AIS Class A & B v Radar

[benjenbav]

Picking up on hurricanes point re fog and night passage that would be the only time we would use radar.

We came back from Guernsey a few years ago and ais would have been very welcome as the sea fog rolled in 

Q:what do you do when it's too splashy to see out of the front window? A: put the kettle on and drive by the radar.

I would seriously suggest a screen that can handle inputs from radar and ais. Then you are just paying for the black box bits to add these items.

 

[Trundlebug]

As said above, radar and AIS are different animals and have different uses.

As I already had radar but no reflector, for me the choice was AIS transceiver or radar reflector.
That's a much more difficult decision.
In my case shortage of space to fit a large reflector (the small ones are as good as useless - and I don't have the space for token gesture ornaments posing as safety kit) made the choice therefore between fitting an active radar reflector or AIS Transceiver.

After much deliberation I chose AIS transceiver, and haven't regretted it although I wouldn't criticise anyone who chose active radar reflector.
It is after all a requirement of the colregs to have one.
My conclusion was that AIS transceivers weren't invented when the colregs were drawn up, and are the modern solution to the same problem of making a vessel visible to other traffic.

I'm aware of the argument made above about large ships filtering out AIS B reception in heavy traffic areas, but my cruising ground isn't in the Solent and provided I maintain my awareness of that possibility, the numerous other benefits of AIS outweigh that one potential weakness.

 

[ian38_39]

Just going through exactly the same thought process. Have been assured that class B is not screened out but that the signal is seen less often than class A, maybe every 45 seconds instead of every 10.

Had Radar on our last boat and the only time in 7 years I needed it it decided not to work, survived the incident by using common sense and a plotter.

Have 4 plotters aboard, 2 having internal power supplies and internal GPS receivers, short of a lot of satellites falling out of the sky or switching themselves off I am pretty confident that I can confirm my position to within a few feet.

Entering a harbour at night, or in fog would mean keeping a careful watch on the plotter and the surroundings but I would trust myself to get that right more than relying on radar that I use once every 5 years

I think there already are buoys that transmit an AIS signal and this can only get more widespread and I'm guessing it won't be long before a simple transmitter is available very cheaply for small boats, it would be a lot more effective than a radar reflector.

 

[Hurricane]

I think there already are buoys that transmit an AIS signal and this can only get more widespread and I'm guessing it won't be long before a simple transmitter is available very cheaply for small boats, it would be a lot more effective than a radar reflector.

Just been reading the latest OpenCPN software development history for the current beta test version.
It seems that these buoys that transmit AIS fall into a category called AIS AtoN - Aids to Navigation.
Not sure how this fits in with this thread but it shows how extra facilities are being built on the success of AIS.
I wish that the people who designed DSC had had the same forethought - now there's a system (DSC) that seems to be a complete waste of space.

 

[Trundlebug]

Yes there are 2 kinds of AIS AtoNs.

There are real buoys which also transmit AIS
There are also virtual buoys. There is one off the SW coast of Britain somewhere, where a buoy was repeatedly getting damaged by ships hitting it. So they (Trinity House) removed the physical buoy but still transmit AIS from that location - a "virtual" buoy.

I was told this by the captain of THV Patricia a couple of years ago

 

[Jurgen]

Q:what do you do when it's too splashy to see out of the front window? A: put the kettle on and drive by the radar.

Drive from the flybridge and get wet lol

 

[Bandit]

Further to my post above.

Lots of fog in CI, there are lots of Liesure boats with out AIS, fishing boats turn off AIS when fishing, a lot of ships ignore yacht AIS.

There are many passages when it's rough where you can't see well out of the windscreen so rely on plotter and radar.

You can't see pier heads on AIS in fog or small boats.

AIS is not a replacement for radar, it is a nice thing to have as well as radar.

 

[gjgm]

Would do the occasional Chanel Island trip but 99% of boating is in the Solent


What are folks thoughts?

Then 99pct of the time AIS is useless.
No, that is not quite fair, but in the Solent you will never ever have the alarm on as it never stops. Including in the marina.
I like AIS in the Channel- ships and Condor ferry. I would get AIS receive as it is so cheap, why not. You could also consider the active radar return systems (£350).
Comments on rocks and radar.. out of interest they are on the plotter and don't move much...?

 

[maverickofpoole]

If I never fished or went across the channel I would prefer radar as you can hopefully spot all craft without ais but when going offshore ais just makes things so much easier when looking out for larger craft.
Earlier someone said that a lot of shipping ignore class b ais although on my previous boat I was called up by name by a ship going up the English channel to clarify we had seen him which we had. If that ship had ignored class b and only used the radar they would not of called us by name and I would have probably ignored their call as we would have been too busy fishing to process/acknowledge a position call. My new to me boat has radar but not ais (nor autopilot ) but that is on my todo list when she is hauled out in February.

