AIS, Receiver or Transmitter

[El Pinguino]

Originally Posted by MarkJ

What a fool response. I can, you can't so AIS is useless.

Just typical forum b.s..

Ping, you bring great stuff to this forum so I am quite shocked at your attitude on this.

I never said AIS is useless.... I simply say old skills work...nada mas...

[MarkJ]

If you think you can see try counting this white ball

[DotDun]

[QUOTE=Dockhead;2205893]

Originally Posted by chuckr

I think the privacy concern is a serious matter. I don't use Facebook etc. and don't want the whole world to be able to see what I had for breakfast on any given day. I don't like the idea that absolutely anyone, knowing my MMSI or boat name, can see where I am at any given moment, not at all.

But there are all the positive effects you mention. I am sure that I get visited much less by the various coast guards since I am broadcasting AIS and they can easily see not only who we are, but everywhere we've been. Just arrived in the UK after 1500 miles and 8 countries without a single "visit".

I agree, the privacy issues around AIS are atrocious, a complete failure at the architecture layer. It appears the original designers never thought someone would stand up websites and tracking capabilities. But, there are changes that can be made to fix it, IMO needs to do such!

[nigel1]

Just my 2c's worth.
The introduction of AIS had nothing to do with collision avoidance, and with regard to use on most commercial ships, it still has nothing to do with collision avoidance.
However, it has proved highly popular with the small boat users as a means of determining if a risk of collision exists, and that's all we should be using it for in this context, it gives us a warning that a CPA less than that set on the AIS unit could occur, and alerts the user to take heed.
Once you get that warning, then use the eyeball and HBC (or other means to determine what is happening.

[El Pinguino]

Originally Posted by Dockhead

That's my whole point. Here's a scenario:
3. So now you prepare to change course yourself, but you don't know which way to turn, since you can't tell whether he's passing ahead or behind. So you follow correct procedure and alter to starboard.

4. You just changed a 1 mile CPA to a 0 CPA, and you might be 3 or 4 miles from CPA before he notices it.

You've just created a dangerous situation with little time to deal with it, out of a perfectly safe pass -- due to lack of information you could have had from AIS.

This brings us to an interesting issue which transcends AIS and all the fancy stuff.

If a ship alters course to avoid a zero CPA things will improve... as speed remains constant.....

If a yacht alters course to avoid a zero CPA one of two things may happen... its speed may increase or its speed may decrease....
This change in speed combined with the course change can mean that the zero CPA stays a zero CPA.

Hard to explain...

[weavis]

Originally Posted by El Pinguino

This brings us to an interesting issue which transcends AIS and all the fancy stuff.

If a ship alters course to avoid a zero CPA things will improve... as speed remains constant.....

If a yacht alters course to avoid a zero CPA one of two things may happen... its speed may increase or its speed may decrease....
This change in speed combined with the course change can mean that the zero CPA stays a zero CPA.

Hard to explain...

However, On the catamaran the coffee stays stable in its upright position and does not spill regardless.

[El Pinguino]

Originally Posted by nigel1

Just my 2c's worth.
The introduction of AIS had nothing to do with collision avoidance, and with regard to use on most commercial ships, it still has nothing to do with collision avoidance.
However, it has proved highly popular with the small boat users as a means of determining if a risk of collision exists, and that's all we should be using it for in this context, it gives us a warning that a CPA less than that set on the AIS unit could occur, and alerts the user to take heed.
Once you get that warning, then use the eyeball and HBC (or other means to determine what is happening.

Good to see that not too much has changed in the last 11 years ( it seems like just last week... must be an age thing)...

[conachair]

Personally, on the jobs list I would have ensuring the boat has a really good radar return above an ais transceiver.

First things first...

[Dockhead]

Originally Posted by El Pinguino

This brings us to an interesting issue which transcends AIS and all the fancy stuff.

If a ship alters course to avoid a zero CPA things will improve... as speed remains constant.....

If a yacht alters course to avoid a zero CPA one of two things may happen... its speed may increase or its speed may decrease....
This change in speed combined with the course change can mean that the zero CPA stays a zero CPA.

Hard to explain...

Not hard to explain at all!

