Wish I never found SN!
Join Date: Jul 2006
Location: Presently in Brisbane, Australia
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Marine radars work by transmitting brief pulses of high-frequency radio waves that are reflected by objects at a distance. The time taken for the pulse to go out and the echo to return is a measure of the distance to the target. The antenna revolves, sending out a searchlight-like beam. The beam has a narrow horizontal spread, in order to be able to distinguish between targets close to one another. It has a broader vertical spread to be able to compensate for rolling and pitching of the boat. The larger the antenna, the narrower the beam.
Radar transmissions travel in a straight line and only bend slightly over the horizon. The visibility of a target is determined by the height of the transmitter and the height of the target above water level. For a radar antenna mounted 25 ft above the water, the horizon is 6.15 nm away. If the superstructure of a ship sticks up above the horizon, the radar will be able to see it further away.
Radar antenna should be mounted where they have a clear all-round view, unobstructed by boat superstructure. Mounting too low will reduce the distance to the radar horizon. Mounting too high may reduce the radar's ability to see close targets. Never mount the antenna in a position where the heads (and eyes) of crew members will be regularly in the line of the radar beam.
Marine radar systems operate in the high radio frequency and microwave range. Unlike X-rays and nuclear radiation the emissions are non-ionising radiation and do not penetrate the human body but can cause heating of the surface, particularly of the skin and eyes (cornea). Measurements taken, in a port, 10 meters from the stationary scanner of a container ship fitted with both a 50 kW set and a 60 kW set, and tests carried out by a manufacturer of radar equipment 10 metres from a 10 kW set with a stationary scanner, have all shown power densities significantly less than danger levels. The examples show that the expected power densities from exposure to ships' radar at a distance of 10 metres are less than 1/100th of the investigation levels even when the scanner is stationary. Marine radars normally operate with a pulsed signal and a rotating scanner, so people are not continuously exposed to radiation even if they are in a fixed position. No link between ill health and exposure to microwaves at levels below the recommendations has been established among microwave communications and radar engineers in the armed services, electronics, broadcasting or communications industries.
I miss my boat
Drinking Rum before 10am makes you a Pirate NOT an alcoholic