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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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  #11  
Old 02-19-2014
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Re: Radar signature

Quote:
Originally Posted by FSMike View Post
I have a vague recollection of somebody (the Pardeys?) stuffing a hollow wooden mast with foil and having good reports on its signal return. If it wasn't them I apologize.
That's correct. It was the Pardeys. They put long strips of aluminium foil inside their hollow wooden mast (box construction) and had excellent results. I think this will only work on a wooden mast however.
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  #12  
Old 02-19-2014
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Re: Radar signature

We have over 100 large ship interactions, in open waters, per year and talk on the VHF to at least 25.

Even though we transmit on AIS we have to call them on the VHF to get them to look at their radar and AIS. At least 50% of the ships we call take up to 5 minutes to acknowledge our presence.

Except perhaps in fog, imagining that they are looking for small blips on their radar will get you killed.
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  #13  
Old 02-19-2014
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Re: Radar signature

I agree with York, while there is nothing wrong with installing something to try and reflect a better radar return I think it gives people a largely false sense of security. Actively monitoring your radar and AIS if you have it to avoid the big boys is by far the safest route to go. To answer the OP's question, we have the Davis and have viewed the sailboats radar return from another boat and it is quite visible.
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  #14  
Old 02-19-2014
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Re: Radar signature

My random thoughts...

The corner reflector (the spherical type with intersecting disks) is designed to work at all angles of heel since the idea of the "corner" is to create a 180 degree reflection using the two or three surfaces of the corner as long as the radar enters the corner +/-45 (90 degrees of returnable angle) degrees. In the spherical design once that corner rotates out of it's returnable path the next one rotates in so it works at all angles. The strongest return is when you have a whole disk aligned perpindicular with the source since you basically have two corners reflecting at that point, but on a bobbing rocking boat (The source is also rocking and bobbing) it's impossible to keep it aligned without some active alignment. The bigger the cross section reflector the bigger the return. Unfortunately the size of the disk that can be reasonably placed in a sailboat's rigging is somewhat small.

Putting metal in a metal mast won't accomplish anything. The radar is reflected by the mast itself, but the circular shape of the mast only returns a small portion to the source as the rest is scattered radially, and a boxed mast (square tubing) would only reflect, although very well, when it's aligned perpindicular to the source (vertically and rotationally). A wooden mast is basically transparent to radar so metal in a wooden mast would be of benefit.

Also, adding to it is the radar operator. If he has his gain turned down to eliminate sea clutter and only see the signature of a 500 foot steel hull so he doesn't have to stare at the screen except once in a while when there is a return, you won't be seen no matter what kind of dinky reflector you have.

AIS is cool but not everyone has them yet. And you can still run into another smaller pleasure boat not required to carry it.

So best I can offer is: Do what you can, keep a good watch when you can, keep some rum close at hand for the close shaves, and pray to the gods for safe passage.
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Last edited by CaptDave; 02-19-2014 at 09:55 AM.
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Re: Radar signature

Here is a test from 2005 - don't think much have happened since then
http://www.yachtingmonthly.com/fileB...ce_ym_june.pdf
One more
http://www.maib.gov.uk/cms_resources...s%20report.pdf

Last edited by knuterikt; 02-19-2014 at 10:12 AM.
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  #16  
Old 02-19-2014
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Re: Radar signature

got three little plastic lobules packed with reflectors mounted to the mast just above where the storm jib stay goes. Surface is smooth so doesn't interfere with lines/sails. Weight is minimal. Thing is white so not a eye sore. Blocking brand name. will post if it comes to me. Had friend check out if I show up on his radar. At 10m at least in absence of sea clutter/rain I do. Might be a good way to go. Running radar is a huge draw. When sailing usually leave in standby and pulse every once in awhile. Turn if off if not in lanes, fog etc. Now with commercial traffic required to have AIS think rather then blowing money on active returns spend the money on AIS.
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Re: Radar signature

Viking tri lens standard
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Old 02-19-2014
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Re: Radar signature & Radar Flare

The report referenced is what I used to select the TriLens. I have not heard that wet sails impact performance. Makes me wonder what happens with sails that have a carbon fiber matrix laminated inside.

I always wanted to have a few radar flares on board for emergency but I could never find a place to buy them. A radar flare launches a whole lot of aluminum chafe or streamers and makes a temporary radar image about the size of a supertanker.

GTJ
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Old 02-19-2014
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Re: Radar signature & Radar Flare

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Originally Posted by SailingJackson View Post
The report referenced is what I used to select the TriLens. I have not heard that wet sails impact performance. Makes me wonder what happens with sails that have a carbon fiber matrix laminated inside.

I always wanted to have a few radar flares on board for emergency but I could never find a place to buy them. A radar flare launches a whole lot of aluminum chafe or streamers and makes a temporary radar image about the size of a supertanker.

GTJ
That is a new one to me.
So you launch your radar flare.
You are only a mile away and suddenly look like an aircraft carrier.
The guy on the taker bridge has heart failure and runs you down.
Unintended consequences.
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Re: Radar signature & Radar Flare

Quote:
Originally Posted by SailingJackson View Post
The report referenced is what I used to select the TriLens. I have not heard that wet sails impact performance. Makes me wonder what happens with sails that have a carbon fiber matrix laminated inside.

I always wanted to have a few radar flares on board for emergency but I could never find a place to buy them. A radar flare launches a whole lot of aluminum chafe or streamers and makes a temporary radar image about the size of a supertanker.

GTJ
How long will it last?

What about a DIY project, it's only strips of tin foil and a launch system

The British Harriers used that stuffed behind the airbrake as a one dose chaff in the Falklands war.
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