Passive Radar Reflectors - Not a Troll!

[BruceDanforth]

I wonder how useful the test report is: they have all the anechoic foam and all the kit but a real world reflector is shaking around on a mast or possibly dangled from a string shaking round on a mast. They testers don't seem to have bothered much to simulate a realistic environment, just plonked the thing on a polystyrene cone.

 

[AntarcticPilot]

crossing Biscay last year, 40ft with passive reflector,called up container ship 4 miles off port bow.
Me : Vessel X,IN POSITION Y ,THIS IS YACHT Z, ARE YOU AWARE OF MY PRESENCE.
HIM: I THINK YOU MAKE MISTAKE,NO VESSEL IS WITHIN 7 MILES OF MY POSITION.
ME: PLEASE CHECK FROM YOUR STARBOARD BRIDGE WING
HIM: AHHH---- YES, I SEE YOU NOW,YOU ARE VER' SMALL!



Suspect radar was off( visibility WAS good) . To be fair he rsponded fairly quickly.

Well, the much quoted report from Qinetic basically says that passive radar reflectors are worthless except under conditions that sailing craft don't and can't fulfil. It doesn't say it in those words, but that's how I interpret it, reading somewhat between the lines, and with background knowledge of HOW difficult it is to set up a retroreflector so it works. Basically, even if a brand new reflector works, it probably won't maintain the required accuracy of the reflecting surfaces after a season's use. And the reflector will have to be large enough to impose other serious problems such as excessive windage aloft to be of any use. ANY roll, heel or pitch will put the reflector outside it's operating parameters, and will make the reflection appear to be intermittent, and so likely to be filtered by the circuitry of ship's radar, as other users have pointed out.

It is worth remembering that the hole in the water made by a GRP yacht is at least as big a reflector as the titchy thing up the mast!

I have a SeaMe, and am confident that I will show up on a ship's radar. As it indicates when it is transmitting a pulse, I can tell if it is working; and knowing that you are making a reflection like a super-tanker is a great comfort!

 

[fireball]

Having just done my first channel crossing with Radar (been across before - just not with Radar!) I was quite impressed by the sensitivity of the unit - it showed up big ships and yachts with little issue - I'm not fully conversant with the unit, but to me - if it shows a blob on the screen and it appears to relate to a yacht that I can see (and checking through binos it has a passive reflector) then I'm happy that it's working.
No system is perfect and I expect that in rougher conditions there will be more sea clutter, but then I wouldn't rely on the other parting having seen me.

 

[Evadne]

I was tempted by the Sea-Me, but apart from the disinterest shown by the rep. at the (London) boat show, the one thing that really put me off was my own experience: The first time I can remember really, really needing to be seen on radar was when we were drifting, no anchor or battery, a few miles off Folkestone. It was flat calm and the admiralty pattern folding reflector worked a treat, a Sea-Me would have been no use whatsoever. You do need a passive reflector anyway.

 

[AntarcticPilot]

I was tempted by the Sea-Me, but apart from the disinterest shown by the rep. at the (London) boat show, the one thing that really put me off was my own experience: The first time I can remember really, really needing to be seen on radar was when we were drifting, no anchor or battery, a few miles off Folkestone. It was flat calm and the admiralty pattern folding reflector worked a treat, a Sea-Me would have been no use whatsoever. You do need a passive reflector anyway.

I suspect you've found just about the only conditions under which a radar reflector is useful - flat calm, hence no sea-clutter, no heel, roll or pitch! But even so, I would argue that under those conditions, the hole in the sea made by your hull is making as big a return as the reflector. Without comparative information about a boat in the same position as you but without a radar reflector, we can't be sure.

As I can't start my engine without battery power, and certainly can't sail into my marina berth (a: because it would be difficult if not impossible and b: because the marina rules don't allow it), I am paranoid about making sure I have a good charge on both batteries. The SeaMe takes a miniscule drain on the battery, so I regard it as far more reliable than a reflector, which I regard as being of at best marginal value.

 

[Evadne]

The trouble is, I think, the oft quoted "hole in the water" is nothing more than another wave, especially when the wave height gets above a couple of feet. I have been on the bridge of a coaster, looking at the radar when a 40-footer gybed away from us. With the sail perpendicular to us he had a great reflection, but at 45 degrees or so he was invisible at a range of less than 2 miles. He was carrying no reflector at all.

