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Nautical Terms - page 5

1.5 Navigation Instruments



A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (or points). Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials. When the compass is used, the rose can be aligned with the corresponding geographic directions; for example, the "N" mark on the rose points northward. Compasses often display markings for angles in degrees in addition to (or sometimes instead of) the rose. North corresponds to 0°, and the angles increase clockwise, so east is 90° degrees, south is 180°, and west is 270°. 

speed meter.jpg

Boat speed meter

Since a boat does not have wheels, it can’t measure how fast they’re moving. Instead, your boat speedometer measures the speed of water travelling beneath it. That’s if it’s a more traditional boat speedometer. So there is a small propellor on your boat that is called the impellor log and it, too, measures your boat speed.


Depth meter

The depth meter sends the signal from the transducer at the through-hull fitting to the bottom of the ocean floor. The transducer counts how long the signal takes to go there and bounce back, does some fancy math, and spits out the answer.


Wind speed - Indicator meter

An anemometer is an instrument that measures wind speed and wind pressure. As the wind blows, the cups rotate, making the rod spin. The stronger the wind blows, the faster the rod spins. The anemometer counts the number of rotations, or turns, which is used to calculate wind speed. That devise is connected to an electronic circuit that gives an instant readout of the wind speed on a digital display.

The weather vane points toward the source of the wind because the balancing weight is at the point of the arrow. The surface area toward the back of the arrow is lighter, and therefore catches the breeze, and turns to distribute the air flow evenly on both sides of the arrow.


Auto pilot

Autopilots and other self-steering systems are simply devices and processes that generally provide a means to set the course of a boat on a particular heading or wind direction, and then provide feedback to mechanisms that control the direction of the boat should the steering be required. These days, the most commonly seen systems use a fluxgate (electronic) compass that detects the current heading of the boat and compares it with the heading that has been set by the operator, and directs mechanical systems to change the rudder position to bring the boat to the pre-set heading.

Basically, you put the boat on the heading you want, hit a button (usually creatively named “Auto”) and the boat stays on that heading as long as it is moving at sufficient speed for the rudder to steer the boat. More advanced autopilots also can be set to steer to the wind (assuming you also have wind instruments), and most have a means of connecting them to chartplotters to make the boat steer a course.


GPS Chartplotter

A Chartplotter is a device used in marine navigation that integrates GPS data with an electronic navigational chart (ENC). The chartplotter displays the ENC along with the position, heading and speed of the ship, and may display additional information from radar, automatic information systems (AIS) or other sensors. As appropriate to particular marine applications, chartplotters may also display data from other sensors, such as echolocators or sonar. Electronic chartplotters are by nature CPU (and GPU) intensive applications. Chartplotters need to retrieve the Navigation Signal (Galileo, GPS, GLONASS, WAAS etc.) and overlay that on a map. Map updates on dedicated hardware typically have screen refresh rates from 5 Hz to 30 Hz.


Marine radar

Marine Radar - Radio Detection and Ranging, is used to detect objects and their position relative to your current location. It works by sending out a radio signal. It does so by detecting other ships and land obstacles, to give bearing and distance for collision avoidance and navigation while on water.

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