AIS Transponders for Yachties

[RobbieW]

The following cut and pasted from Wikipedia, so not gospel. However it illustrates the differences between Class A and Class B, also gives a possible explanation for the dissapearance of Class B targets - if all slots were to be busy for long periods, the CSTDMA based Class B transmitter would never find a suitable slot.

That argues for installing a SOTDMA based Class B item, but anyone know whether there is a price penalty for doing so?

Class A
Vessel mounted AIS transceiver (transmit and receive) which operates using self-organised time-division multiple-access (SOTDMA). Targeted at large commercial vessels, SOTDMA requires a transceiver to maintain a constantly updated slot map in its memory such that it has prior knowledge of slots which are available for it to transmit. SOTDMA transceivers will then pre-announce their transmission, effectively reserving their transmit slot. SOTDMA transmissions are therefore prioritised within the AIS system. This is achieved through 2 receivers in continuous operation. Class A's must have an integrated display, transmit at 12 W, interface capability with multiple ship systems, and offer a sophisticated selection of features and functions. Default transmit rate is every few seconds. AIS Class A type compliant devices receive all types of AIS messages.[19]

Class B
Vessel mounted AIS transceiver (transmit and receive) which operates using, either carrier-sense time-division multiple-access (CSTDMA)or SOTDMA; there are now 2 separate IMO specifications for Class B. Aimed at lighter commercial and leisure markets. CSTDMA transceivers listen to the slot map immediately prior to transmmitting and seek a slot where the 'noise' in the slot is the same or similar to back ground noise, thereby indicating that the slot is not being used by another AIS device. Class Bs transmit at 2 W and are not required to have an integrated display: Class Bs can be connected to most display systems which the received messages will be displayed in lists or overlayed on charts. Default transmit rate is normally every 30 seconds, but this can be varied according to vessel speed or instructions from base stations. The Class B type standard requires integrated GPS and certain LED indicators. Class B equipment receives all types of AIS messages.

 

[jay]

erm . . . this asumes that the ship has seen you, either visually or on radar or on AIS or a combination of these.

I have called up a ship at a distance of half a mile because I thought they had not seen us. I was right; the OOW did see us when he looked out of the window while talking to me, but had not seen us on radar in the 4m swell. He appreciated my call and warned us about another ship on the same track a few miles behind that we could expect a close encounter with. This enabled me to call this second ship up by name when we sighted her. She was also grateful for the call as she had not seen us either.

The OOW does not have a clue what to do about targets he cannot see, except of course assume that they are not there . . . . you should never assume that a ship is aware of your existence, though an AIS transponder greatly increases the probability that it has.

People who leave their AIS transponder on in crowded inshore waters where the screen is a mass of targets, or in marinas, should ask themselves what exactly they think they are achieving.

- W

If you dont belive the ship has seen you then Rule 17 would apply - unless of course your in a TSS. Im a great believer in the use of technology and gadgets but at the end of the day if you follow the col regs you wont go far wrong. In my experince ships that arent keeping a good look out are probably the ones that when called on VHF have a very poor command of English anyway!

 

[johnphilip]

How to spread the word

Several posters seem to agree that AIS transmissions by leisure craft should only be made at night, in fog or in shipping lanes.
How could this become normal practice in the wider fraternity?
We need an evangalist

 

[DJE]

How far from the coast was the Ouzo hit?

Strictly speaking I don't think that was ever proven, but I take your point.

 

[Conachair]

Any views ?

A few... from a receiver only owner..


I've also watched ships turn 5 miles away to give me sea room mid ocean, and nice it is too But that's from radar, how does it work on big ships, is ais plumbed into the main display?

Not sure if I would upgrade to trasmit, knowing that with a steel boat the boys who matter should have me on radar anyway.

I don't pay quite so much attention to the reciever closer to shore, handy maybe to know that fishing boat has nets down if it's only doing a few knots but somewhere like the solent it's much more eyeball.

 

[RobbieW]

...But that's from radar, how does it work on big ships, is ais plumbed into the main display?...

Depends on the ship, there is no requirement for AIS to be integrated I believe. At one end ships have fully integrated navigation and control systems, at the other AIS is a stand alone box in the corner of the bridge.

I still believe RADAR to be the lowest common denominator in non visual collision avoidance so have taken steps to be as visible as possible to both X and S band.