It's probably a reflection on the state of my boat over the years, but I would never ever rely on battery power, which isn't the same as not making use of it, where an alternative is available.

 

[Genoa]

Maybe we just acept that BIG has right of way ... if you can see them keep clear!
As has been stated, even with a Sea-Me, you can do everything to make yourself visible, but you cant make a "junior" watchkeeper do anything (like turn the radar on!)
I keep a couple of flares to hand if I dont think I can see them with enough range. I also use the AIS to find out what they are up to, not to tell them about me - I don't believe they'd care
(b)

 

[jimi]

Actually, you're better off if you are invisible .. cos you can keep out the way and not worry about them altering course to avoid you! But sadly we must assume that we've possibly been seen (or possibly not) and that the ship may or may not alter to avoid, it puts a lot more variables into the equation!

 

[snooks]

I dont want to put you off installing a good radar reflector, but please dont be fooled into thinking people in the Solent are looking at their radar screens!

On Saturday I was looking at my radar ...I was testing out the self leveller to see how much it affects the picture when the yacht is heeled.

By "heeling" the radar around 20-25º I can make just under 1/2 the targets disappear as if by magic!

We've got some more testing to do, but first impressions show it does make a real difference to the radar picture

 

[AntarcticPilot]

The trouble is, I think, the oft quoted "hole in the water" is nothing more than another wave, especially when the wave height gets above a couple of feet. I have been on the bridge of a coaster, looking at the radar when a 40-footer gybed away from us. With the sail perpendicular to us he had a great reflection, but at 45 degrees or so he was invisible at a range of less than 2 miles. He was carrying no reflector at all.

It's probably a reflection on the state of my boat over the years, but I would never ever rely on battery power, which isn't the same as not making use of it, where an alternative is available.

I think you've made my point for me. The radar reflector is useful only under the same conditions as those where the "hole in the water" will stand out as a valid return; that is, conditions where there is little or no surface clutter, and where the boat's attitude is stable and upright. I read the Qinetiq report, and it is difficult to see that radar reflectors have any significant effect EXCEPT under conditions where the vessel is stable, and where a weak reflection can stand out from surface clutter. Others will give chapter and verse about radar cross-section, but ultimately a radar reflector makes a weak reflection a little less weak - and then only when the conditions are right, and you have a pretty large piece of kit mounted high up in the rigging. AFAIR, the Qinetiq report makes it clear that only larger reflectors are useful; remember that it is something that doesn't scale with the size of vessel - a small vessel needs just as big a reflector as a larger one.

I personally do not wish to rely on a radar reflector to make me stand out from the surface clutter at any range that would allow a ship to take meaningful action; recall that we may be talking about ranges of many miles for a ship at cruising speed. Others have pointed out that ship radars are often deliberately adjusted to eliminate weak and intermittent echoes - and that is what you will be with a radar reflector under normal conditions. I've seen the reflection from quite a substantial vessel - a small coaster - from the bridge of a ship, and it gave a weak reflection on the main bridge radar; you had to watch the display for several scans to see that the reflection was burning in at the same point each scan. And that was at a range of less than 5 miles. I was on the bridge of a Royal Research Vessel; these are well run vessels that (in this case) depend on radar to avoid icebergs!

A reasonable compromise might be to stow a substantial folding reflector for use when electrical power fails, but for normal use to have an active transponder.

Incidentally, in all the discussions of electrical equipment, the issue of failure of power always comes up, especially when we are talking of safety critical kit. There must be a market for someone to produce an emergency power supply, based on some cheap and reliable technology? After all, we're only talking about power requirements of a few watts to run safety equipment only.

PS, Just re-read the Qinetiq report. They state quite unequivocally that the Sea-Me is the ONLY system that fulfils existing and proposed ISO standards for radar reflectors, is the only (commercial) system that works at relatively high angles of heel while still providing a radar cross section exceeding 10 metres square. At 20 degrees heel, it was only surpassed by the £2,000 reference system! The system they state is the best passive system is the tri-lens system, which is VERY heavy (5 kilograms). They also state that most low-costs systems will simply lull users into a false sense of security!

 

[fireball]

Just to bring it back to the beginning ... the OP was intending to do most of their sailing in the solent ... where "ships" do not use radar to avoid collision with small boats because there is nowhere to avoid to! Ferries may well do, but TBH you've got to be out in some pretty horrendus weather not to be seen in the solent....