Active Radar Reflector - My recent experience

lw395 said:
The Echomax website says the position accuracy of the enhanced return is better than a metre.
So I think they must rely on isolation between receive and transmit antennas.
That seems consistent with the antenna pattern they imply from the heeled performance data.
Note that by 20 degrees of heel the performance is a very long way down on vertical.
I suspect that there is a null not far from 25 degrees of heel?
That would only be an issue if the radar was abeam of you.
Click to expand...

Thanks; I haven't been able to find equivalent data for the SeaMe, but that's reassuring about something I had been taking for granted.

I've done some work with radars (very different ones from marine radar!) and it seems to me that the problem is that the re-transmitted signal would saturate the receiver; given that both antennae (assuming they are separate) have to be omni-directional in the horizontal plane, there no way of physically isolating them. All the rather crude radars I've worked with had to blank the receiver for a period after the transmit pulse to avoid saturating the receiver electronics. Obviously there's some clever trickery that works, but I am curious about how they do it!
 
geoid96 said:
Which Channel are you talking about? If the Cherbourg-Portsmouth Ferry is steaming North and I'm going South the situation I described might well apply.
Click to expand...

Try here today

Fullscreencapture16112012121451.png
 
Slightly off thread I know but..............

.........to what extent is the range of the active reflector affected by its height?

I have seen them mounted on pushpits and on mastheads. My mast head is already a bit crowded with lights, aerials and wind stuff

Masthead would be about 14 metres above sea level, pushpit about 1.5 metres
 
Fascadale said:
Slightly off thread I know but..............

.........to what extent is the range of the active reflector affected by its height?

I have seen them mounted on pushpits and on mastheads. My mast head is already a bit crowded with lights, aerials and wind stuff

Masthead would be about 14 metres above sea level, pushpit about 1.5 metres
Click to expand...

Considerably. Radar is very much L.O.S so it's an easy calculation to work out the range difference pushpit to mast head.
 
AntarcticPilot said:
I've got a SeaMe, and think it is a valuable addition to the safety equipment on-board, far better than a passive reflector, and it is great to get confirmation that it really does work!

However, there is one technical issue that I'd be interested if anyone knows more!

......
Click to expand...

hmmmm .... grandmother and eggs spring to mind so I deleted my answer!

Buggered if I know how they stop the output from swamping the input and establishing a microwave equvalent of microphone feedback! :)
 
AntarcticPilot said:
Thanks; I haven't been able to find equivalent data for the SeaMe, but that's reassuring about something I had been taking for granted.

I've done some work with radars (very different ones from marine radar!) and it seems to me that the problem is that the re-transmitted signal would saturate the receiver; given that both antennae (assuming they are separate) have to be omni-directional in the horizontal plane, there no way of physically isolating them. All the rather crude radars I've worked with had to blank the receiver for a period after the transmit pulse to avoid saturating the receiver electronics. Obviously there's some clever trickery that works, but I am curious about how they do it!
Click to expand...

I think it may be as simple as the Active Reflector having its transmit and receive antennas effectively in each other's blind spot, by having them vertically in line.
It's not quite that simple as they will be close enough to be in 'near field', and there must be a danger of the transmit being reflected back to the receive by the mast or rigging.
I imagine you could get around that by gating the transmit so it would not re-trigger for a short period.
 
wotayottie said:
I can relate to your pleasure at finding an expensive toy working well, but just think for a moment. What is the benefit to you nor anyone else of being seen by radar at 20 miles? No one will take avoiding action that far off. Even at 5 miles its unlikely to trigger anything more than a mental note to keep an eye on that blip. I'm sure you can think of some unlikely scenario in which that range will be of value but IMO on day to day passages its no benefit at all. In fact I find no problem sailing without a reflector at all and the stats show very few boats ever being run down.

Just a thought.
Click to expand...

I agree in part... it really can depend upon the sailing you are likely to be doing.

In the past though I have been caught in a white-out during a day sail off Osborne Bay (Solent), and instead of one crew up front with a fog horn and me dreading the thought of a big ship coming through the gloom, I am now able to 'see' and 'be seen' by having an ais receiver, radar and an Active radar reflector.