 

[Blue5]

You'll be lucky, never seen a fishing boat on AIS yet

 

[PaulGooch]

You'll be lucky, never seen a fishing boat on AIS yet

Same here.

 

[Conachair]

You'll be lucky, never seen a fishing boat on AIS yet

http://marinetraffic.com/ais/

Deselect the other noise and even on a sunday there's a load out. Round english channel where I had a quick look anyway. Not sure if many of the little guys transmit but a lot of the bigger boys seem to do so now. All handy info when it's available.

 

[Blue5]

http://marinetraffic.com/ais/


All handy info when it's available.

Absolutely agree, I would like to see everything on the water transmitting information, it just needs a different thinking dimension about displaying the information on a screen so individual craft don't look like small islands on the display and frighten all the Solent sailors

 

[lenseman]

The issue is CLUTTER.

You can turn of AIS Alarms (because you normally can't decide not to have an AIS B trigger the alarm - so you have to turn both off - not really an issue in the solent though) ... but if you've got a raft of AIS B targets on your plotter screen it just obliterates the chart - you're not interested in the targets as you use line of sight - but you can't use the chart either - because theres a green blob on it. So your choices are - turn of AIS altogether or ignore/turn off the plotter ...

Here's an example from RTIR last year:

You know, I can't help thinking that you are a little niffed as you are no longer able to use your chart plotter as you would like?

About 8 or more years ago you probably went out and bought a wonderful new bit of kit called a chart plotter, set it up and looked in wonder at its display. You no no longer needed to look at a paper chart it was all there in front of you at the helm.

About this time AIS was being introduced and you had an AIS receiver installed. This meant that you could now see large shipping tens of miles away all displayed on your nice chart plotter. Absolutely brilliant, wonderful kit kit.

Then things starter to go wrong, AIS 'B' became available to the richer members of the leisure marine market, AIS 'B' transmitters were costing about £1500. Not so bad you thought, I can still see the BIG ships with the occasional expensive yacht which you didn't much care about.

As the years went by, the cost of AIS 'B' came right down and even poor yachties could now afford them. Not only that, yacht training schools had to fit the by law as they are commercial vessels and commercial vessels have to transmit AIS so Sunsail fitted them to all their fleet as did all the ferries. Fishing vessels have to fully comply by 2014.

Now what this means is that your once pristine chart plotter with which you could see all of the Solent, and some, was getting rather cluttered and you don't like it. You want to see a clear electronic chart and a few BIG ships.
You don't think it is fair that common yachties can be allowed to desecrate the display on your chart plotter.

I can assure you that soon, in not too many years it will be mandated that ALL sea going vessels will have to carry AIS 'A' or AIS 'B' dependent on size, whether they are commercial or leisure.

It is already compulsory that ALL yacht entering Singapore have to have AIS 'B' and it has to be turned on. Other countries are looking into this and will implement this in the near future!

If you don't like the clutter either turn off your chart plotter, or turn off your AIS receiver and you won't have any more clutter and you can sail on using the chart plotter as you main navigational aid.

The above is a bit tongue in cheek but it is much nearer the truth than you will care to admit?

 

[CelebrityScandel]

...It is already compulsory that ALL yacht entering Singapore have to have AIS 'B' and it has to be turned on...

In fact ANY IMO AIS transponder OR a HARTS.

Visiting yachts can hire a HARTS if needed.

 

[RobbieW]

...I can assure you that soon, in not too many years it will be mandated that ALL sea going vessels will have to carry AIS 'A' or AIS 'B' dependent on size, whether they are commercial or leisure.

It is already compulsory that ALL yacht entering Singapore have to have AIS 'B' and it has to be turned on. Other countries are looking into this and will implement this in the near future! ...

However that smacks far more of national security than safety at sea. I know its been possible to electronically track us since we got ATM cards but the 'big brother' principle is alien to many in a country where we still dont have to carry ID as we go about our daily business.

 

[BruceDanforth]

I saw another boat last weekend off the Northumberland coast.

 

[lenseman]

I saw another boat last weekend off the Northumberland coast.

It must have been one of those Viking long boats?

 

[DJE]

I can assure you that soon, in not too many years it will be mandated that ALL sea going vessels will have to carry AIS 'A' or AIS 'B' dependent on size, whether they are commercial or leisure.