 

[Hurricane]

Further to my post above.

Lots of fog in CI, there are lots of Liesure boats with out AIS, fishing boats turn off AIS when fishing, a lot of ships ignore yacht AIS.

There are many passages when it's rough where you can't see well out of the windscreen so rely on plotter and radar.

You can't see pier heads on AIS in fog or small boats.

AIS is not a replacement for radar, it is a nice thing to have as well as radar.

Agreed
My comments were in based on Med experiences.
We used to do our boating in the Channel.
Entirely different - radar definitely more useful in UK waters.

 

[prv]

There is little point in overlaying radar over the plotter as a navigation aid.
It isn't that accurate anyway.

It's accurate enough to show that the chart and position on the plotter are correct. It's a constant comparison, performed visually, between position obtained by GPS and position obtained by bouncing radio waves off things. Without that cross-check, in poor visibility you'd be navigating on a single source of information, which is something I try never to do.

Pete

 

[Divemaster1]

Not going to weigh in on the discussion about which one is "best" as it depends on cruising area and use of the boat.... However, I am surprised about how many admit to have radar and never switching it on ....

Now you have a boat with this nice piece of safety kit ... often costing thousands of pounds (ours cost over £3,5K several years back)... and not using it ??

How do you know it will work when/if you need it ... and are you familiar with its operation, adjustments in the dark etc.?

I obviously have a very different routine to the majority on here ... and perhaps taking the COLREGS too serious about keeping a lookout with all available means ...

My routine is..

1) remove excess mooring ropes
2) Check engines etc.
3) Start engines and monitor
4) Switch on plotter, VHF and Radar
5) Disconnect shore power
6) Check that Radar and Plotter are functioning
7) let go of last mooring ropes and leave berth

Radar is switched off as one of the last things before engine shut-down ... or as approaching lock.... as per local rules...

I know that it works, I am familiar with its functions and will not be caught out by unforeseen events underway... Basically, I have it, paid for it and the use of it does not cost me any any more money... so why not?

 

[Bandit]

Further to above.

i believe that if you have radar fitted you are obliged to have it turned on and keep a watch on it. I might be wrong?

personally in fine conditions when on fly bridge I turn it off as I don't want my brain more addled than it is.

However when driving from saloon I run the radar so I am familiar with operation of the radar and can see that the the radar picture is confirming what I see with Mk 1 eyeball, so that in fog I am familiar with its use. It's no good having a radar that you use once a year and in anger if it's not second nature to use.

I also have one screen gor radar (head up) and another for plotter which is north up, a luxury I know but I like it.

 

[Divemaster1]

...........personally in fine conditions when on fly bridge I turn it off as I don't want my brain more addled than it is .........

That's why I ensured that arch was raised (from 4' to 6' when we had a "small" incident resulting in a replacement .... some boats does have less than ideal designs IMHO as arch is far too low ... form over function I believe...

 

[Piers]

AIS is good but it doesn't replace radar imho. There are plenty of things you can hit that are not transmitting AIS. You don't usually need radar in good weather and daylight but if you contemplate night running then AIS is nowhere near a substitute for radar imho.

I completely agree. Whilst AIS is useful 'as an aid' and can be 'fun' to know a target's details, radar is vital not the least in restricted vis. Play d'eau has a radar that displays AIS as well and it's interesting how much the AIS signal can lag behind the radar return given the AIS transmission delays.

As an aside, we always travel with our radar on not the least to practice so we aren't worried when in fog - as often happens in the Channel Islands and around the Finistere Peninsula.

Both chart plotter and radar are set to North Up - is this another debate?

 

[Talulah]

I obviously have a very different routine to the majority on here ... and perhaps taking the COLREGS too serious about keeping a lookout with all available means ...

i believe that if you have radar fitted you are obliged to have it turned on and keep a watch on it. I might be wrong?

Collision Regs was changed a while back to add the wording 'all available means appropriate in the prevailing circumstances and conditions'

On the subject of AIS v Radar. If you are someone who never goes out if Fog is in forecast then AIS (preferably transponder) everytime.

On a side note. Upgrading from analogue radar to digital radar was like chalk and cheese. (Upgraded C70 to C95) I don't recommend touch screen for in the cockpit on yachts. It becomes a pain in the neck once rain drops hit the display.

 

[Piers]

Collision Regs was changed a while back to add the wording 'all available means appropriate in the prevailing circumstances and conditions'

On the subject of AIS v Radar. If you are someone who never goes out if Fog is in forecast then AIS (preferably transponder) everytime.

When writing the articles on radar for MBM, I met with the GC and MAIB. Both said that radar, if fitted, had to be on, regardless "Proper use shall be made of radar equipment if fitted and operational". When were the COLREGs changed? I'd like to establish if this changes their understanding.

