What is Doppler log speed?
The Doppler speed log is an instrument used to meausure the speed of the vessel or boat. The speed log is based on measurement of the Doppler effect that is, the difference between the acoustic signal transmit by the ship and the receiver return signal after reflection on the bottom of the sea.
How does speed log work?
Speed logs, also known as ship logs, chip logs, or common logs, measure the speed of a vessel. The speed is determined with reference to water flowing by the hull (water reference speed) or to the seabed (ground reference speed).
At what depth Doppler will show speed over ground?
200 meters
Speed through water or speed over ground The Doppler log measures the speed with respect to the surface reflecting the transmitted wave. In deep water the transmitted wave gets reflected by water layer which gets denser as the depth increases. A depth of 200 meters is perfect for the wave to get reflected.
What are the speed log errors?
The transducers should make a perfect angle of 60° with respect to the keel or else the speed indicated will be inaccurate. The frequency generated by the oscillator must be accurate and constant, any deviation in the frequency will result in the speed indicated being in error.
What is the difference between SOG and STW?
Speed Over the Ground (SOG) is the speed of the vessel relative to the surface of the earth. Speed Through Water (STW) is the speed of the vessel relative to the water. It is possible for the STW to be zero while the SOG is 5 knots, for example if the boat was drifting in a 5 knot current.
How do ships measure speed?
These days most ships use GPS to measure the speed of the ship. GPS system consists of a transmitter, receiver and satellite system. This is the most accurate method of measuring the speed of the vessel. Other methods of measuring speed are using doppler shift and correlation velocity log or CVL.
What are the four types of speed log?
Types of speed logs:
- Electromagnetic log.
- Doppler log.
- Impeller log.
- Pito meter log.
- Acoustic Co-relation Log.
Which log should be installed on your vessel to measure Athwartship speed?
dual axis Doppler speed log
Doppler log is an instrument, used in ships, to measure ship’s relative speed with water (in which it is travelling) by the use of Doppler effects on transmitted/reflected sound waves. Display of a dual axis Doppler speed log which shows the vessels movement in the Fore and Aft as well as the Athwartship direction.
What is the difference between STW and SOG?
Which type of speed log is more accurate and commonly used nowadays?
electromagnetic log
Most commonly used however (especially on merchant ships) is the electromagnetic log, more reliable as there is no mechanism subject to breakdown.
Why STW is used for collision avoidance?
Speed over water is only required to be used for collision avoidance and not necessarily for navigation. By using speed over ground, a navigator is more aware of the situation than otherwise. For example, if the ship is drifting towards a danger, navigator will know it better if he has speed over ground in radar.
What is the actual ship speed?
The number of knots passed multiplied by the distance between the knots and divided by 30 seconds told them that 1 knot is equal to 1.852 kilometers per hour or 1 knot is equal to 1 nautical mile per hour. This is how ‘knots’ originated and became a metric system to measure ships speed.
https://www.youtube.com/watch?v=13vTiv1kN2w