Radar reflector for small vessel ?

[LittleSister]

There's no requirement to have a reflector, but it is undoubtedly safer to have one.

I disagree. There is severe doubt about the effectiveness of most of the passive radar reflectors of the sizes and types used on small to medium sized boats. Having one may or may not increase one's visibility to other vessels using radar, and may give the boat owner false confidence they are visible to other shipping.

I am not for a moment suggesting not having one, but cautioning against false expectations of how much, if any, additional radar visibility is actually being achieved.

The OP has a 25' motorboat.

The boat itself, and it's contents (especially e.g. engines), will reflect radar, but not necessarily strongly or at all consistently.

It is not actually impossible, but decidedly impractical to carry an effective-sized conventional passive radar-reflector on a boat this size or smaller. Size is extremely important in the amount of refection that can possibly be achieved, and the design (and correct orientation mounting) of the reflector is very important in determining how much of such potential reflection is actually achieved from different angles both from the heading of the boat and vertically from the horizontal as the boat is heeled or rolling.

In an attempt to overcome the size challenge, many sailing boats have a patent-array-in-a-drum type reflector mounted on the front of the mast, but these apparently suffer from being screened from a significant sector aftwards by the mast itself.

An active radar reflector apparently overcomes most of a passive radar's shortcomings, but at a cost not all can afford or tolerate, and is of course dependent on the continuous availability of a power supply (though rarely a problem on modern equipped boats). The model depicted in post #7 operates only on one of the two radar bands that ships might be using. Two band types are even more expensive. I've never been clear how much of a disadvantage the lack of the other band is. (Neither do I know how consistent (or not) the re-broadcast signal is around the 360 degrees horizon, or at different vertical angles fro the horizon.)

How visible you are, even with the best kit, will very much depend on the weather, how rough it is, the quality (or otherwise) of the radar gear in use by other vessels, and the settings the operators have applied to their gear.

Of course, in a big swell your boat and radar reflector of either type may well be screened from radar view a significant amount of the time, and hence not be picked up (see srm's post 20 above.).

One can only do what one can to increase the likelihood of radar visibility, depending on boat size/type, depth of pockets, etc. and hope for the best. Don't bank on always being seen, though!

 

[wonkywinch]

I don't have a radar reflector fitted but I do have AIS transmitted and a new (B&G) radar that picks up kayaker and larger pots (in calm seas).

Do I need to buy a cheap (ineffective) reflector to keep any French inspectors happy on a forthcoming trip? I believe inspections are up with the new immigration rules.

 

[Daydream believer]

I have a pair of the 100mm diam reflectors as shown in#12. The tests do not rate them very high. They are mounted on the mid shrouds so they are at an angle & one is more upright when the yacht is healed.
I was picked up by a lifeboat in big seas & F7 at night. The following day the skipper came to see me & commented that the radar return was so good. I replied that it was because the lifeboat probably had excellent radar. He pointed out that it was not the case & the vessel was due to go for a refit soon & radar was on the list of upgrades.
I later spoke to a radar expert who said that sometimes the sum of the 2 can be greater than each single reflector & that having 2 reflectors as I have is a good idea.
However, I later added an Echomax plus AIS transponder & was almost rundown by an Evergreen ship in the Black Deep - being missed by about 1.5 boat lengths.
I think the best reflector is the mark 1 eyeball

 

[Daydream believer]

I was reading somewhere that if I am at sea I need to have a radar reflector. I have a small sports cruiser Glastron GS 249 with no radar arch, so my question is what radar reflectors are mostly used for a 25ft craft?

Just out of interest
Would an average private radar operator( or even a commercial ship operator) pick up the Op's return in a cluttered area, if it was moving at, say, 14 kts.( or whatever speed it does) Even if that return was fairly good.

 

[Alicatt]

The majority of pleasure boats I see here are steel hulled in the 10 to 12 meter size, and with the small radar reflectors in a tube 40mm or so in diameter and about 30 to 50cm in length I wonder how effective they are compared with the large steel hull and aluminium superstructure of the boat it's self.
My little boat is plastic, it's even in the maker's name Placom which is Plastic Combination, my boat is not that high either having a 2m air draught and that is to the top of the cockpit canopy and having no mast to stick a reflector on to, the police were quite insistent that a reflector was needed and this is for the inland waterways not out on the open sea.
Been searching the local dealers for a reflector and the Plastimo ones with a mounting base are €29, I guess that is what I'll get.

