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Radar stand for radio detection and ranging.It is the most important  for navigation.This system is devolped during the Second world war. Today the microwave radio frequencies are more used than shortwave frequencies because their short wavelenghts allow them to be directed in narrow beams.
FEATURES:
The radar uses electromagnetic waves to investigate the presence of object around the ship.The waves are broadcast, all around the ship, by a rotating antenna. The antenna emitting a series of very short repeated pulses of microwave energy. When the beams of microwave energy strike a solid object, part of that energy is reflected back to its source.This reflection is picked up by the radar antenna and through this echo we know the distance of the target. The radar screen is called PPI (plain position indicator). it gives a representation of the area around the ship. in this screen the position of the ship shows at the center of the screen. The flourescent point on the screen represent the position of target and by means the buttons the officer can adapt the view of targets based on the condition of the weather and the sea. the maximum range is usually less than 20 miles. The officer can choose different layout that are: brilliance,gain,tuning,
clutter; different orientation:north-uo,course-up,head-up;different target movements:true motion and relative motion; different data source:ground-stablished or water-stablished

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The ARPA allows us to acquire each target and perform its tracking.The traqcking allows to know the relative and absolute course and speed of the target and its CPA (closet point of approac) and TCPA (time to closet point of approach). The most function of ARPA is the trial manouvre by which any change in the own course and speed can be tested before application.

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Measures the UKC (under keel clearance) that is the height betweeen the bottom of the ship and the seabed.
FEATURES:
It is based on the reflection of waves sent downwards by a transducer installed on the hull. The   last that the signal employsfor to return is proportional to the height of the water .

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AIS is an instrument that gives other additional information of the radar data. It trasmits via some VHF channels. the AIS is very important for communication a secuity purpose. It produces stronger signals and allows for the recognition of targets in advance. The data trasmitted by the AIS are: static information, voyage related information and dynamic information.