To the editor: In reading Steve D’Antonio’s recent article on radar (“Radar installation,” Issue No. 152, March/April 2006), I noted that he recommended against using a higher, mast-mounted radar antenna.
I don’t agree with the assertion that a 32-foot-high antenna will have difficulty detecting a jetty or buoy that is closer than 145 feet. We have safely piloted our boat Theodora with a 32-foot-high, mast-mounted radar antenna into the most fog-shrouded harbors from Digby, Nova Scotia, to New Haven, Conn., for 25 years. We have always been able, in calm conditions, to observe our approach to lobster pot buoys until they disappear in the sea clutter.
Although the radar beam is often approximated as wedge-shaped, there is power in the higher-angle radiation lobes and, since the power reflected from an object varies as a square of the distance, detection of nearby objects is greatly favored.
In addition, by having the radar antenna mounted so high, we have no concern about looking into a focused beam of radiation while standing on the cabintop or mast step while furling sails.
Finally, aesthetics: the pleasing look of a radome mounted on the mast above the spreaders should be compared with that of one perched on top of a pole protruding non-symmetrically from the transom.
– Peter Fowler lives in Ipswich, Mass.
Contributing editor Steve D’Antonio responds: Thank you for your note concerning radar installation. I wouldn’t begin to argue with the experience and results you’ve had with your own installation. My comment concerning minimum range was a generalization. When referencing the minimum range issue, I wrote: “these figures are approximate and may vary from manufacturer to manufacturer.” The statement wasn’t based simply on my experience with just one boat but on scores of radar installations I’ve carried out or supervised during the nearly two decades in which I’ve worked as a professional in the marine industry. Not all of those radar installations exhibited the characteristics of minimum range that I described, but many did.
David Burch has logged more than 70,000 miles at sea and is the director of the Starpath School of Navigation. He is the author of nine books on the subject of marine navigation including Radar for Mariners. He states, “In the radar manual’s technical specifications for minimum range, they are not referring to the minimum displayed range, but rather to a practical limit to the closest object that can be detected based on the characteristics of the radar antenna and associated electronics. This can be an important operational issue when navigating in very close quarters such as a marine or narrow channel in thick fog. When it comes to minimum range, antenna location is crucial, both with regard to elevation and obstructions. A beam emanating from a 40-foot-tall antenna first hits the water at about 60 yards from the base of the antenna. It will see things closer that are raised some height above the surface, but the main point is this geometric factor could easily increase the minimum range above the quoted specifications for some installations.”
If your radar is capable of detecting objects that are closer than its theoretical minimum limit, then you’re ahead of the game, but this is by no means an absolute for every installation. As far as aesthetics and symmetry are concerned, I’m afraid in my book they must take a back seat to functionality and safety (As I mentioned in the article, a radar antenna must never be installed where it will illuminate crew members.) Dedicated pole mounts work well and tend to, in my experience, be more reliable from an electrical standpoint (less chafe and sail buffeting, as well as improved service accessibility) and no customer of mine has ever complained that it didn’t afford him or her the radar’s advertised maximum range because it wasn’t mounted higher up on the main mast.