|Topic Review (Newest First)|
|02-25-2007 05:09 AM|
Perhaps I should have explained better how radar range alarms work in practise. With the sea return and rain return dialed back to minimum settings the collision avoidance system will acquire and track waves and rain squalls. If the close range alarm does not drive you batty the lost target (target?) alarm will. Adjusting the radar gain, as well as sea and rain suppression, so as to eliminate the false returns results in a radar setting that will only pick up the Globetic London, 500,000 gross tons, and so, while they seem like a good idea from an engineering standpoint they do not perform in real world conditions.
Proper radar operation involves continual fussing with sea/rain clutter setting, depending on conditions. By doing so it is possible to determine if one is looking at a sailboat mast, or submarine periscope, or merely a dense spot of a passing squall. In my experience, on over twenty sea-going vessels, both the sailboat and periscope show up, on average, at six miles and often substantially less (if at all). I have picked up sailboats at ten miles and those must have had a reflector from what I was able to tell. Bearing in mind that the average sea-going merchant ship is travelling at 17 knots, he will have approximately 20 minutes to "see" you. If you happen to run into the Sealand MacLean at sea speed, the mate on watch will have approximately 2 minutes to "see" you. Obviously, anything that increases the distance that he can "see" you on radar is of benefit.
It is quite likely, if you are keeping a decent watch, that you will see the merchant ship long before he sees you. After all, you are on a white boat, with white sails, there are whitecaps on the water, and whiteish/gray rain squalls about-and you're awfully small. If you feel that a merchant ship has not seen you, and I'm referring to offshore primarily, it is entirely appropriate to make a VHF call, if only for a radio check. Believe me when I say that a voice coming over the VHF, that sounds like it's transmitting from right alongside you the signal is so loud and clear, will get the attention of the mate on watch who previously thought he was alone in his little section of ocean! If you're well offshore, he'll probably appreciate the conversation too. As always, female voices elicit quicker and more inquisitive responses!
Naval vessels are to be feared at all times for the following reasons: They often do not monitor the VHF radio as well as they should, being pre-occupied with six other radios squawking, and the sense that it is "merely" a civilian radio and of little consequence to them. Their radar is no better at picking up your sailboat than the merchant ship's. (Don't Tom Clancy me on that one. I've sailed with Navy ships in just such situations and while they may be tracking something 50 miles away, they can't "see" you any sooner or better than that rusty Greek tramp can.) And Naval vessels, due to the nature of their work have two nasty habits; they tend to change course for no obvious reason, often with a large increase in speed, and they think nothing of being in close quarters situations due to formation steaming and re-fueling at sea operations. Aircraft carriers are particularly to be feared. Remember that the captain of an aircraft carrier is a naval aviator and you can guess where most of his experience and training has been concentrated.
It would be a boon to all if a reasonably priced and sized radar transponder were available. Much like those found on the sea-buoys of major ports, they give an excellent radar return at an appreciable distance.
|02-22-2007 06:02 PM|
"Sailboats without reflectors make lousy radar targets"
There wouldn't be any sport in running them down if they were GOOD radar targets, now would there?
|02-22-2007 12:36 AM|
The fog will find you eventually in the Gulf Islands and St of Georgia. It's found me often enough.
To _not_ have a reflector is foolhardy -- it's got a high "safety per dollar" value.
Sailboats without reflectors make lousy radar targets -- I've seen them often enough on my own radar.
Spend the money, let people see you easily.
|02-21-2007 05:40 PM|
These things are meant to be permanently mounted. The 405mm model weighs 5.5kg and is going on the mast, just above my radar.
|02-21-2007 04:16 PM|
Are you going to permanently mount it or only hoist it on a flag pennant when needed?
|02-21-2007 12:13 AM|
You are the captain and are responsible for the safety of the vessel and everyone on board. If it were me, I would want to be as visible to larger vessels as I could possibly be, fog or no fog. Put up the radar reflector.
A collision at sea can ruin your whole day.
|02-20-2007 11:44 PM|
Luneberg Tri-Lens Reflector
In reading through this thread, I see that it has now been running for more than seven months. Over that time it has received opinions ranging from radar reflectors being useless to their being essential equipment. I see them as essential equipment, and so does Transport Canada:
"Vessels less than 20 m (65’7”) in length or that are constructed primarily of non-metallic materials must have radar reflectors, unless they are not essential to the safety of the vessel, or the small size of the vessel or its operation away from radar navigation makes compliance impractical. If properly positioned, they help larger, less manoeuvrable vessels detect your presence on their radar screens. They should be located above all superstructures and at least 4 m (13”1’) above the water (if possible)."
But selecting just any reflector is not as safe as you might think. Radar systems typically require a minimum of three consecutive "hits" or blips on a ship's radar before it can be acquired as a target. This puts a premium not only on the strength of the return, but also on consistent coverage to maintain a high Radar Cross Section (RCS).
The commonly used three intersecting disk style of reflector has many blind arcs and a rather low return rate. Their manufactures usually refer to RCS in terms of Peak RCS. What they don't tell you is this Peak RCS is rarely obtainable and that it doesn't happen when your boat is pitching or heeling. Neither do they mention angular coverage, which is most important when evaluating a radar reflector. This type of radar reflector's angular coverage is just 35 degrees wide.
In any sea state that offers a radar some sea return, your sailboat's intermittent and weak return signal is either lost in the sea clutter, or ignored as a false echo.
On my last boat I installed a 305mm Rozendal Tri-Lens Luneberg reflector with 330 degrees of coverage that was little impaired by heel or pitch. Everyone that I asked said that my boat painted like a large ship on their X-band radars. For my new boat I have specified the 405mm model, since its larger size shows-up on both X-band and S-band radars much better. I want to be easily seen.
|02-20-2007 12:56 PM|
larger pleasure craft skippered by an elderly gentleman who had too much wine
...your post is very true. One of the biggest problems and dangers there is today is from what I would call "waypoint" cruising...where a series of waypoints is entered in well trafficked spots from widely purchased cruising guides. Thus everyone transiting from Waypoint A to Waypoint B has entered the same coordinates and is travelling on autopilot on the exact same course governed by a GPS that is accurate to within 30 feet or so. Interesting things can thus happen when a sailboat is being overtaken by a powerboat or is on the same reciprocal course and not keeping an ever vigilant watch.
What I do with my waypoints (aside from NEVER using them to steer my autopilot) is to enter them .1 or .2 degrees off to seaward so that i am never on a common course with those that merely enter them from the chart books. (Yes I do check for a clear seaway to the new waypoint!
At the very least, it prevents me from being "waked" by those big power boats.
|02-20-2007 01:37 AM|
|Sailormann||Hmmm - nuisance ??? I can't tell you how reassuring that is But you are probably right. Anyway, if I were sailing an Ericson 30 (or any boat) in that area, the things I'd be most worried about are the other, larger pleasure craft skippered by an elderly gentleman who had too much wine with dinner. A lot of them have radar, and I'm hoping they don't have their range alrams turned off...|
|02-20-2007 12:59 AM|
While I agree with the thrust of your post I would mention that nobody uses range alarms on merchant ships. They are just a nuisance designed by engineers who've never stood a bridge watch. Regardless, a proper watch-keeper will have no need for such an item as he is watching visually and with radar in such a fashion as to make such devices unnecessary. If one were to wish to use one on one's sail-boat while anchored I would think that would be an appropriate use. The use of radar reflectors is possibly the best thing that the sailor can do to prevent themselves from becoming a rather low mounted figurehead on a much larger vessel.
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