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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #21  
Old 09-09-2006
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Radar Transponder (aprox$850) , [s-band only]

http://www.sea-me.co.uk/



The disadvantage of the passive reflector lies in the many directions in which its radar cross section is low, resulting in a minimal return.

The polar plot shows that Sea-me has a much more even response pattern and suffers from none of the gaps so typical of a passive device.

1. Greater detection range.
The strength of a radar signal falls off rapidly with distance. In the case of a passive reflector this degradation takes place over a distance equal to double the range (radar to target and back) whereas in the case of an active device, which is itself a transmitter, it only falls off over the return distance - and from a much higher amplified signal level. This means that Sea-me, an active device, has a greater detection range than the typical passive reflector.

2. A more consistent return.
Ships today use a system known as ARPA (Automatic Radar Plotting Aid). This enables the radar to emit an alarm when it acquires a target within its guard zones and thus to alert the watchkeeper. Target acquisition will only take place if the radar receives returns on at least 50% of scans. Two factors contribute to a consistent return - the strength of the returned signal and, because small boats yaw and heel, particularly in rough seas, the evenness of the return.

3. Better performance in clutter.
Performance in clutter (rain and wave) is all about signal strength. The single fact that Sea-me emits a stronger signal means that it performs better in clutter.

4. Better performance at heel.
The effectiveness of a passive reflector falls off rapidly as the boat heels, as you would expect of a device which is effectively a mirror reflecting in a single direction. The Sea-me device shapes the beam to provide an effective return even when the boat is heeled.

5. Ship detection alert.
Passive reflectors cannot give you any warning that you have been struck by a radar signal indicating that there is a ship in your area.
Sea-me, being active, knows when it has received a signal and can alert you with a flashing light, and if required, audibly. Sea-me thus enables you to sharpen up your lookout when necessary.
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  #22  
Old 09-09-2006
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Get one, get a radar while your at it
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  #23  
Old 09-09-2006
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i agree with smart captain on his post
you have to be prepared for any possible occurance at sea, this is what will make you a better sailor and keep you safe

nobody ever plans to be out on the sea in a squall but sometimes it happens you pick up a headwind and are forced to tack for a couple of hours to get to the next overnight point I also am a budgeted sailor and have the same thoughts but to err on the side of caution i always ask if it MAY make me safer on the water if the answer is yes then it becomes a required euipment within reason I.E. I can not afford a radar system so it is not considered a option
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  #24  
Old 10-02-2006
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sailaway21 is just really nice sailaway21 is just really nice sailaway21 is just really nice sailaway21 is just really nice
Radar reflector

Oh boy. I've been waiting for this one to come up. I'm the "other" guy out there. I'm driving upwards of fifty thousand tons of steel at seventeen knots. I have both my 3 cm and my 10 cm radars on. I have a able-bodied seaman as a lookout as well. It's blowing force 3-4, enough for some decent whitecaps, and it's kind of hazy. Pretty much any day at sea. My 10cm radar is for navigation and will not pick up a sailboat. My 3cm radar has a much sharper picture and will pick you, and submarine periscopes, up at approximately 6-7 miles. But there is a sea running and some rain showers and that obscures my 3cm. So because of the sea, I can't see anything on it within 3 miles. The rain squalls also white out sections of my screen. Think of the weather radar you see on TV-that's what my picture looks like. Even when I do pick you up you look like a tiny pinprick, I'm not even sure you're there at first. Now it takes me a good half mile or mile to make any effective course alterationm, and forget about stopping anytime soon. As, the previous response indicated, are you feeling lucky today? I have been refueling aircraft carriers in the Med., in formation with the rest of the battle group, with a third mate with his head in the radar, when he noticed a small return, six miles off, steady bearing. Visual id fo a sailboat. Called over to the carrier, "What do you want to do about this sailboat fine on the port bow?" Response, "What sailboat?" And that's the US Navy, with all the technology your money can buy, plus a bunch of signalmen lookouts. I've got 21 men on the whole ship period. What color is your sail or your mast or your hull? Probably not international orange are they. Why do you see the ferries paint their bridge dodgers int org? To be seen. You're just another whitecap out there. And I'm a good lookout. Is everybody? I keep my radar on even in good weather-I might see something sooner than visually. I've had you guys slide down the side half a mile off, out of no where, and that's close quarters to me! And my heart was none the better for it. You shouldn't be allowed to leave the dock without a radar reflector. I've hit whales and didn't know it 'til somebody walked up to the bow in the morning! Do you even think I'm going to feel you? You won't even scratch my paint. Don't ever forget the rules of the road. The first one is, the big boat makes the rules. Get a radar reflector, get the best one, and live to tell your grandkids how you saw the QE 2 ay thirty knots, with the bone between her teeth. Because the mate on watch over there doesn't have a story, he never saw you. Safe sailing my friend.
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  #25  
Old 10-02-2006
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Sailandoar- Given that many small boat sailors don't want to spend the money on a radar reflector and the associated costs to install it, what is the likelihood that they'll spring for an active radar reflector, like the SeaMe??? Close to ZERO. If they are willing to spend money... they usually want to spend the least possible...and anything that requires power on a continual basis is something they generally want to avoid.

