AIS class B transceiver

[Blue5]

/forums/images/graemlins/confused.gifPost Ouzo and looking to see and be seen was considering an AIS class B transceiver but a few questions need an answer.

The more I look into it the more conflicting information I receive so please help

I understand that with the transceiver you need VHF and GPS aerial connections, I was told that VHF needs a separate aerial at least 4m away from your radio aerial to avoid interference.

Can you connect to existing GPS nmea feed

Anybody recommend a unit and any advice please

 

[shmoo]

They are not about to let you put your own GPS feed into a class B AIS tx - we won't be trusted to do it right. They will have GPS built in.

 

[Blue5]

Ok so it is just a separate VHF aerial connection, the GPS is part of the transceiver

 

[jonjo]

These are very new and very expensive at the moment. I doubt the effectiveness of a class B transceiver just now, how many merchant ships are equipped to present AIS info in a convenient and prominent location on the bridge?

 

[Talbot]

Yacht transceivers will only be allowed at low power settings. IMHO they will cause confusion with merchant ships cause they wont see them until quite close (if they see them then, and will give false confidence to the user. Furthermore, on a small yacht, they are a significant power drain.

However, a receiver, especially when it provides a cpa system and an audible warning of those tracks perceived to be a problem, adds a very valuable tool to the small boat mariner.

Claiming that this or that tool would have saved the lives of somebody is an intolerable intrusion into the grief of the relatives and in most cases cant really be proven either way.

 

[bilbobaggins]

Maybe you'll find the right quality of advice here at SeaSolutions

Let us know?

/forums/images/graemlins/grin.gif

 

[tome]

Have to take issue with your understanding of Class B transponders. They will be limited to 2W power output, but even so this should provide a useful range up to 20M. As for power drain, the duty cycle of the transmitter will be no greater than 1:67,500 or equivalent to 2.5 micro amps so no significant drain even on the smallest yacht

On the question of whether it would have saved Ouzo lives, I don't see any reference in the OP so don't understand your rant into intrusions etc. The poster was merely refelcting (IMO) on what further steps to take to improve viz in light of the incident

 

[tome]

I haven't yet looked at any commercial class B transponders, except that I have the specifications and have studied these. However, it's entirely probable that you will connect it to an external GPS feed as you do with a DSC radio

A rail mounted VHF antenna will give more than adequate line of sight to a bigger vessel. I have such an arrangement for my AIS receiver and have seen some targets at almost 40M range

Class B AIS will transmit at 2W and a maximum rate of 30 secs. It transmits an abbreviated message (no rate of turn, nav status, IMO number, destination etc). The method of operation is slightly different from Class A in that it doesn't have any assigned slots. This means that it has to try to locate a free slot when its 30 sec interval comes around. If it cannot find a free slot, my understanding is that it skips the current message. The upshot of this is that you definitely (IMO) want to go for a dual frequency unit where the chance of missing a reporting slot is halved

 

[Channel Ribs]

You make a good case, and I want to AIS B, but I can't help feeling that it comes out pretty low on the list of essential safety gear.

 

[tome]

Agree for the time being. But then, where would you put it on a sliding scale versus a See-Me?

 

[Blue5]

Thanks Tome it gives me a much better understanding.

Also Talbot. an alarm set up would be a first indication of possible trouble

I take the points made by other replies but one post on safety gear that stood out some time ago for me was that money was better spent on prevention of the accident than the epirb so they could find you after it happened.

We all want to sail in safety without incident and I am just looking at what else is available to tilt the balance in my favour

 

[ParaHandy]

the thing you have to remember is that few commercial vessels carry Class A AIS interfaced to their navigation/radar system. Most have the bare IMO minimum which is a very small screen which just displays the messages received and which quickly scroll off their screen.

