Mailport May 15, 2002 Issue

Mailport: 05/15/02

Radar Riposte
The article "To See and Be Seen" (February 15), contains the following quotation from a Yachting Monthly article: "within a two-mile range, most vessels over 20 feet are likely to be just as visible without a reflector as with one." Although technically correct, this statement is incomplete and erroneously implies that passive radar reflectors are ineffective. I am concerned that PS readers will believe it and reject out of hand potentially life saving, inexpensive, and reliable passive radar reflectors.

The strength of the reflection depends on both the size of the target (the radar cross section or RCS), and its height above the water. The boat's RCS is concentrated in the hull very close to the water. The radar reflector is usually higher, in the rigging, and has a smaller RCS. Calculations verify the quotation in that, at short range, the reflection from the hull is stronger than the reflection from the reflector in the rigging and the reflector has little effect on the overall response. But it is almost irrelevant at ranges under two miles because there probably is not enough time to avoid a collision. The relevant concern is the maximum range at which the sailboat is detected. The statement ignores the fact that, at long range, the reflection from the reflector in the rigging is stronger than the reflection from the hull and the reflector increases maximum detection range significantly.

Although most passive radar reflectors for pleasure boats are undetectable in moderate wave or rain conditions, in relatively benign conditions when visibility is poor because of nighttime, fog, or drizzle, a good passive reflector is a cost-effective aid to collision avoidance.

-Philip G. Gallman, Ph.D
McLean, VA


I read your article "To See and Be Seen" with great interest. Our company, Rozendal Associates Inc., manufactures the Tri-Lens radar reflector whose performance was reported in your August 15, 2001 issue.

We do not claim that our radar reflector is a cure-all in preventing collisions at sea in all sea states. It is simply a piece of safety equipment recommended by every international maritime organization in the world, including the United States Coast Guard, that might save you and your boat's life some day. Its purpose is to increase the radar visibility of a boat. We believe our reflector, with its high radar cross section (RCS) and continuous coverage whose performance won't be affected by rolling and heeling, will increase the RCS of the boat. We strongly disagree with the quoted remarks from Yachting Monthly and Practical Sailor's inference that passive radar reflectors are useless, at least at close range.

The shortcoming of the tests referred to in the article was that no tests were conducted on radar visibility outside of 0.65 mile. We endorse the idea that the sooner a ship detects you the better. This would have to happen outside a 2-mile range in order for a ship to avoid collision. (Yachting Monthly, 1995 page 54.) This is what a radar reflector is intended to do—notify a large ship as soon as possible of your presence so that the crew will be on the lookout and be able to maneuver so as to avoid a collision. Many papers have shown that having a radar reflector mounted as high as possible on a sailboat enhances the probability of detection by a radar at ranges beyond 2 miles.

The mention of the RCS of a man being 2.5 sqm at water level can hardly be substantiated. Many papers have measured a man's RCS at between 0.5 and 1.4 sqm. This is not a very clean pattern and would result in the "porcupine" look.

All these tests, including those done in the UK, were at very close range. You would not be able to detect a man at water level at any great distance. With those considerations it makes perfect sense that you would want a reflective object as high as possible above water level to allow detection from ships far out at sea. This means a radar reflector.

The recommendation to use an active transponder came without mentioning the shortcomings of that system. First, they cost around $1,000, not something everybody can afford. Second, they are difficult to set up. Third, they only transmit X-band radar. They do not have S-band radar. Finally, the amplifier in the active system can be saturated by high peak pulsed power from radar systems, making it ineffective.

While the concluding portion of the article points out conditions that must be met in order for a ship to avoid a collision with a small boat, it is important to note that the small boat owner has no control over those conditions. What he can do is provide the protection of a radar reflectivity system. And it is he who must decide the price he can pay with a consideration of the pluses and minuses of all the systems out there.