 

[Refueler]

My SR25 with sails up ... no reflector ... F4 and heavy swell - hull was dipping near enough below swell head ... mid Baltic ...

Small Feeder Container ship who I had 'words with' for passing too close ..... my cabin was an absolute mess from his passing ..... he reckoned he had been tracking me on radar for about 10nm .... he thought passing me at 1 cable was enough ...

 

[srm]

Would an average private radar operator( or even a commercial ship operator) pick up the Op's return in a cluttered area, if it was moving at, say, 14 kts.( or whatever speed it does) Even if that return was fairly good.

Don't know about private operators as ability of the watch keeper, if any, is an unknown. However a commercial vessel will almost certainly be using ARPA (Automatic Radar Plotting Aid). If the target is providing a consistent radar return the system will track it and provide a warning to the OOW (Officer of the Watch) if the target is going to pass within a preset CPA (Closest point of Approach) or is a risk f collision (CPA= zero).

The problem for small vessels is the manoeuvrability and available sea room of the commercial vessel, and having just seen the post above by @Refueler, the level of training and seamanship of the OOW. Basically, the commercial vessel needs to see your vessel in enough time to plan and make an effective alteration to give a safe passing distance. I ran my last radar and electronic navigation simulator course for MN deck officers in 2010. At that time we expected candidates operating in open water to pass other vessels at one mile. However passing distances may have to be significantly less where the vessel is restricted by available water depth or other navigation hazards. If you are detected too late it may be physically impossible for the commercial vessel to avoid you due to momentum and the time it takes for the rudder to have effect.

The further away you can be detected by radar and/or AIS the better your chances of avoiding close encounters.
Incidentally, the passive radar reflectors on the market are only effective on 3cm band radars. Large commercial vessels generally run 10cm band radars but may also have 3cm band. On my last boat as well as the large passive reflector on the stern gantry and the usual smaller mast mounted reflector I had a dual band radar target enhancer at the mast head to avoid shadows and give max range so as to show in the 10cm band (for some reason we are not supposed to call them transponders). Having taught radar theory and practice I want to reduce the risks of not being detected in sufficient time.

 

[Alicatt]

I worked for Decca Radar as a trainee in the early 1970s, as part of my training I had to go to head office in Croydon to get a training course on digital logic and how it is implemented in radars as an anti-collision aid, built my first computer on that course, also while there I did training on MF & VHF radios, theory then installing and servicing them.
Radar has come a long way since then!

 

[Refueler]

"Incidentally, the passive radar reflectors on the market are only effective on 3cm band radars. Large commercial vessels generally run 10cm band radars but may also have 3cm band."

Sorry srm ... but I have to question that statement ..... All ships I have sailed ... all ships my company superintend now - ALL have 10 and 3cm Radars - with most having the main ARPA on 3cm. Of course I cannot state for all vessels - but at average of 50 - 60 vessels per month my company involves with ... I think that may be a fair value.

Second not all radars on the bridge are part of the ARPA network - I sailed with usually two radars on bridge - but many ships today have 3 or 4 .. with 1 or 2 under ARPA. Of course most will have a switch box so in event of failure or wish to swap radar for whatever job is possible.

That switchbox .. example : On the Gas Ships I sailed as OOW ... going north in Palawan Passage we would have main radar as #1 ... using #1 antenna. Going South on return passage - we would switch to #2 radar as main via #1 antenna ... #1 would then use #2 antenna. Yes this was unusual as most ships will not need or bother to do it ...

Many ships today actually have AIS integrated into the radar display as well .... so reliance on radar target return is lessened.

Times really have moved on ..

 

[Refueler]

I worked for Decca Radar as a trainee in the early 1970s, as part of my training I had to go to head office in Croydon to get a training course on digital logic and how it is implemented in radars as an anti-collision aid, built my first computer on that course, also while there I did training on MF & VHF radios, theory then installing and servicing them.
Radar has come a long way since then!

mmmmm can never forget one Decca Radar unit ... Shell actually had various of the L class vessel fitted with it for evaluation ... if I recall correctly - it was called : Situation Display radar ....

It had a small radar screen in the bottom of the cabinet ... a TV camera sat over it ... the video was then shown on a large TV screen at top of the cabinet. It was daylight viewable etc. The target would paint on screen as it moved - produced a 'line' of travel on screen.
It actually caused many an OOW to have some close shaves as the line drawn was True motion on a Relative motion screen !! Yes I know - some here may be questioning that bit - but true. It was a great idea .. but seemed to lack real thought in its implementation.

