Decision, decisions, verse 2 - Radar Reflectors

We all know that having a radar reflector is a good idea. Anytime you sail anywhere near commercial shipping lanes, it is a good idea to be seen. For those of us that sail in the Salish Sea we have frequent encounters with commercial shipping of all kinds and have to cross these commercial lanes to get most anywhere. Fiberglass or wooden boats don't show up on radar so we usually use some type of device designed to reflect back the radar signal to it's source so that we can seen. All very good and reasonable.

For Legacy, I have been thinking about what type of reflector to use. It was suggested to me by Ron Marcuse on the Catalina 400 Yahoo group to consider a Tri-Lens reflector. As I looked into it, what I found out was a bit distressing.

For years on our boats, our family has used an octahedral reflector like the Davis Echomaster. We just assumed this would work just fine. Most of the time we hoisted it on a spreader halyard using the handy attachment points at the top and bottom of the reflector. This placed the reflector in the vertical position, rather than the ideal "catch rain" position (as shown in the photo). What I didn't know until I did a little research, is that hanging the reflector vertically reduces it's effectiveness significantly. According to testing done by a number of organizations, including Practical Sailor and the UK Marine Accident Investigation Branch, this design simply is not very effective at best, and is less so if not properly mounted or if the boat is on a heel. The problem is that if the reflector is oriented just right to the radar source, it reflects pretty well. However, is also has a lot of dead zones, angles where there is would be no return to the radar source. Apparently, many commercial radar systems have alarms who will only sound if it picks up a consistent radar target. If the target keeps disappearing, the alarm won't sound so you are at the mercy of whoever is manning the radar display. So, while the Davis Echomaster is relatively inexpensive (for a piece of boat equipment), it may not be worth the bother.

So if what I've used for years isn't very effective, what about the Tri-Lens? The Tri-Lens uses three Luneberg lenses to focus the radar energy and then reflect it back. Testing reveals that it is very effective without the large dead zones in the octahedral designs. This makes the average Radar Cross Section, much better. The problem though, is that for any radar reflector, the strength of the return signal is based on it's Radar Cross Section (RCS) . The RCS is related exponentially to the size of the of the reflector. Also to be effecting the cross section size of the reflector needs to be at least a few times the size of the wavelength of the radar signal, which for the S-band radar used by many (most?) commercial vessels, is about 4".

All this means is that the standard Tri-Lens, where each Luneberg lens is about 5.25" inches in diameter is marginal. The design produces a very consistent signal with few dead spots that is effected little by heel. However, that consistent RCS is not that large. The large Tri-Lens has Luneberg lenses that are about 7.25" in diameter and provide a much better signal return. However, the standard Tri-Lens already weighs about 5.5lbs. The large Tri-Lens is about 15 pounds!

Cost is another issue. The standard Tri-Lens is over $300 at West Marine. The large Tri-Lens is over $800. They also have a mini Tri-lens that is under $200 but from what I can tell, it wouldn't be worth it.

There is another option. The Echomax 230 reflector is a series of stacked corner arrays in a plastic cylinder. It performs very as long as it remains upright. As soon as the boat heels, even a little, the performance drop way down. This makes using it on a sailboat under sail problematic. It still has the same problems of expense and weight as the Tri-Lens. The Echomax 230 weighs about 5.5lbs and, with mast mounting bracket, costs over $350 at West Marine.

So what to do? The Davis Echomaster might get you noticed in the fog if the radar watch on a commercial vessel was paying attention and the vessel was in exactly the right position and the reflector was mounted exactly the correct way. Too many "ifs" for my liking. Still, it is inexpensive. I think all things considered, the standard Tri-Lens would be the best option, balancing performance, cost, and weight. I could mount it a foot or two above the radar dome on the mast and it would be reasonably high, and out of the way of most of the rigging.

We'll see....