VHF/DSC/AIS

[Tintin]

I think there are a lot of people on here that would disagree with you there. AIS receivers allow you to see who is going to hit you when, and take avoiding action. And it works better than RADAR on small vessels because it's not subject to radar's platform stability issues.

AIS transmitting simply puts you on a list of targets that are probably not being tracked actively by the watch on a large proportion of shipping.

I would rather have an active radar reflector than AIS-B transmitting, anyday. And, given the choice of one or the other, I'd rather have AIS receive than RADAR, thanks.

I'm confused (not for the first time, and probably not the last). You seem to be saying that you shouldn't bother with AIS TX because no-one will be watching for it, and yet you then go on to say you would rather have an active radar reflector.

The latter isn't some magic device that wakes up those on watch on ships, so while it may make you appear larger on a radar screen you are still relying on someone looking at that radar screen on a ship to know you are there, which was your argument against AIS tx.

AIS provides a more accurate position to the monitoring equipment and the setting of alarms is simple and straightforward (from what I am told) on ships - simpler than radar proximity alarms because the AIS actually transmits the position rather unlike the radar which has to work it out.

All that said, I would rather have radar over AIS receive any day, because as a previous poster noted, not all vessels have AIS transmit, and modern radar (e.g. Garmin) is very simple to set up and use. I find (now I have got it working!) AIS receive is useful sometimes if I wish to contact a ship that is a bit close for comfort.

At the end of the day I don't think it is a case of either radar OR ais. Both systems complement each other, so having a radar reflector (so someone can see you on their radar) and a radar (so you can see them), and AIS tx/ rx means you get the best of all worlds.

Of course none of this replaces the good old mark one eyeball and the use of binoculars and hand bearing compass, and taking precautions in fog.

Standard Horizon seem to be doing a lot of good product development at the moment at a nice'ish price, and it surely can't be long before someone does a unit for small boats that encompasses VHF / DSC / AIS / CP with wireless link to wind depth and log sensors, all in one unit, at a sub £400 price tag.

chris

 

[AngusMcDoon]

AIS receive-only is a bit like riding a bicycle without lights. OK, it's better than nothing (it just might have saved the Ouzo, for instance, because it would have told them that the Pride of Bilbao was turning) but AIS B is better because then they can see you as well as vice versa.

And for those on limited financial and elelctrical resources, receive only is a lot cheaper and less power hungry, although given time both of these might improve.

 

[supra30]

Horses for courses

I'm confused (not for the first time, and probably not the last). You seem to be saying that you shouldn't bother with AIS TX because no-one will be watching for it, and yet you then go on to say you would rather have an active radar reflector.

The latter isn't some magic device that wakes up those on watch on ships, so while it may make you appear larger on a radar screen you are still relying on someone looking at that radar screen on a ship to know you are there, which was your argument against AIS tx.

AIS provides a more accurate position to the monitoring equipment and the setting of alarms is simple and straightforward (from what I am told) on ships - simpler than radar proximity alarms because the AIS actually transmits the position rather unlike the radar which has to work it out.

My understanding is that a large proportion of commercial shipping does not necessarily have AIS integrated into their ECDIS system... or necessarily use AIS alarms as a part of watchkeeping, so there is no guarantee they will have a nice display, or a loud buzzer sounding to indicate who they are about to run down, even if you are transmitting. I believe at night or in poor visibility, radar is practicially always used by watchkeepers on shipping though.

As for 'stability' and accuracy of alarms, I believe it works the other way around...

With a small vessel with radar/MARPA, the problem is that the radar set is jumping around and consequently establishing good position and position/course/speed data for targets is hard. From the big ship's point of view though, they have a stable platform, and their radar plot of your wildly corkscrewing yacht will just look like a solid position and a slow steady course.

With AIS, it's the other way around. A big vessel cruises merrily on, and you get a lovely solid set of AIS data from it, including rate of turn if it's been properly fitted. The data they get from you though may not be so pretty...

I don't rely upon shipping going around me, though it is of course nice when it does. In reduced visibility or when sailing at night, I am more confident that commercial shipping will be watching radar than looking at some kind of AIS data. An active radar reflector means that I have a radar return that's about the size of a small coaster that will be noticed if there is any kind of watchkeeping using the correct band radar.

Mk I eyeball is king, obviously, but in a situation where you have many vessels converging in close proximity, AIS takes the vast majority of the stress out of the situation as it allows instant appraisal of who is going to pass where.

Last year, crossing from the Channel Islands to the Solent in daylight in good vis, we had a situation crossing the Eastbound shipping lane where we were boxed by 6 vessels... three coming up channel, and three crossing the lane (two northbound, one southbound). AIS told us which vessel was of most concern immediately, and allowed us to hold course until the other conflicts had cleared, and we could shape to pass around his stern. That was a difficult enough situation with AIS there to provide instant data. I would not have liked to be in that position relying upon Mk I eyeball and a handbearing compass.

Regards,

Mike