 

[srm]

"Incidentally, the passive radar reflectors on the market are only effective on 3cm band radars. Large commercial vessels generally run 10cm band radars but may also have 3cm band."

Sorry srm ... but I have to question that statement ..... All ships I have sailed ... all ships my company superintend now - ALL have 10 and 3cm Radars - with most having the main ARPA on 3cm. Of course I cannot state for all vessels - but at average of 50 - 60 vessels per month my company involves with ... I think that may be a fair value.

Second not all radars on the bridge are part of the ARPA network - I sailed with usually two radars on bridge - but many ships today have 3 or 4 .. with 1 or 2 under ARPA. Of course most will have a switch box so in event of failure or wish to swap radar for whatever job is possible.

That switchbox .. example : On the Gas Ships I sailed as OOW ... going north in Palawan Passage we would have main radar as #1 ... using #1 antenna. Going South on return passage - we would switch to #2 radar as main via #1 antenna ... #1 would then use #2 antenna. Yes this was unusual as most ships will not need or bother to do it ...

Many ships today actually have AIS integrated into the radar display as well .... so reliance on radar target return is lessened.

Times really have moved on ..

Thanks, as I said its quite a few years since I was actively involved. We had only been able to drop Decca from the course a couple of years before I retired as it had remained in use in a couple of parts of the world and AIS was the new kid on the block.

I think that its helpful if leisure boat operators can appreciate the limitations of larger commercial vessels, especially the need to plan course changes well ahead, perhaps before the small boat is aware that they are there.

 

[st599]

I later spoke to a radar expert who said that sometimes the sum of the 2 can be greater than each single reflector & that having 2 reflectors as I have is a good idea.

Did he also say that as well as constructive addition, it could cause destructive nulling? With 2, you can cause a larger signal, or no signal. All depends on angle, distance between them and wavelength.

 

[Refueler]

Thanks, as I said its quite a few years since I was actively involved. We had only been able to drop Decca from the course a couple of years before I retired as it had remained in use in a couple of parts of the world and AIS was the new kid on the block.

I think that its helpful if leisure boat operators can appreciate the limitations of larger commercial vessels, especially the need to plan course changes well ahead, perhaps before the small boat is aware that they are there.

The main thing for me - having been that poor sod on the brigde trying to figure out what the other is going to do ...... for people to not faff about ... make decision - make course change bold enough to be obvious ..... and keep to it ...

College Lecturer made a comment which at the time sounded a bit obvious - but is reality :

Collisions are because two idiots decide to be in same place at same time.

An old Master I sailed with in my first days :

Why pass close when you've got a whole bloody ocean to play in ??

 

[Greg2]

An active radar reflector apparently overcomes most of a passive radar's shortcomings, but at a cost not all can afford or tolerate, and is of course dependent on the continuous availability of a power supply (though rarely a problem on modern equipped boats). The model depicted in post #7 operates only on one of the two radar bands that ships might be using. Two band types are even more expensive. I've never been clear how much of a disadvantage the lack of the other band is. (Neither do I know how consistent (or not) the re-broadcast signal is around the 360 degrees horizon, or at different vertical angles fro the horizon.)

X band radar is required on all commercial ships over 300GRT and S band, which is better for longer range work, is required in addition to the X band on larger (I.e. ocean going) vessels. In reality I think most vessels under 300GRT will have X band as it is the better of the two for closer range.

I recently did an MCA electronic navigation/bridge watchkeeping course and ensuring that you were using X band was a factor when carrying out radar tasks inshore.

On a separate note, using AIS when dealing with collision avoidance is a big no because it is not reliable and information can be inaccurate.
.

 

[Refueler]

X band radar is required on all commercial ships over 300GRT and S band, which is better for longer range work, is required in addition to the X band on larger (I.e. ocean going) vessels. In reality I think most vessels under 300GRT will have X band as it is the better of the two for closer range.

I recently did an MCA electronic navigation/bridge watchkeeping course and ensuring that you were using X band was a factor when carrying out radar tasks inshore.

On a separate nite, using AIS when dealing with collision avoidance is a big no because it is not reliable and information can be inaccurate.
.

3 vs 10 .... age old debate between seagoers .... which is better ? Depends on the task in hand.

3cm suffers greater sea state clutter ... rain .... which can mask targets ... but has greater definition when a clean return.

10cm is less affected by sea clutter and rain - but has less definition especially when passing headlands etc - the elongation of the headland can be significant.

