Thoughts about Radar:
A radome mounted 20 ft above the water, providing the range is equal to or greater than 16 nautical miles, will have a target range of 16 nautical miles under ideal conditions, assuming the average target height is 50 ft above the water - from range calculations under ideal conditions.
Based on cell resolution calculations, at a 2 nautical mile range, the resolution of an 18" array is 28% greater than a 12" array. Two targets 1,000 yards apart and perpendicular to the radar beam's path, will be detected as 2 separate targets by the 18" array and one target by the 12" array. The width of the beam for an 18" array at 2 nautical miles is 950 yards, whereas for a 12" array, the beam width is 1,320 yards, i.e. an 18" array can resolve targets that are greater than 950 yards apart and a 12" array can resolve targets that are greater than 1,320 yards apart. These calculations assume, targets are abreast of each other, perpendicular to the beams path and the plane of the radar resolution cell, defined by the beams width and height, crosses both targets at the same time.
Reports and calculations have they place but for the average sailor, the limiting factor is the size of the display. Most displays on sailboats have 6" or 7" screens. In-shore, we observed the targets are too small at a range setting of 8 nautical miles. A range of 4 nautical miles or less is more practical on the smaller screens. Off-shore a range setting of 8 nautical miles appears to be practical with respect the size of the targets displayed on the screen. Based on my observations of the radar screens on tug boats, a ship I worked and IDUNA's 6" LCD radar screen, I came to the conclusion the size of the radome (range) was not as important as the size of the display screen. The larger the display screen, regardless of the radar's specified range, the better the unit becomes as a navigation tool.
IDUNA's radar unit is a Furuno Model 1622 - 15" array, 16 nautical mile range, 6" LCD screen with VRM, EBL, track trace, guard range setting, sleep mode, etc. This model is Furuno's base unit and was selected based on, cost, small radome, "low" amps, small LCD display unit and the fact most commercial vessels are fitted with Furuno navigation equipment. Our GPS system is manufactured by Furuno and is the same unit used on many of the tugs I worked aboard.
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I had another opportunity to speed with one of the largest firms in the Bay Area regarding their preferences of Radar/chartplotters on the market and what the consumer should expect.
Their response is the RayMarine units for the average consumer are easier to bring online, more intuitive, less manual time, work well.