Adventurers Roy Karlfen and Ove Herlogsen during their circumnavigation of the globe in an 18-foot Uttern (means Otter in Swedish). Pertinent to the theme of this story, notice the radome on top of the arch.

No doubt you've noticed today's radar sets are compact and relatively inexpensive. Those qualities make them ideal candidates for installation on small boats.

With that preface in mind we present the basics of choosing and using a small boat radar system. Before deciding which model might be best suited for your small boat, first consider how you might actually use the radar.

Radar is an aid to navigation, a tool that helps us avoid collision with other vessels and landmasses. But that's not its only function. For example, some mariners rely on it to penetrate fog or heavy weather. But in order to do that, you'll need one of the more powerful units. Conversely, if you only want something for nighttime navigation in clear atmosphere, then a smaller 1.5 or 2kW unit would be adequate.

You should also know offshore fisherman regularly rely on radar to spot birds and, therefore, where the fish are. For this application, higher power units matched to the appropriate antenna are required.

This brings us to the discussion of resolution. The narrower the signal beam width, the higher the resolution. To boost the resolution, there also needs to be a corresponding boost in the power of the unit. Higher resolution models cost more than basic units.

Typically, small boat radars transmit a signal between 1.5 and 4.0 kW. With the greater power, you are able to see smaller or weaker targets that do not have a good radar cross-section. In other words, higher output can spell the difference between being able to spot a little bird or a ship at sea.

For basic navigation, where you are simply looking for landmarks and other large objects, a lower power unit might work the best. To cut costs to the bone, a monochromatic screen displays the same information as the more expensive color displays.

In selecting the radar display screen/ lighting conditions on deck should be considered. Generally the monochrome LCDs are easier to see in bright sunlight. Another significant benefit: they're easier for the manufacturer to waterproof, which in turn can mean a longer service life.

The more expensive CRT (cathode ray tube) displays echo well and at wider viewing angles than an LCD, except in bright sunlight. Color displays, especially the color TFT, work particularly well in all lighting conditions, even the brightest sunlight.

Most mariners, after seeing the difference between the monochrome and color displays opt for the color. Another plus in favor of color, in the higher power units the color density provides a better clue about the weather ahead. Fast boats use radar to watch thunderstorms, find a hole and plan an alternate route.

As we mentioned earlier in the story, the power rating (measured in kW) is a critical factor in determining overall capability. But just as important as the power rating is the type of antenna and its mounting height relative to the waterline.

Antenna width determines the ability to separate objects in close proximity to one anotl1er, in other words, whether a blip on the screen represents two ships or one.

The term radome describes an enclosed radar antenna as narrow as 18 inches in diameter. An 18inch radome matched to an entry-level radar antenna has a range of about 16 nautical miles (nm), whereas a slightly larger radome, say 24 inches, has a range of 24 nm.

One disadvantage of the radome is that its characteristically narrow antenna results in a wider bandwidth. As a consequence, targets clump together. However, on the plus side of the balance sheet, radomes are somewhat less expensive than the larger open array antennas.

Unfortunately, when approaching a bridge, the reflected image of the span and supports will show up on the display screen as one solid mass. So in the dark or in heavy rain or fog, you'll still have to visually spot the channel between the pilings.

Open array antennas are exposed to the elements so their rotating element can be plainly seen. Because they can be as broad as 72 inches, beam width is reduced. As a result, the discrimination of targets is dramatically increased. At the higher power levels, open array antennas can reach out to 72 nm.

You should also know that effective range is limited, no matter what the kW rating, to the height of the antenna. Generally, the higher the mounting, the more distant the range. In other words proper mounting allows a radar set to actually reach its optimal range.

You should also know recreational mariners typically operate their radar sets at close range, usually within about a four-mile radius of their boats. Utilized in this manner, radar establishes a comfort zone so you can determine which targets are approaching and which are steaming away.

The built-in guard zone features sounds an audio alarm when radar detects an approaching vessel. It works while underway or when anchored. The VRM mode, short for variable range marker, allows measuring range to a moving target or a landmass.

Long-range settings are more appropriate for foul weather detection or to signal an approaching landfall at the end of a passage.

Another tantalizing consideration: radar can be linked to GPS so critical navigation information can overplayed onto the radar display, giving the helmsman a clearer picture of the land formations close at hand. Radar also talks to chart plotters, which means the echoes be overplayed onto a chart. Another key feature, waypoints can be displayed on the screen.

This gives rise to the salient question: Do you plan on adding chartterplotters, GPS and other electronic gear? If so, wou1d you like the new components to be the same brand on your radar?

Once the radar set is installed, practice with it in order to develop skills necessary to adjust for rain clutter and other environmental effects. For example rain and snow both create a multitude of small echoes that continually change in size and position. Adjusting to make the unwanted echoes disappear leaves real targets visible. That is unless you're too heavy handed and the adjustment cancels out channel markers and other targets.

In order to become really proficient with radar, it's wise to enroll in a hands on course. If you don't want to attend in person, there are software packages available for home study. Besides the raw information, graphics files show you what to look for.

In your studies you'll learn how an overhead cable crossing can mimic a moving target on your radar screen and how the mass or right angles in a bridge structure can cause strange patterns of interference on your screen. In addition, you'll learn how current can affect a buoys echo. Going against the current, buoys lean in your direction and produce a stronger image. Conversely, while going with the current, channel markers appear faint.

Also important to keep in mind is Rule 5 from COLRECs (collision regulations):