 

[Talbot]

2w power, but where is the aerial. It cant be up the mast otherwise everytime you transmit on vhf, there is a good chance of bleed through to the AIS receiver. so it will end up on the pushpit. What is the range of vhf when the aerial is only 2m above sea level - well that will depend on the receiving aerial, but between 5-7 miles. modern merchant travelling at 20 knts looking at the display abt once every 30 minutes? - it will only take 20 minutes to travel to you. /forums/images/graemlins/frown.gif I rest my case.


And in any case, I much prefer knowing where they are before they know where I am, so that I can manipulate CPAs enough so that I dont have to rely on a merch changing course, that way I feel more in control of what is going on.

 

[tome]

Sorry Talbot but you're way off, and scaremongering what could prove to be a very useful emerging technology for us in the future

You conveniently ignore the persistance of AIS acquired target data and the potential for bridge alarms. And if you think a merchantman travelling in narrow waters only checks displays every 30 mins then you've never been near the bridge, have you?

 

[Talbot]

who was talking about narrow waters - not me - and yes I would hazard a guess that 14 years of watchkeeping at sea all round the world would probably give me some knowledge.

 

[tome]

[ QUOTE ]
I would hazard a guess that 14 years of watchkeeping at sea all round the world would probably give me some knowledge

[/ QUOTE ]

Was this Andrew perchance, and were you a navigation officer?

Think we were discussing merchant ships, no?

 

[EDM]

NDH - your initial question was one of "Considering an Active AIS".

As the previous threads have stated AIS-Class B will be reduced power, and that therefore implies reduced range. 2W TX power as long as you are using good quality coax and a well situated antenna will still send a signal a long way.

The amount of RF problems from 2W radiated power into your GPS, VHF, Navtext - all rather depends upon how well they have been fitted, as well as antenna placement. If you want a quick test use a Marine Handheld (5W) next to your GPS - I would be surprised if any problem. Repeat with your larger VHF.

With AIS-B being rather a new technology, the AIS-B data sentence (sent out from your Black box to a plotter/pc etc) may not be understood by older software packages/plotters; So you may have to buy another new shiney plotter. I am however not 100% sure if the sentances are difference formats, or the same with empty fields. {Can anyone please point me to the Specs for EC62287 draft Class B}

Class B will not have SOTDMA ( Self-Organized Time Division Multiple Access) - which Class A has. This functionality stops Ships (or other stations) transmitting at the same time. This will mean that should you be sailing with 2250 other yachts someone may not get your position.

I currently do not have Active AIS, but it is on the list - Before See-Me.

 

[tome]

Class B still uses the same time slot structure, but a different access method known as Carrier Sensed TDMA which also stops other stations transmitting at the same time. Therefore there won't be any difference between reception of Class A or B at the receiver except that Class A has transmission priority.

The max number of transmissions possible is 2250 so it's feasible that areas like the Solent may experience overload, when class B equipment will start to drop out - or at the least the update rates will be reduced as slots are missed

AIS B sentences will conform so no need to upgrade plotters etc

 

[waltonsboater]

I would think that anything to help other vessels to see me would be a benefit.
Like an EPIRB it's a bit of kit that I would never rely on, on its own - however if the worst were to happen, I would like to know that other vessels, the lifeboat, the coastguard and helicopters could see where I am.

 

[Ex-SolentBoy]

Surely anything that helps others see/detect your vessel is a good think from a safety standpoint?

Whether something is affordable, practical to install, aesthetically pleasing etc. is down to personal choice.

I am a wimp. I have a Sea-Me and a Comar CSB 200 Class B AIS. We have a separate VHF aerial and separate GPS aerial to feed the AIS. Interestingly, having taken advice from the aerial manufacturer we mounted the aerial for the GPS under the cockpit coaming in the lazarette locker. There is it out of the way from the elements and potential knocks.

You may think that the reception was harmed in some way, but I was very suprised. The GPS locked onto a full range of satellites even when the boat was still in the factory!

For similar reasons we put the VHF for the AIS in there. Yes, it is low down, but we still see vessels 20 plus miles away, and they can see us (I have checked with them). More than enough range for me from a safety standpoint.