining the vessel’s position and course.

The main differences between STW and SOG are:

  1. Currents: STW is affected by the currents of water in which the vessel is moving, whereas SOG takes into account the effect of ocean currents on the vessel’s movement.

  2. Wind: STW is affected by the wind’s effect on the water, whereas SOG takes into account the wind’s effect on the vessel’s movement.

  3. Navigation: STW is important for navigational purposes, such as determining the time of arrival at a destination and fuel consumption. SOG is important for determining the vessel’s actual speed and position.

    Video Lesson :

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