Radar Use - The Sequel

[Ken Prichard]

I recently asked two specific questions regarding the use of marine radar. After some reseach involving various internet sites, the Canadian Coastguard and a lawyer I thought you may be interested in my findings. The lawyer does not specialize in Maritime law but did do some research and made some inquiries:1) If your vessel is equiped with radar there is no legal requirement to have it turned on unless visibility is restricted. The col. regs. state " Proper use of radar must be made if it is installed and operational". "Proper use" is accepted to mean; " A radar equiped vessel is expected to have the set in operation whenever manoevring in conditions of limited visibility".2) You will not "paint" a larger, or different, target on the screen of a receiving radar by having your radar operational. There are some sets that have built in signal detectors ( like a car radar detector ) but the on screen signal will be no different. Outside of the military, vessels so equiped are rare. The intent of their use is to alert the mariner to the pesence of a nearby marine radar. And no, a car radar detector won't work. They are set to a different frequency. A radar antenna in your rigging will, however, act as a radar reflector and will increase your cross section to another vessel. This happens whether or not your radar is turned on.I'm not presenting these findings as "law". Just what I came up with.

 

[Rick9619]

How about a radar reflector?

Ken,Being one who's cruising grounds (california coast) frequently have reduced visibility, I am curious. Are there any requirements to have a radar reflector on your vessel? Not withstanding that its a smart thing to have.I got pretty much the same interpretation about when to have your radar on. However, if you are radar equipped and smack another boat on the open water and your radar is off, even if it is a clear day, it may be causal when it comes to insurance payments.Typically, sailboats have a very small RCS (radar cross section) when approaching another vessel head on. Rounded masts, stainless, and radar housings all scatter radar pulses. The water also reflects the beam away from the sending radar. Your best reflector would be a big flat plate on the bow, but that is only good if it is pointed at the sending radar. So the spherical, and cylider type reflectors all work. Most importantly its not how your mount them (their reflectivity changes as your mast moves), its how HIGH or far from the water. The boats that have the capability to see your radar signal (from your turned on radar), ampify it and shoot it right back to ya. Hence they will appear as a more visible target at greater ranges on the typical 24k radars. Tis all smoke and mirrors.Cheers

 

[Ken Prichard]

Reflectors

I've read a fair amount about radar reflectors lately and it seems the metal thing most of us hang in our rigging is next to useless. Some British magazines rate a French reflector (tri-lens) as the best available.http://www.sailgb.com:80/p/trilens_radar_reflectors/

 

[Ken Prichard]

Tri-lens site

I'm not sure that linked worked so I'll try again.http://www.sailgb.com/p/trilens_radar_reflectors/

 

[Ross]

An electrical engineer on the wooden

boat forum has done considerable research into this matter and has found that a gallon size container filled loosely with 1/4 inch wide strips of foil 1.5, 2, 2.5, and 3 inch long will reflect better than any of the reflectors on the market. So perhaps a steaming ball so filled would be a good option. He uses gallon milk jugs.

 

[Rich (P303)]

CD's

Glue a bunch of old CD's to your cheap round ball shaped one you are using now. The "painted" image will look like a battleship out there.

 

[Clyde]