Most vessels carry both and in my experience / observation - 3cm tends to be the one most used.

As regards AIS ... depends how you use the AIS target data you get ... if you just rely on the information of speed / course relayed - then I agree with you ... especially when it comes from a yacht .. course / speed is at best a compromise. But if the ship has as most do today - AIS integrated into the radar display - then this is a different ball game altogether as the track can be determined better than if separate AIS or only radar .. each compliments the other in the integrated system.

But all this is digressing away from OP's original reflector post.

IMHO - whether a reflector works well or not - it must be better to have than not have. Any % gain over that of non fitting - is a gain.... even if small.

 

[LittleSister]

For the confused amongst us, Google tells me that -

X Band is 10 Ghz

S Band is 3 Ghz

 

[Refueler]

For the confused amongst us, Google tells me that -

X Band is 10 Ghz

S Band is 3 Ghz

Maybe ... but the BW is 3cm and 10cm

Its why 10 elongates headlands etc on display.

3cm requires waveguide
10cm uses cable.

 

[Refueler]

I disagree. There is severe doubt about the effectiveness of most of the passive radar reflectors of the sizes and types used on small to medium sized boats. Having one may or may not increase one's visibility to other vessels using radar, and may give the boat owner false confidence they are visible to other shipping.

I am not for a moment suggesting not having one, but cautioning against false expectations of how much, if any, additional radar visibility is actually being achieved.

The OP has a 25' motorboat.

The boat itself, and it's contents (especially e.g. engines), will reflect radar, but not necessarily strongly or at all consistently.

It is not actually impossible, but decidedly impractical to carry an effective-sized conventional passive radar-reflector on a boat this size or smaller. Size is extremely important in the amount of refection that can possibly be achieved, and the design (and correct orientation mounting) of the reflector is very important in determining how much of such potential reflection is actually achieved from different angles both from the heading of the boat and vertically from the horizontal as the boat is heeled or rolling.

In an attempt to overcome the size challenge, many sailing boats have a patent-array-in-a-drum type reflector mounted on the front of the mast, but these apparently suffer from being screened from a significant sector aftwards by the mast itself.

An active radar reflector apparently overcomes most of a passive radar's shortcomings, but at a cost not all can afford or tolerate, and is of course dependent on the continuous availability of a power supply (though rarely a problem on modern equipped boats). The model depicted in post #7 operates only on one of the two radar bands that ships might be using. Two band types are even more expensive. I've never been clear how much of a disadvantage the lack of the other band is. (Neither do I know how consistent (or not) the re-broadcast signal is around the 360 degrees horizon, or at different vertical angles fro the horizon.)

How visible you are, even with the best kit, will very much depend on the weather, how rough it is, the quality (or otherwise) of the radar gear in use by other vessels, and the settings the operators have applied to their gear.

Of course, in a big swell your boat and radar reflector of either type may well be screened from radar view a significant amount of the time, and hence not be picked up (see srm's post 20 above.).

One can only do what one can to increase the likelihood of radar visibility, depending on boat size/type, depth of pockets, etc. and hope for the best. Don't bank on always being seen, though!

All well and good ... but next time out on the oggin .... take a look at the buoys you pass used in shipping channels. Notice the reflector used ? Rain catchers.
As an ex OOW on Bridge - those buoys show up on radar .. even though they are low - often smaller than a MoBo ...

I do not say - reflector is always seen / good ... but if that MoBo should mount a rain catcher on top of its small mast as some do - he will be replicating what most buoys do.

 

[wonkywinch]

Maybe ... but the BW is 3cm and 10cm

Its why 10 elongates headlands etc on display.

3cm requires waveguide
10cm uses cable.

λ = v / f

where v = the speed of light (300,000,000 metres per second though it's common practice to round this value to 3 × 10^8 m/s).

10GHz is approx 3cm and 3GHz approx 10cm so both answers correct.

Reminded me of the twin temperature conversions stuck in my mind - 16C = 61F and 28C=82F.

 

[Refueler]

λ = v / f

where v = the speed of light (300,000,000 metres per second though it's common practice to round this value to 3 × 10^8 m/s).

10GHz is approx 3cm and 3GHz approx 10cm so both answers correct.

Reminded me of the twin temperature conversions stuck in my mind - 16C = 61F and 28C=82F.

Why making the point ... get into a chat with an operator and he will use the 3cm and 10cm terminology .. its standard 'speak' on the bridge ... radar courses ... service techs etc.