Radar Reflectors

Sometimes it pays to be a pumped-up loudmouth.

The famously thick fog in my Maine home waters is the classroom for many tutorials in marine safety. I've lived my share of those lessons, and one even left me grinning. On that particular August afternoon, I was at the wheel of an unfamiliar but well-equipped and lovely 50-foot schooner, bound from Camden with a party of inexperienced sailors. The boat's radar was inconveniently far below at the nav station, but I'd had a peek before we slipped into the pea soup and knew that a number of vessels were gathered around the entrance bell buoy. It was nearly calm, and folks in these waters tend to take it slow and careful, so I wasn't overly anxious.

I did, however, engage the boat's foghorn. It was an unusually large model driven by compressed air, and darn if it didn't emit a powerful "blooooooooooonk" that made us sound like a tramp steamer. And darn if our unseen neighbors didn't whip into action. We could hear powerboats clink into neutral and winches grind as sailboats changed course. The fleet parted before us like the sea before Moses. I quite liked that, and have henceforth valued the concept of sounding (and looking) large.

The lesson is relevant to the more dangerous world of passagemaking. If you are in the vicinity of big ships traveling at speed in dark or fog, a big horn is not going to cut it. What you want is to paint a significant target on everyone's radar screens, and the sooner the better. When delivering yachts, I spent many a nervous watch passing through shipping lanes and amongst fishing fleets, wondering just how good a radar signature I was making. Sometimes I asked other vessels, and the results weren't always encouraging.

Wooden and fiberglass sailboats know they have a radar problem, and most are equipped with one of the various passive reflectors, which are essentially geometric shapes that put as many perpendicular metal surfaces around the horizon as possible. Unfortunately, they don't work very well, as was thoroughly documented by a U.S. Sailing Association testing program several years ago. Powerboaters tend to think that their vessels are substantial enough to reflect back a reasonable amount of radar pings, and often they're right; a lot of vessels sport enough metal hardware and internal machinery to do a fair job. There's also the half-truth that if you are running a radar yourself it will generate a signature. The whole truth is that sometimes one radar will pick up interference from another's pulse; but a radar's interference rejection (IR) filters remove that interference, and most operators use IR in busy traffic.

Times are also changing. Boats and ships are faster, and there are more of them out there. Bridges are more lightly manned making the use of radar more critical for collision avoidance. Modern automated radar tracking usually won't lock onto a target unless it appears in at least half its sweeps. The bottom line: I'm not satisfied to even look my size when in traffic with ships that are galloping elephants compared to my 50-foot mouse. Humble as I fancy myself, I want to swagger onto the radar screen of a ULCC (ultra large crude carrier).

It turns out the International Marine Organization (IMO) shares my sentiments. In its safety requirements for international commercial (SOLAS) vessels, the IMO requires boats under 150 gross tons to carry a reflector that meets certain standards of what's called Radar Cross Section (RCS).

To measure RCS, radar echo measurement equipment is calibrated to a precision steel sphere. Then a reflector is tested from every angle around the horizon, resulting in a plot of effective RCS in the form of an irregular circle. (The classic cornered radar reflector generates flower pedal plots.) The IMO requires a mandated vessel to show a 10-square-meter RCS area from at least some angles and a minimum of 2.5 square meters everywhere else. Amazingly, only one passive reflector currently meets this standard, the Cyclops 3. Within its 10"Hx17"Wx18"L fiberglass case, the Cyclops has "di-electric lenses" capable of refocusing and returning radar pings. The technology was invented by the British Ministry of Defense and during the Falklands war was hung beneath helicopters and worked well enough to lure radar-guided Exocet missiles away from their targets.

Given British weather and Channel traffic, it's no surprise that another innovative radar reflector also comes from the U.K. The Sea-me radar target enhancer, produced by a small company of the same name, sells in the same $500-to-$600 range as the Cyclops 3, but looks and works quite differently. Proprietor Peter Munro was an early-retired aerospace engineer when a heart-stopping 150-foot close call with a coaster off the island of Jersey in fog "inspired" him. He chose an "active" technique, in which a receiver listens for incoming radar pulses, amplifies them, and sends them back out. The technology is not new, but Munro's goal was to improve the level of performance versus size and price. He feels he has achieved this goal with the Sea-me.

The Sea-me has been tested at 63-square-meter maximum RCS with no point showing less than 10 square meters, easily exceeding the IMO's present requirements for passive reflectors. Real world users quoted on Sea-me's Web site report noticeable effects, like being seen at 12 miles even in wave-cluttered seas. Another feature is the red "activate" light on its control box, which will provide a head's up if traffic enters a radar-quiet part of the ocean. The Sea-me is not perfect. Though installing its 18"x2" antenna wand on a powerboat should be trivial, I'd be inclined to paint over its rather emphatic branding beforehand. More importantly, Sea-me only works with X-band radar. X-band is far and away the most common type of radar, and all SOLAS ships are required to carry it, but many also carry an S-band set, which they tend to use more in rainy conditions.

So, should you go out and buy a high-powered radar reflector? Not necessarily, but it's certainly prudent to check out your own vessel's inherent RCS. The ideal is to go out with a friend who also has radar and target each other at different ranges and headings. Remember that performance may be considerably diminished in rough seas. Ultimately, it's up to you how big you want to look, but bear in mind that the IMO is concerned enough that it may soon triple its already challenging RCS minimums. Very few yachts are SOLAS vessels, but we all share the same oceans.

It's also worth considering that for some boaters out there you might be the scary vessel  that doesn't see them. Study the RCS of any "small" boats you come upon when the visibility is good; excercise may teach you how to get the optimum target images from your set, and what might be missing when the fog does roll in.

On a final note, I'd like to issue a disclaimer. It seems I've written a string of columns concerning gloomy safety issues, but I certainly do not want to scare anyone away from boating. Being offshore, even at night, even in fog, can be beautiful and memorable and safe. Statistically, messing around in canoes or PWCs is more dangerous. But what the statistics don't record are yachtsmen's anxiety levels; inexperience, weather, and poor equipment can all conspire to suck the pleasure out of pleasure boating. If my cautionary columns help anyone increase their knowledge and confidence at the helm, that's a good thing.

Phone: (44) 01963 34184. Fax: (44) 01963 32604. www.sea-me.co.uk.

North Sea Navigator (Cyclops U.S. distributor)
Phone: (631) 757-7169. www.northseanavigatorinc.com.

This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.

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