Re AIS v Radar, first can I ask what you use it for in good vis? Second, fog doesn't have to be forecast. If you cruise the Channel Islands, fog can happen very suddenly - most inconsiderate if it's not been in the forecast!

 

[Talulah]

When writing the articles on radar for MBM, I met with the GC and MAIB. Both said that radar, if fitted, had to be on, regardless "Proper use shall be made of radar equipment if fitted and operational". When were the COLREGs changed? I'd like to establish if this changes their understanding.

Re AIS v Radar, first can I ask what you use it for in good vis? Second, fog doesn't have to be forecast. If you cruise the Channel Islands, fog can happen very suddenly - most inconsiderate if it's not been in the forecast!

The collision regs were last updated in 2003.
pdf here http://www.collisionregs.com/MSN1781.pdf
Rule 7 relates to 'Risk of Collision'
Paragraph a) Specifically states the bit about approriate in the prevailing circumstances and conditions.
Paragraph b) is the bit in your response about proper use shall be made of radar equipment.
Some people may interpret proper use as 'on all the time' but I would suggest otherwise. Proper use would be more about range, which band, tracking etc. Trained operator etc

Re: AIS v Radar.
Whilst unforecast fog may appear very suddenly in the Channel Islands (an area I know you spent a great deal of time in) For the 'Solent Sailor as per the OP' radar is way down the list. If I was based in the Channel Islands I might switch my preference.

 

[Piers]

The collision regs were last updated in 2003.
pdf here http://www.collisionregs.com/MSN1781.pdf
Rule 7 relates to 'Risk of Collision'
Paragraph a) Specifically states the bit about approriate in the prevailing circumstances and conditions.
Paragraph b) is the bit in your response about proper use shall be made of radar equipment.
Some people may interpret proper use as 'on all the time' but I would suggest otherwise. Proper use would be more about range, which band, tracking etc. Trained operator etc

Hi Talulah. I see I wrote the article in 2005. Here's an extract:
-----
Is radar only for use in restricted visibility?

Five COLREGs specifically refer to radar - 6(b), 7(b) (c), 8(b), and 19(d), some using the word ‘operational’ which many boaters interpret to mean ‘would work if it was turned on’.

I asked the Maritime and Coastguard Agency (MCA), the enforcement body for the COLREGs in the UK, whether the word ‘operational’ meant ‘a working set which must be turned on’ rather than ‘a working set if it happens to be turned on?’ The MCA’s Navigation Manager replied,

‘Of course, in the context of Rule 6, ‘operational’ means working and turned on and working, (otherwise one that was not turned on would be a major characteristic under 6(b)(i)).

‘If it is turned off, it might as well not exist and you cannot include the radar on board within consideration of safe speed in accordance with Rule 6. Additionally if you have radar in circumstances where it could be of value such as in restricted visibility and then decide not to turn it on or use it, you could be in violation of Rule 2 and/or Rule 5.’

In other words, always on.

Furthermore, case law shows that if your craft is fitted with a radar you must use it and by implication know how to use it to its full potential for the conditions you are experiencing.

Remember that radar is not only for looking ahead, it also sees what’s coming up behind...
---------

 

[Hurricane]

Re AIS v Radar, first can I ask what you use it for in good vis? Second, fog doesn't have to be forecast. If you cruise the Channel Islands, fog can happen very suddenly - most inconsiderate if it's not been in the forecast!

AIS/Radar in good vis
We use both AIS and Radar for collision avoidance - we never use it for nav (as said above) - and I suspect that very few people do.
When approaching a collision situation we plan in advance what to do (alter course - change speed etc)
Under these circumstances, we use both AIS and Radar.
AIS is far more accurate under these circumstances.
Radar's MARPA requires a good fluxgate compass and even then it can't accurately predict the CPA - remember angular measurements with radar are carp.
OTOH AIS is getting exact data from the target vessel and you get a clearer more accurate picture.

But if there is a chance of bad vis, IMO radar would be the better system to have on board.
We have cruised the Channel Islands and in thick fog so I understand the concerns in UK waters.
But this isn't the case in other waters.
The UK with its more congested shipping and difficult weather conditions presents a totally different challenge.
In the Med, there is far less traffic and we just don't get bad vis.
Since arriving in the Med 7 or 8 years ago, I can't think of a time when our radar was absolutely necessary.
Yes, in the Med we do use it at night but we could manage without it.

We spent most of August cruising round Menorca and Mallorca.
Apart from the passages to and from the Baldricks, the radar was actually switched off.

EDIT
Here's a photo of a typical collision avoidance situation.
This is an AIS view of the situation showing the CPA
Radar would never be able to produce a view as accurate as this