Using RADAR while underway

RADAR is considered a collision avoidance device used in conjunction with proper lookouts to avoid a possible collision. As soon as you are underway you are required to maintain a constant watch for traffic. You should have your RADAR on while underway, even in daylight, to provide the optimum collision avoidance coverage. Most recreational sailors turn on their radar only in bad weather or at night. If there is a collision and you didn't have your radar operational, even during daylight hours, you will be held partially at fault for not having a proper lookout and not having your radar on.From the U.S. Coast Guard FAQ:"Radar is not required on vessels under 1600 GT (Title 33 CFR part 164.35), however, Rule 7 states that proper use shall be made of radar equipment if fitted and operational. In other words, whoever has one must use it. The Navigation Rules are not meant to discourage the use of any device, rather they expect prudent mariners to avail themselves of all available means appropriate...as to make full appraisal of the situation (Rule 5), e.g. the use of radar. At issue is whether the use of radar is appropriate in the prevailing circumstances and that is a determination made by the Master; and, ultimately decided by a trier of fact. Should you be in a collision how would a judge/jury rule on your contention that the use of radar was impracticable (due to electrical drain, crew shortages, etc.)? Also, if a collision does occur, then there was obviously a risk of collision beforehand. Could the determination of that risk have been made sooner with the use of radar? It is difficult to answer such questions because the circumstances of each case are different. More importantly, remember that Rule 7 specifies that assumptions shall not be made on the basis of scanty information, especially scanty radar information."The courts usually blame both parties in a collision, based on the degree of liability. Admiralty law judges vessels with radar as having greater responsibility than vessels without radar in a collision. If you are sailing near shore, the excuse of draining down your batteries for not turning on your RADAR usually doesn't apply. If you had enough crewmembers stationed to cover 360° while underway, then you might only be assessed a smaller amount of blame in a collision if your RADAR wasn't turned on. The United States Coast Guard Auxiliary advises strongly the use of RADAR whenever a vessel is underway even in daylight. They had an article about this. Ultimately, whether you use your RADAR while underway is the captain's decision. Your civil liability of not having your RADAR in operation if you are in a collision will be determined by Admiralty court. Fair Winds,ClydeUnited States Coast Guard Auxiliary article on using RADARhttp://www.auxguidanceskills.info/press/radar.html

 

[Tom S]

Actually one of the least expensive reflectors

is one of the better things you can have on your boat - The Davis Echomaster. More cost does not always mean better reflection.One of the tests done on this is the 1995 US Sail testshttp://www.ussailing.org/safety/Studies/radar_reflector_test.htmIn the report it says "The table data are sorted first by X-band "visibility", the percentage of return greater than the threshold, then by average RCS for the reflectors with no return above the threshold.Using this criteria, the Davis Echomaster was the clear winner, but showed the deep nulls associated with an octahedral reflector"But offshore they sometimes use "s" bandConclusionsThe first conclusion is that there is no substitute for size when it comes to radar reflectors. The devices that offer smaller size and lower windage simply don’t work as well. With regard to the Firdell Blipper, it is a well packaged and clever device, but the models tested were not large enough to have much real value aboard a vessel. Larger versions would accomplish what GEC Marconi claims, but are not practical on small vessels.The Davis Echomaster (in the "Double Catch Rain" position) and the Lensref performed the best of all of the devices tested. The Lensref has no nulls, which is a tremendous advantage in terms of being seen, but the overall reflectance is marginal. If a Lensref is fitted on a sailing vessel, it should be gimbaled or made adjustable. The Davis Echomaster had stronger peak reflectance, but also large holes, which means that a large target would not consistently be presented on a ship’s radar.None of the reflectors would be more than marginally useful in offshore situations where only S-band were being used, except perhaps in calm sea conditions.The marginal performance of radar reflectors in general does not mean that they should not be carried. On the contrary, anything that improves a vessels radar visibility is worthwhile, particularly short-handed vessels and those without radar themselves.The Tri lens mention previously is probably the best -- but it too, is not perfectFrom Westmarine http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/RadarReflectors.htmTheTri-Lens RTE uses three Luneberg lenses providing strong returns. The combination of three very narrow nulls when the boat is level, and only slightly wider nulls when the boat is heeled up to 30 degrees, makes it one of the best RTEs on the market. We strongly recommend the two larger sizes; the smallest model suffers from the fourth power law as previously described.For less money, the Davis Echomasters are rugged and have very strong peak reflections when oriented with one of their "pockets" towards the radar energy. Their round plates are surprisingly more effective than similar reflectors made with square plate

 

[Manny]

More on the cd idea...

Couldn't you hang a bunch of cds from a line off one of the spreaders? Almost like a mobile?Ross, by chance do you have a link to the bottle with the foil reflector. I'd like to see what it looks like.Talk about really cheesy, how about a mirror ball??? ;D Manny

 

[Brian D]

Manny...

