Marine Radar

Once within reach of only the most affluent boaters, marine radar has enjoyed increased popularity due to lower prices, improved designs, and the relatively recent ability to interface with other navigation instruments such as GPS chartplotters and autopilots. Anyone who has found themselves trying to navigate through dense fog or pick out navigation lights against the cluttered background lights ashore can appreciate the additional safety factor that marine radar brings to coastal and offshore navigation. Whether interfaced with other navigation instruments or not, radar is a powerful navigation device that can be used in any situation.
How Radar Works
Radar systems are made up of a display and a revolving antenna (or scanner). A stream of short pulse radio waves are transmitted through the antenna and a computer inside the radar receiver measures the time delay of the echo received and calculates the distance to an object or landmass while the rotating scanner determines the bearing. The results are then displayed on the radar screen.
Navigating with Radar
Boaters equipped with radar can more confidently expand their cruising grounds without feeling completely at the mercy of darkness or the sudden approach of squalls. Radar allows boaters to see landmasses, other vessels, or navigational aids which might ordinarily be hidden from view by darkness or weather conditions. While rain and other precipitation considerably shorten it’s effective operational range, this sensitivity to precipitation also tends to make radar a useful detector of approaching bad weather.
Most users operate radar in the Relative Presentation/Heading Up mode because it's the easiest to interpret at a glance. This means that the top of the display screen is always oriented with the bow of the boat, and targets on the screen are always relative to the vessel’s heading.

Another display mode, True Presentation/North Up is oriented like a chart with the boat in the center and the top of the screen pointing north. This makes it possible to observe how navigation aids move on the screen as the boat remains on its intended track. Radars with a north-up mode are usually interfaced with an electronic compass.

The latest and most versatile option is the Course Up mode, which receives navigation input from a GPS or Loran and/or an autopilot (optional). With this mode the top of the screen is relative to the rhumb line course of a selected waypoint. If the heading line of the boat drifts off the rhumb line from either pilot error or current, the resulting movement will show the XTE (cross track error), which can then be easily corrected. This mode is also ideal for avoiding collisions.

Selection Tips
Display Type
Radars are currently available with monochrome CRT, monochrome LCD, or color TFT displays. Legibility under all light conditions is the key factor in determining the best display for a particular boat. Boat size and radar location will greatly influence whether you choose a lightweight LCD display or a larger, heavier, high-resolution CRT display. LCDs are most common in cockpits and on flybridges because they show up well in sunlight, are easily disconnected and stored below, and some are waterproof. Monochrome CRTs will show better definition out of direct sunlight, but are best permanently mounted below or in an enclosed cabinet on the flybridge. However, with incredible visibility and dropping prices, the newer color TFT displays are now dominating the market.
Transmit Power
Small marine radars transmit between 2-6kW of energy, with transmit power determining the strength of the signal sent by the antenna and the corresponding echo back--the stronger the transmitter, the more likely soft or distant targets will show up on the screen. Transmit power is more important in poor weather, since fog, rain, and drizzle tend to absorb the energy and reduce radar range. Antenna height is also a factor because radar is a line-of-sight system.
Open or closed array antenna?
As a rule, the larger the antenna, the better its chances of distinguishing separate objects that are close together in congested areas. Open arrays are generally larger and found on powerboats. Closed arrays, called radomes, are usually reserved for sailboats where protection from sails and rigging is a concern.
Where to Buy
To determine the best choice of marine radar for your boat, it’s often a good idea to talk to a knowledgeable marine electronics specialist like those at MarineTech North America. They can explain the features and capabilities of a particular marine radar model and offer suggestions based on boating style and budget. MarineTechNA offers an extensive selection of marine radars and accessories. They also have a wide variety of other marine electronics such as GPS chartplotters, autopilots, fishfinders, and more