And if there happens to be an Olympics on, or an American warship visiting, look out for the LNTM saying any vessel not transmitting AIS will be considered to have committed a hostile act....

 

[ianj99]

another toy for yachties, .

Especially on a motorboat on Loch Lomond I spotted on MarineTraffic last week.

I guess it was a visitor hauled there by RangeRover (it was a 30' motor boat) but why even have it switched on!

 

[maby]

Especially on a motorboat on Loch Lomond I spotted on MarineTraffic last week.

I guess it was a visitor hauled there by RangeRover (it was a 30' motor boat) but why even have it switched on!

Probably forgotten it is there, or not sure how to switch it off. For that matter, how do you turn the transmit off? We only have an AIS receiver fitted - there is no functionality on our plotter to turn a transmit function on and off. I'm guessing that a black-box transponder has a switch somewhere on the casing, but surely most people would mount it somewhere in the electronics compartment where it is not accessible without the aid of a large screwdriver?

 

[PaulGooch]

Probably forgotten it is there, or not sure how to switch it off. For that matter, how do you turn the transmit off? We only have an AIS receiver fitted - there is no functionality on our plotter to turn a transmit function on and off. I'm guessing that a black-box transponder has a switch somewhere on the casing, but surely most people would mount it somewhere in the electronics compartment where it is not accessible without the aid of a large screwdriver?

If it's a black box transceiver i'd expect there to be a flying lead for the "silent mode" switch to be connected to.

 

[fireball]

You know, I can't help thinking that you are a little niffed as you are no longer able to use your chart plotter as you would like?

Nope - I can still use it as I like because it won't display class B - I just haven't updated the software - the screen grab was from my phone!

About 8 or more years ago you probably went out and bought a wonderful new bit of kit called a chart plotter, set it up and looked in wonder at its display. You no no longer needed to look at a paper chart it was all there in front of you at the helm.

Rather patronising don't you think? "looked in wonder" ... bolx - I did go and get a chartplotter - and I'm happy with it ...

About this time AIS was being introduced and you had an AIS receiver installed. This meant that you could now see large shipping tens of miles away all displayed on your nice chart plotter.

"had an AIS receiver installed? Do you not read ANY of my posts - I installed the kit myself! Some of us are a little more than capable of doing so - as well as understanding the technology that it utilises - but carry on - talk down to me ...

Then things starter to go wrong, AIS 'B' became available to the richer members of the leisure marine market, AIS 'B' transmitters were costing about £1500. Not so bad you thought, I can still see the BIG ships with the occasional expensive yacht which you didn't much care about.

As the years went by, the cost of AIS 'B' came right down and even poor yachties could now afford them. Not only that, yacht training schools had to fit the by law as they are commercial vessels and commercial vessels have to transmit AIS so Sunsail fitted them to all their fleet as did all the ferries. Fishing vessels have to fully comply by 2014.

Now what this means is that your once pristine chart plotter with which you could see all of the Solent, and some, was getting rather cluttered and you don't like it. You want to see a clear electronic chart and a few BIG ships.
You don't think it is fair that common yachties can be allowed to desecrate the display on your chart plotter.

Now all this means is that my chartplotter with limited screen space is limited in its usefulness as I am only really interested in the big boys and knowing where I am/going - instead - should I choose to upgrade the plotter - I'd have to turn off the AIS receiver when sailing in places like the solent as it would become one mass of yellow blobs

I can assure you that soon, in not too many years it will be mandated that ALL sea going vessels will have to carry AIS 'A' or AIS 'B' dependent on size, whether they are commercial or leisure.

Is this a prediction?

It is already compulsory that ALL yacht entering Singapore have to have AIS 'B' and it has to be turned on. Other countries are looking into this and will implement this in the near future!

sounds like you're concerned about it now ...

If you don't like the clutter either turn off your chart plotter, or turn off your AIS receiver and you won't have any more clutter and you can sail on using the chart plotter as you main navigational aid.

if you read above you'll see that I don't have to worry - for now at least ...

The above is a bit tongue in cheek but it is much nearer the truth than you will care to admit?

ah - you're joking ... nowhere near the truth though ...

I have little issue with AIS B transponders - although I believe them to be of limited use in crowded waters - The issue I have is with the way that plotters treat the data feed - the inability to treat A & B as separate groups and no ability to suppress the display of B targets ...