In 1956, at the twilight of the golden era of transatlantic liners, the Stockholm and Andrea Doria collided one night in a thick fog off Nantucket Island. Radar, which was then relatively new on commercial ships, gave officers enough confidence to continue steaming through the fog with only a token reduction in speed.

The watch officer on the Andrea Doria had only been tracking the radar blips mentally and was estimating the speed and course of the approaching ships. Unlike his counterpart on the Stockholm, he had not been using a plotting device and when the blip appeared on the screen, he thought the two ships would pass safely apart on parallel courses. At the last moment, when the lights of the Stockholm finally appeared through the fog, the startled captain on the Andrea Doria altered course sharply to port, directly into the path of the oncoming Stockholm.
Soon after the Stockholm/Andrea Doria collision, participants at the International Conference for Safety at Sea in 1960 first addressed the proper use of radar. The result of this and another conference in 1972 was to formally recognize radar as a valid aid to navigation.
 

The diminishing size and amperage drain of radar systems has made their operation possible on boats as small as 25 feet. Unlike professionals on larger ships, however, radar operators on recreational boats are not required to obtain a certificate of proficiency. The danger of using sophisticated equipment without prior training or experience is that a skipper might install a radar system on a boat, turn it on, and go speeding off in a pea-soup fog thinking the screen is going to be his “eyes.” It won’t. Some type of plotting is essential. Radar can also be difficult to interpret, with distortion, clutter, and multiple echoes to confuse the operator. And while radar may be quick to indicate an approaching mass of metal, such as a freighter, it’s not nearly as effective at picking up smaller, fiberglass boats.

Radar is not a substitute for the human lookout. Experience is essential for the proper use and interpretation of information on a radar screen. So is common sense. In the hands of an experienced operator, radar can be used to avoid a collision or negotiate a foggy passage that might otherwise have been impossible. When the operator is inexperienced or careless, however, radar offers little more than a false sense of security. A 42’ sportfisherman, to cite one recent example, was being driven through a pea soup fog at about 18 knots - much too fast for the conditions - on Buzzards Bay, Massachusetts when it struck a 28’ sailboat that was under power (Claim #0348382). Visibility was about 50 feet. The sportsfisherman’s skipper had been watching his radar screen and hadn’t seen anything that would indicate another boat was approaching.
 

In another recent claim, a boat owner on Puget Sound came on watch late one night and wasn’t told that the radar screen had been reset from its usual 16-mile range to a two-mile range. The owner hadn’t bothered to check the setting. The result was that the boat ran hard aground on a ledge and eventually was driven ashore and badly damaged (Claim #98271127).

It should be noted, that the Navigation Rules apply equally to large ships or recreational boats, including Rule 7, which requires that radar, “if fitted and operational,” shall be used properly to determine if risk of collision exits. Proper use includes “radar plotting or equivalent systematic observation of detected objects.” This leaves open the possibility that in a courtroom battle over liability, radar could be the basis for finding fault against you if it was available and not used properly.

Plotting Radar Positions

As with visual sightings, bearings that remain constant while the range is decreasing indicate targets on a radar screen that are on a collision course. Plotting these targets, which is required by the Navigtion Rules, also indicates dangerous course changes being made by approaching boats that would instantly be apparent in clear weather, but are otherwise slow to become apparent on a radar screen.

On early models, plotting involved transferring information from the screen onto a plotting sheet (and marking the time of each observation) to better estimate closing speed. Plotting at least two positions was necessary to estimate the target’s course and speed. Three or more observations were necessary to note a change in relative position.

The next generation of radar, which had television-type screens that didn’t require hoods during the day, meant that a grease pen could be used to mark the positions of other boats directly onto the glass screen. This reduced the time that was required for a navigator to observe changes in the relative position of other boats. Again, at least three observations had to be made for the operator to ascertain any changes.

The newest sets leave a target trail on the screen to indicate an approaching boat’s course. Some new sets also allow you to click on a target - an approaching boat - to get its speed and closest point of approach. These sets are far more user friendly than those of only a decade ago.

Even with the best state-of-the-art set, however, experience is essential to make adjustments for sea conditions and range as well as to interpret information on the screen.

Reprinted with permission from Seaworthy, the BoatU.S. Marine Insurance and Damage Avoidance Report.