Also, a radar reflector, like the Davis Echomaster, doesn't require power. When is the power on a small sailboat most likely to have problems... in rough weather... when are you most likely going to need a radar reflector/responder/radome? In rough weather. Which would you rather have, something that becomes a paperweight if your electrical system packs it in, or something that will just work, with or without electricity.

I know what my answer is... That's why I have a Davis Echomaster Deluxe on a halyard, and another one sitting as a spare in the companionway locker. Total investment for the two radar reflectors and halyard setup was less than $150 and about 15 minutes of time.
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  #26  
Old 10-02-2006
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Sailaway-
"I've hit whales and didn't know it 'til somebody walked up to the bow in the morning!" What kind a cook do you have on that ship, who's letting tons of fresh roadkill slip away like that?!
First you waste money on lookouts, then you waste more money or running the radars (plural!), then you hire a cook who lets roadkill slide under the keel.

No wonder my taxes are so high.
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  #27  
Old 10-27-2006
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Cool save your money

Save your money and do like the great sailor from Argentina Ernesto Saikin of the 30' S/V New Life, just returning home from a voyage around the world. A water jug full of aluminum foil hanging from the shrouds. On the radar it appears like a huge carrier. Amazing...
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  #28  
Old 10-27-2006
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Urban myth, Roger. It isn't that easy to get a good return from foil. The angles, and the dimensions, have to be "just right" and then, it's called "chaff".

I'd say buy some surplus chaff to have real fun, but IIRC the military stuff is matched for a different frequency.
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  #29  
Old 10-28-2006
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The other view

Hello,

I am going to take an opposite point. I don't think you need a radar reflector, and here's why:

-If you sail during the day and watch out for big boats (and stay out of their way) how will a reflector help?

-As already written by a number of people, most of the big boats won't (or can't) move even if they do see you.

I sail on the Long Island Sound, near Port Jefferson. There are frequent ferries between Port Jeff and Bridgeport, CT. I see some big barges, and other large traffic. The sound is wide (100 miles) but not that far accross (less than 15 miles where I am). The ferries travel at about 15 kts and they won't change course for anyone. It's easy to see a ferry, and also real easy to stay out of the way.

Regardless of wether the ferry sees me or now, *I* have to stay out of the way.

Barry
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  #30  
Old 10-28-2006
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Quote:
Originally Posted by BarryL
Hello,

I am going to take an opposite point. I don't think you need a radar reflector, and here's why:

-If you sail during the day and watch out for big boats (and stay out of their way) how will a reflector help?

-As already written by a number of people, most of the big boats won't (or can't) move even if they do see you.

I sail on the Long Island Sound, near Port Jefferson. There are frequent ferries between Port Jeff and Bridgeport, CT. I see some big barges, and other large traffic. The sound is wide (100 miles) but not that far accross (less than 15 miles where I am). The ferries travel at about 15 kts and they won't change course for anyone. It's easy to see a ferry, and also real easy to stay out of the way.

Regardless of wether the ferry sees me or now, *I* have to stay out of the way.

Barry
I would say your approach is a bit foolish. At night, in the rain or fog, RADAR is often the first indicator of your boat to a large ship. If a large ship has sufficient advance warning, they will often make a course correction to avoid a small sailboat, provided the sailboat is either stationary or moving in a predictable manner.

In the fog or rain, keeping a watch for ships is often not realistic, as the visibility is too limited to have sufficient warning of their approach in time to make a difference. A large freighter, moving at 15 knots can go from the visible horizon to you in a matter of four or five minutes, especially if you are on reciprocal bearings heading for each other.

Your approach may work on a sunny day, where visibility isn't a problem...but most of us sail in conditions other than just sunny days.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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