AIS net marker buoys

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pcatterall

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Have these any 'legal' application for leisure boaters?
I see that they are around £130 and can be programmed to display yacht details. They look robust and have long lasting rechargeable batteries.
I can envisage one going overboard with my danbuoy or even instead of it and it could augment my receive only AIS.
Are there different regulations concerning their use in different countries. I have not seen one displayed on our own AIS so perhaps they are not widely used?
 
These net buoys are considered illegal. Check them out. Moreover only for use to you as they probably do not convey that an urgent situation exists.
 
Not automatic. So if you use it as a AIS PLB on a dhan boy:

Needs switched on when chucked in water
Only updates every 3 mins
Type of message is an issue... But someone in deck knew of a mob to chuck dhan.

If you use on lifejacket:
Manual activate only works if conscious
Doesn't actively alert mothership that it has been activated
 
KompetentKrew said:
Looks like they come with the MMSI preprogrammed, which surely makes them illegal to use?
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Personal MOB AIS/DCS devices should not be programmed with the parent vessels MMSI, they should come with a pre-programmed MMSI chosen from a pool of MMSI's reserved especially for the purpose.

The current allocation is in the "972" prefix, in the format "972xxyyyy" where xx is a manufacturer ID, and yyyy is a sequence number. AFAIK, the sequence numbers are not unique.
 
UK made net marking buoys use AIS Aid to Navigation messages which means they are supposed to use a MMSI issued by the MCA/OFCOM and be static (permanent position approved by MCA/OFCOM). Because this can't be the case with a net, they are not legally allowed in UK waters. There is some work being done to get them approved but will take a few years.

Some of the Chinese made devices use the same message but transmit using the AIS search and rescue transponder access to the AIS broadcast which effectively stamps on all other AIS transmissions. The increased use of these by potentially thousands of net markers will block the regular transmissions and lead to AIS ranges being massively reduced.
 
A good solution would simply be to use low power devices ... reducing the power to 50 to 100mW would give coverage to around 1nm, more than enough for passing vessels to take avoiding action, and affect a very small area ... it's not rocket science.

Sadly, the spec as it stands makes no allowance for low power devices from what I can see ... it's either full "class B" or it's not in spec ...
 
rszemeti said:
A good solution would simply be to use low power devices ... reducing the power to 50 to 100mW would give coverage to around 1nm, more than enough for passing vessels to take avoiding action, and affect a very small area ... it's not rocket science.

Sadly, the spec as it stands makes no allowance for low power devices from what I can see ... it's either full "class B" or it's not in spec ...
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Yes I can see that limited range units on nets or pot buoys could be useful to both the fishing boat and yachtsmen (for avoidance purposes) but a proliferation of higher powered ones could be an issue.
 
rszemeti said:
A good solution would simply be to use low power devices ... reducing the power to 50 to 100mW would give coverage to around 1nm, more than enough for passing vessels to take avoiding action, and affect a very small area ... it's not rocket science.

Sadly, the spec as it stands makes no allowance for low power devices from what I can see ... it's either full "class B" or it's not in spec ...
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That doesn't work at all.
If you are close to a 100mW device, it will still block a 5W device at moderate range.
It would be far better to find another channel.
 
lw395 said:
That doesn't work at all.
If you are close to a 100mW device, it will still block a 5W device at moderate range.
It would be far better to find another channel.
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There is a lot of confusion about AIS in this thread and I think a lot of rubbish is being spouted about blocking transmissions.
For a start
Class B is 2W transmit not 5W!
Class A is 12.5W
Neither transmit at all times it is a very short digital pulse.
Class B transmissions can however be delayed by the priority given to class A.
Class B transmissions are a free for all there is no slot reservation so the loudest signal gets through.

These pot or net markers on class b are transmitting at a maximum of 2W about 2 inches from the water level on a very small antenna .

They are programmed not to transmit more than every 3 minutes.

This is the same as a Class A or Class B boat at anchor.

Class B the transmissions are every 30 seconds if you are doing more than 2 knots .

In contrast class A is every 10 seconds from moving to 15 knots and then progressively shorter to 2 secs if doing more than 14 knots.

I don't think these pot markers create a blocking issue of any significance. They do however create a different problem. They create a mass of targets on your screen that can't be called up on the VHF.

