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how to test a boat speedometer
There are currently three methods:
The first is to use GPS positioning. To put it simply, it is to locate twice in a short time. Divide the position distance of the two times by the time interval to get the speed. This is the ground speed, which is near real time.Buy a GPS Speedometer.
The second is to calculate the ship's speed by using the electromagnetic induction principle of sea water and cutting the magnetic induction line with sea water. The electromagnetic induction intensity generated is actually the voltage. This is the speed of water.
The third is the Doppler principle. The sound wave is sent from the ship. The frequency of the received echo is detected and compared with the frequency of the wave sent, so that the Doppler frequency shift can be obtained, and the ship speed can be obtained. This is also the speed to the ground.
The instrument panel of the ship measures the still water speed, and the actual speed is calculated according to longitude, latitude and route.Knots=1852 m/hWhy does "knots" mean sailing speed? What does "knots" mean? In fact, in the 16th century, the navigation industry was quite developed, but at that time, there was no clock, voyage recorder and other instruments to accurately determine the ship's speed. So a clever sailor came up with a magic idea: throw a rope with a floating body to the sea when the ship is sailing, divide the rope into several sections by knotting on the rope, and calculate the ship's speed according to the number of sections of the rope pulled out in a certain time, so "knots" become the measurement unit of the ship's speed at sea. The speed of sea water velocity, sea wind speed, torpedo and other underwater weapons is also expressed in knots. In fact, the rope node speedometer is not very accurate. With the development of science and technology, the speed measuring instruments of modern seagoing ships can directly display the speed in figures, but knots are still used as the unit for measuring various speeds at sea. The modern precise "knot" means driving 1 nautical mile per hour (1 nautical mile=1852 meters). The mileage of the ship per unit time. Calculated in nautical miles per hour, referred to as knots. It is one of the most important tactical and technical performances of ships. Generally, the surface ship speed measured by log is divided into maximum speed, full speed, cruising speed, economic speed and minimum speed. The speed of large ships such as aircraft carriers and missile destroyers is about 30 knots, while that of small military ships such as missile speedboats and torpedo speedboats is 40 to 60 knots.
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