Last winter I set the boat up for longer cruising.
This summer a 5 month trip going to Scotlands Western Isles and back from Portsmouth was accomplished.
We did use the radar, ais and Active radar reflector several times during the two thousand miles and most important for me, it gave swmbo far more confidence when she could concentrate her efforts on collision avoidance rather than "When we're hit, what shall we do first?"

The extremely sad result of the Ouzo recently may have been avoided if more money had been spent on 'toys'
Just a thought ;)
 
Last edited:
Fascadale said:
Slightly off thread I know but..............

.........to what extent is the range of the active reflector affected by its height?

I have seen them mounted on pushpits and on mastheads. My mast head is already a bit crowded with lights, aerials and wind stuff

Masthead would be about 14 metres above sea level, pushpit about 1.5 metres
Click to expand...

Line of sight is all you get I believe.

The technos may be able to advise..... If it's a very tall ship with radar or in my example a coastwatch lookout high on a cliff, does the ability for the radar to paint you and receive you as a target then merely come down to the power of the radar?
 
Last edited:
Scotty_Tradewind said:
Line of sight is all you get I believe.

The technos may be able to advise..... If it's a very tall ship with radar or in my example a coastwatch lookout high on a cliff, does the ability for the radar to paint you and receive you as a target then merely come down to the power of the radar?
Click to expand...

Range is limited by the power, and also by the length of time the receiver 'listens' for returns.
It is possible for a strong distant return to appear after the next transmit pulse and appear to be very close, but this is not normally a problem.
 
Scotty_Tradewind said:
Why not it's an amazingly short time if a ship is doing around 20knots?
Especially if you are below in the heads etc...

If I was on a run with poled out genny and a preventer on the main I would like to know when it's 15 miles away.

S.
Click to expand...

#44 would keep you focused 60/75 mls south of Dartmouth ( Tom Tit might have to wait :D)
 
Hoolie said:
I think you're all being bloody negative + thread drift.

I think the OP's experience is valuable and thanks for sharing it. An active radar transponder is a completely different animal to Class B AIS and offshore is definitely an asset, as confirmed by the OP. At least you'll be taken seriously by any large vessel picking you up.
Click to expand...

+1!
 
sailorman said:
#44 would keep you focused 60/75 mls south of Dartmouth ( Tom Tit might have to wait :D)
Click to expand...

WTF are you on about, Sailorman ? One minute you are on about ships 10 miles away, now 75miles away.

When crossing shipping lanes, its not the ships you can visibly see as the closest that are the problem, they pass in front of you, it is the ones just over the horizon which create the closest CPA.
 
Last edited:
moodyNick said:
WTF are you on about, Sailorman ? One minute you are on about ships 10 miles away, now 75miles away.

When crossing shipping lanes, its not the ships you can visibly see as the closest that are the problem, they pass in front of you, it is the ones just over the horizon which create the closest CPA.
Click to expand...

My dear chap may draw your attn to the AIS screen save on #44 :rolleyes:
 
Conachair said:
My steel boat gets picked up a long way away by the big boys. From watching them on AIS offshore I know they start any avoiding action way before they appear over the horizon, 5 miles away and it's already been done. A 20 mile return has benifits from being seen by the boats you want to be seen by.
Click to expand...

It's an interesting comment but I'm wondering how realistic it is. Dont for a minute doubt that you think you are correct but at 20 miles a one degree change of course would miss a target by 700 metres. So if a big ship thought it necessary to take avoiding action and miss you by 100m , he would need to change course by 0.15 degrees only. Even at 5 miles he would only need to change course by 0.6 degrees

Does AIS record courses to that accuracy?

Plus of course, at 20kn it takes an hour to cover 20nm. What yacht keeps a steady course for an hour. Or even 10 minutes?
 
wotayottie said:
if a big ship thought it necessary to take avoiding action and miss you by 100m , he would need to change course by 0.15 degrees only. Even at 5 miles he would only need to change course by 0.6 degrees

Does AIS record courses to that accuracy?
Click to expand...

Irrelevant, because a ship in unrestricted open water will not be aiming to miss by a hundred yards. Half a mile at a minimum, I would guess, and a mile or two is better.

pete
 
You must log in or register to reply here.

Other threads that may be of interest

F
Emtrak AIS transponder configured and working, not showing my position in Navionics unless
Replies
5
Views
291
FairweatherDave
F
zoidberg
Keep It Simple, Stoopid!
2
Replies
21
Views
894
thinwater
thinwater

Share this page

Top