-Tim Rozendal
Santee, CA


Dick Honey says "Multiple reflectors could help." In 1998, prior to my crossing the Atlantic on my Columbia 8.7, I fitted a small HYE 11" reflector close to the masthead on the starboard side of my mast (about 35' above the water) in addition to my Echomaster hanging from the port spreader  (about 20' high). Most ships I spoke to on VHF reported seeing my boat at better than 10 miles, and the captain of a Hapag Lloyd containership en route to Charleston told me: "You have a very good echo; not a ship's echo, mind you, but a very good echo." I attribute that to the fact that ships' radars cannot distinguish two reflectors less than 20' apart, just as our small 1.5 KW radars cannot distinguish targets less than 1/8 mile distant at 8 miles; in both cases targets are given as one bigger, single echo.

-John Somerhausen
Douglaston, NY


Leaky Pilots
I must disagree with Nick Nicholson's statement that autopilot failuresare often due to undersizing.  My experience is with tiller-mountedpilots, which differ in construction and configuration from wheel orbelowdeck pilots, which may contribute to my different experiences.

I have just purchased the fourth autopilot for my boat in 10 years.  Ihave used both major brands (currently Raytheon and Simrad)  with similarexperiences.  I have always bought the bottom-of-the-line model.  My boatdisplacement is at or slightly above the maximum recommended for thosemodels, but it is a trimaran with a very light helm, and I have fewcomplaints on how the pilots steer the boat when they are working.

In none of my units has the motor or drive system been the source of theproblem.  In every case it has been the case leaking water into the electronics and ruining the control circuitry.  Two of my units actually failed while in use when I got caught in a period of extended rain while cruising.  I don't consider this to be abusive service, since I  can only assume they were designed to be used in an open cockpit. Since the more expensive units have the same cases with additional features and more powerful motors, I don't see how they would provide longer service life; they are just more expensive to replace when they leak water and flake out. 

My latest unit is a Simrad, which they claim to test by submerging in salt water and driving the pushrod in and out for an extended period of time. I'll see if this ends up being a more reliable unit in real-world conditions.

-Norm Hansen
Highland Beach,  FL


Where Credit Is Due
To ASAP Supplies, Beccles, Suffolk, England: "I own a Moody 425 and would like to note the great parts service I get from a company called ASAP in the UK, not to mention the great service we get from Moody. My experience is that ASAP can get a sailor parts for UK and European boats with a turnaround of about seven days. I have a Ford Thorneycroft engine, for which they have always been able to fill the order. I have been able to get hard-to-find plumbing and strainer parts and electrical parts also from ASAP. They have a knowledgeable staff and respond quickly to e-mails. ASAP is definitely an asset if you have a foreign-built boat, especially one built in the UK. E-mail for ASAP's Mark Reynolds: Website at"

—Greg Navarre, S/V Siren Song

To Mystic Stainless and Aluminum, Mystic, CT: "I recently purchased and installed a mid-cockpit foldaway boarding ladder from Mystic. The ladder's quality and finish are excellent, and I received it in a timely manner. However, I found the installation on my boat to be difficult due to my full-cover sunshade. Much to my appreciation, Charles Marques at Mystic exchanged the attachment mounts several times, being very patient with me until I was satisfied with the resulting installation. All this without extra charges. The service I received far exceeded my expectations, especially since the errors in ordering were mine. I was thrilled to do business with Mystic Stainless."

—Bob St.Dizier, Slidell, LA

To Marinco, Napa, CA: "I have a Marinco inlet/outlet on my '85 Hunter 31. The rear protective cover and cable cinch had deteriorated. I contacted Marinco for a replacement. David Colclough of technical services there e-mailed me back immediately and said one would be sent without charge as a warranty issue—all this for a part that could be up to 17 years old. Hats off to Marinco."

—Tim Holt, Daphne, AL

Comments (0)

Be the first to comment on this post using the section below.

New to Practical Sailor?
Register for Free!

Already Registered?
Log In