Marine Glossary

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maximum range

From a practical point of view this is the highest range selectable on the face of the unit. If you cannot set the unit to anything higher than 32 nm, then that makes a reasonable defintion of maximum range. On the other hand, the height of the antenna also limits how far the radar beam travels before hitting the surface of the water. This range is about 1.2 x square root of the antenna height in feet. At 25 feet high, this "geographic range" is 1.2 x 5 = 6 nm. Targets beyond that distance will be seen only if they reach above their own geographic range--if we may put it that way. For example, if the target is 16 feet tall, then its geographic range is 1.2 x 4 = 4.8 nm. Therefore if a target is located 10.4 nm from you, it must be at least 16 feet tall to be seen. In practice it has to be rather taller than that so it can project some reasonable area above the horizon. Shorter than that it will not be seen at that distance off no matter how big it is, or what it is made of.