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  1. #11
    Blue5's Avatar
    Blue5 is offline Registered User
    Location : Hampshire and Portugal
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    Default Re: AIS class B transceiver

    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

  2. #12
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    Default Re: AIS class B transceiver

    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.

  3. #13
    Talbot's Avatar
    Talbot is offline Registered User
    Location : Stavanger, Norway
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    Default Re: AIS class B transceiver

    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. [img]/forums/images/graemlins/frown.gif[/img] 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.
    "Be wary of strong drink. It can make you shoot at tax collectors - and miss."
    Robert A Heinlein

  4. #14

    Default Re: AIS class B transceiver

    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?

  5. #15
    Talbot's Avatar
    Talbot is offline Registered User
    Location : Stavanger, Norway
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    Default Re: AIS class B transceiver

    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.
    "Be wary of strong drink. It can make you shoot at tax collectors - and miss."
    Robert A Heinlein

  6. #16

    Default Re: AIS class B transceiver

    [ 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?

  7. #17

    Default Re: AIS class B transceiver

    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.

  8. #18

    Default Re: AIS class B transceiver

    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

  9. #19

    Default

    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.

  10. #20
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    Default

    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.

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