Crikey, this is an old thread!
Crikey, this is an old thread!
I have just fitted a class B unit both for receive and possible assistance that I can get from the broadcast side. I accept it may not be perfect but who knows - it might help a merchant ship see me even if late in the day.
If they do spot a yacht and want more info, then they know just where to get it. Which has to be a good thing.
Three years on and we have still not fitted it to any of our boats, as I said back then there are other things above it on the list.
regards David - DSW Marine Engineering
[QUOTE=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]
I agree power drain is not a major issue but the average transceiver uses about 0.5 Amps in transmit mode and 0.2 Amps in receive only mode.
More to the point a friend of mine is a Thames pilot so he sees the bridges of more big ships than most and he confirms that only a minority of ships have their AIS receiver linked to their Radar/Nav screens. For most it is a minimum keyboard device at the back of the bridge which they consult only when they want the MMSI of a target they have aquired on radar.
If you can afford both an AIS transceiver and a radar transponder fine. However, if its a question of one or the other why spend money on a transceiver you know will only be seen by a minority of ships when you could spend less on a radar transponder that will will be seen by the majority?
Since I crossed the channel with you a couple of years back I am confident in your judgement at sea and in this case (not always, that's asking too much!) I agree with you entirely. My philosophy on a boat is much the same as in a car. Defensive. I am sure some merchant ships are well manned but bloody sure some aren't too! AIS B is the latest whizz bang. It relies on many assumptions that are not particularly well founded and I too prefer to know where others are and what they are doing well in advance to take appropriate action rather than broadcasting "this is me and I have right of way" In fact I have always thought that was an ideal tombstone inscription. I have fitted an AIS receiver and interfaced with the chartplotter it's a great aid. To tell others where I am, I am considering fitting a Seame whotsit which I would think far more useful than AIS B at this time....
Lets do a side by side comparison then....
Cost - c420 including backup VHF antenna.
Alerts you of other vessels' locations of certain navigation marks. Does not necessarily alert other vessels of your presence, but does convey information should they choose to look you up.
Also tells (smaller) port authorities and rescue services who you are.
Alerts you of other vessel's presence, but not location. Alerts other vessels of your presence and location, but does not impart much information other than perhaps that you are a small craft.
In summary then, there is little to choose in terms of cost. One works well if you want to broadcast your presence and the other works well if you want to broadcast more detailed information as well as receiving similar back.
For me this is a difficult trade off, the waters are quite crowded with commercial stuff but fog is also a regular challenge. Since the greatest hazard with either is being run down by something large that did not see you... and the best way to avoid that is to be aware of them and get out of their way then I think AIS B has the edge.
I for one am not content to sit in my boat sending out a big strong PING safe in the assumption that "they" will go around me. Likewise being in fog and knowing that there is something big out there somewhere is not 100% reassuring.