It would much better if the MMSI number or unit spelled out on our MFDs that it was a pot or net marker and was marking a tempory navigational hazard.
I can see that without this class A boats are going to start ignoring random uncontactable mmsi class b targets that come in and out of range with a slight swell and have zero radar profile.
I guess this could lead to a significant longer term problem with small class B pleasure craft being ignored in a similar way with a potential for loss of life.
 
12.5W is only 21dB up on 100mW.
A signal 6dB below the wanted will cause interference and errors.
15dB in range is about 5.6x.
So if you are close to some of these net markers, they can start interfering with ships within your circle of interest.

AIS is not, AIUI, particularly robust to corruption of messages. If these things are not respecting timeslots, your AIS receiver or plotter could display all sorts of rubbish. It doesn't take many of them to create a significant risk.
 
lw395 said:
That doesn't work at all.
If you are close to a 100mW device, it will still block a 5W device at moderate range.
It would be far better to find another channel.
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You don't get this RF stuff do you?

AIS can cope quite well with moderate traffic densities, by reducing the effective range of the not-very-important units you reduce the number of units in any receivers effective range.

Just how many net markers do you think you are likely to see in your local 1mile radius? For most of the UK, I would think the number would be "significantly less than one" and in busy areas with lots of net markers, it might be as high as 2.

I am willing to go out on a limb and state that the AIS system in most areas is not so fully contended that it cannot support another 2 additional devices in a typical receiving units range ...
 
lw395 said:
12.5W is only 21dB up on 100mW.
A signal 6dB below the wanted will cause interference and errors.
15dB in range is about 5.6x.
So if you are close to some of these net markers, they can start interfering with ships within your circle of interest.

AIS is not, AIUI, particularly robust to corruption of messages. If these things are not respecting timeslots, your AIS receiver or plotter could display all sorts of rubbish. It doesn't take many of them to create a significant risk.
Click to expand...

But that is how the system works, there will ALWAYS be stations interfering with other stations, for example .. assume the effective range is 10 miles, there is a vessel to your east, 8 miles away .. and a vessel to your west, 8 miles away ... you can "hear" them both, but the other two are unaware of each other ... and .. it doesn't matter! They will (occasionally) obstruct your reception of the other one. In busy areas this happens ALL THE TIME.

A large percentage of your reception is of messages that are being "clobbered" by other, louder, nearer messages. The louder, nearer ones get through, the more distant weaker ones do not. And that is absolutley fine, as the distant things are not what you care about most. If one transmission gets clobbered, randomisation of the timing ensures that there is a good chance the next one won't.
 
rszemeti said:
You don't get this RF stuff do you?

AIS can cope quite well with moderate traffic densities, by reducing the effective range of the not-very-important units you reduce the number of units in any receivers effective range.

Just how many net markers do you think you are likely to see in your local 1mile radius? For most of the UK, I would think the number would be "significantly less than one" and in busy areas with lots of net markers, it might be as high as 2.

I am willing to go out on a limb and state that the AIS system in most areas is not so fully contended that it cannot support another 2 additional devices in a typical receiving units range ...
Click to expand...

I think you may be wrong there.
These devices are dirt cheap.
There could be large numbers of them in some places.
I've heard of them being used for crab pot markers, not seen it myself though.
 
Dirt cheap as in £130 'cheap'?

Pot markers presumably on one end of a string of pots - how many strings in a 1mile radius though?

Can someone point me to where there are a load of these in a 1mile area... I figure they have a second hand value ;).

Not completely sure I understand what the use for them is! If I'm laying a string of pots why wouldn't I mark a WPT on my plotter? Why would the pots shift so much that when I get to the WPT I can't find them? Or is the aim to help sailors avoid them and so avoid lost tackle?
 
ShinyShoe said:
Dirt cheap as in £130 'cheap'?

Pot markers presumably on one end of a string of pots - how many strings in a 1mile radius though?

Can someone point me to where there are a load of these in a 1mile area... I figure they have a second hand value ;).

Not completely sure I understand what the use for them is! If I'm laying a string of pots why wouldn't I mark a WPT on my plotter? Why would the pots shift so much that when I get to the WPT I can't find them? Or is the aim to help sailors avoid them and so avoid lost tackle?
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Dirt cheap as in could be under $50 on alibaba..

There are not loads of them in the UK AIUI, but there would be a rash of them if they were legal.
So I very much doubt they will be made legal.
 
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