Here is the link to that Wooden Boat Radar Discussion. Very interesting.I think one of the key factors in the cut aluminum strips is the wave length of the strips. They are 1/4" wide and four length of 1.5", 2", 2.5", and 3". Each one of these lengths represents an excitable frequency. When struck by the radio wave, it will reflect it back without too much absorption because it is "tuned".For S-band radar (2-4 GHz), a halfwave would be about 2.8" on the high end.An example of what will not allow radio waves to pass is the Faraday Shield. Every microwave oven has a Faraday Shield in the window. This screen is tuned to block the waves striking it, therefore, you don't get radiated. I am building a reflector right now. It takes time to cut the aluminum, twist it like a noodle, and put it in the container. The container I am using is from CostCo, it held a bunch of nuts. Nice size. 5.5" diameter at the base, 6" tall, 4.5" diameter at the mouth.Science is wonderful.

 

[Ross]

Manny, The man didn't attach a picture but

said that he just used a gallon jug. How about a plastic halloween pumpkin? All you need is a container full of foil strips as I discribed.

 

[sailortonyb Allied Mis]

The standard criss-cross

The Echomaster, or any other of the standard round or square criss-crossed type radar reflectors sold by WM and just about everyone else work great. I am not stating this from theoretical numbers or calculations nor from engineers deigns. I know these el-cheapo's work great from experience. I was a professional boat cap't in the gulf on crew boats and small supply vessels. Also, on the larger platforms in the gulf we always have radar on for security purposes. Consider the stealth bombers. Its not just the radar reflective paint, its also no sharp angles to reflect radar signals back. IMHO, the best radar reflectors are the ones that have 90 degree angles in them.This gets us back to the old fashioned el-cheapo, hang from the rigging type normal looking radar reflector.Tony B

 

[Fred Ficarra]

Yep, If you want to look big

and that's the purpose of reflectors (IMHO) look for one that has an inverted pyramid shape. The el-cheapo's hung in the 'catch-rain' position have such a shape. No matter the orientation of the reflector, it will send the signal back. A quick reference too is to look at the structure of your automotive tail light lens. They also reflect.

 

[Don12364]

Some Information

1) You will not increase your chances of being seen by ships when running your own radar – but sure as hell increase your chances of seeing others.2) Please do not rely on any of these 'ham' solutions to making your own radar reflector. A great deal of research has gone into reflectors and if it were so easy then such gimmicks as described above would be commercially available.Remember small vessels may not be seen on ship's radars under some circumstances and the QinetiQ report below shows a zero chance of detection at 2 miles and 4 miles. How about that!!!For those with a maudlin interest please read the Marine Accident Investigation Board's reports as below. Two yachts run down by ships, the latter with three fatalities.The MAIB Reports are on:-http://www.maib.gov.uk/publications/investigation_reports/2003/p_o_nedlloyd_vespucci_and_wahkuna.cfmand:-http://www.rya.org.uk/NR/rdonlyres/60475AB0-CB12-45B9-BDCC-1E80129524D3/0/MAIBReport.pdfThe second report also refers to definitive tests on reflectors by QinetiQ:-http://www.maib.gov.uk/cms_resources/Radar%20reflectors%20report.pdfAlso a definitive test by Dick Honey and others on reflectors on:-http://www.ussailing.org/safety/Studies/radar_reflector_test.htmThe above reports clearly show that the only ‘safe’ way of sailing is to avoid ships at all costs. Radar reflectors as we know them only have a third or a quarter of the reflecting crossectional area needed by modern ship's radars with ARPA. A revised IMO spec has been in draft since 2003 and will recommend either an RCS of 7.5 sq metres or 10 sq metres and current yacht sized reflectors only give consistent responses of 2.5 sq m average and even this decreases when heeled. They also have nulls which render a small vessel invisible.The best solution is to carry an RTE (Radar Target Enhancer) and hope the ship is looking at its X band radar.I carry AIS linked to a laptop so I see everything over 300 Gross Registered Tons at 10 miles and the nav program warns me if anything will come within 1 mile. I feel sooo much more comfortable when crossing shipping lanes.Sorry about my rant but these days ships seem to pay more attention to their radars than to looking out of the bridge windows and we all need to know this.