Except that it doesn't matter who does the course changing -- where a yacht under sail, especially hard on the wind, is involved, it is not possible to determine as precisely where that yacht will be after several miles of sailing. So the CPA has to be big enough to deal with the variations.

[Dockhead]

Originally Posted by nigel1

Just my 2c's worth.
The introduction of AIS had nothing to do with collision avoidance, and with regard to use on most commercial ships, it still has nothing to do with collision avoidance.
However, it has proved highly popular with the small boat users as a means of determining if a risk of collision exists, and that's all we should be using it for in this context, it gives us a warning that a CPA less than that set on the AIS unit could occur, and alerts the user to take heed.
Once you get that warning, then use the eyeball and HBC (or other means to determine what is happening.

I am puzzled why you would not use the information from the AIS, if you have the equipment. You will get a quite precise calculation of CPA, TCPA, and you'll also see his speed and course and very importantly -- his ROT. Updated every few seconds.

HBC is an adequate tool for collision avoidance, but why would you prefer the much poorer data you get from it, updated far less often (maybe once a minute at best?), to the much richer and much fresher data you get from AIS?

Maybe you fundamentally distrust the accuracy of the data from AIS?

Or you just have a pre-AIS workflow, which you prefer not to change?

[MarkJ]

Just as my final point before retiring from this thread...

YOU may be the best seaman in the world and not need AIS or anything else,but what about the other Watch? Can your wife, your crew, Aunt Mabel, do as well as you? Or will you have to be woken up every time a ship/boat/drone appears on the horizon only to pass you 10nms distant?

Even on ships, truly-rooly-biggy ones, can the Captain rely on that underpaid new deck officer doing the Dog Watch? Or does the Captain have to remain awake at all times within 50nms of the coast?

[nigel1]

Originally Posted by Dockhead

I am puzzled why you would not use the information from the AIS, if you have the equipment. You will get a quite precise calculation of CPA, TCPA, and you'll also see his speed and course and very importantly -- his ROT. Updated every few seconds.

HBC is an adequate tool for collision avoidance, but why would you prefer the much poorer data you get from it, updated far less often (maybe once a minute at best?), to the much richer and much fresher data you get from AIS?

Maybe you fundamentally distrust the accuracy of the data from AIS?

Or you just have a pre-AIS workflow, which you prefer not to change?

Dockhead,

I was referring to how I use AIS on a commercial ship.
ARPA, radar and compass bearing are used for ascertaining risk of collision.
We often have AIS overlaid on the ECDIS and on one radar/ARPA, and it is surprising that quite often there is a distinct offset of the AIS target from the radar target. That is enough reason for me not to use AIS as an anti collision tool given the option of the other equipment.

AIS is useful for such information as name, callsign and MMSI, and an indication of CMG and SMG can serve to back up the ARPA data, but given that radar provides a real picture, and AIS is only an input and output of data from various sensors, I'd rather not place too much trust in it.

Now, on the other hand, on a yacht, with a poor performing radar, no ARPA, and a visible horizon of around 3 to 4 miles, I would use the AIS more often as a means to alerting to a developing situation, because it is better than having nothing, but at the end of the day, and I speak only for myself, any action I would take would be based more on compass bearings than the information from the AIS.
I probably still have a distrust in the system having seen how AIS data can be incorrect, or, maybe it's all those years as a watchkeeper and skipper without using AIS.

[nigel1]

Originally Posted by MarkJ

Even on ships, truly-rooly-biggy ones, can the Captain rely on that underpaid new deck officer doing the Dog Watch? Or does the Captain have to remain awake at all times within 50nms of the coast?

Dog watch is OK, they are between 1600 and 2000hrs.
There is a good reason why we put the third mate on the 8 to12 watch, as the skipper is normally up and about during those hours.

[Dockhead]

Originally Posted by nigel1

Dockhead,

I was referring to how I use AIS on a commercial ship.
ARPA, radar and compass bearing are used for ascertaining risk of collision.
We often have AIS overlaid on the ECDIS and on one radar/ARPA, and it is surprising that quite often there is a distinct offset of the AIS target from the radar target. That is enough reason for me not to use AIS as an anti collision tool given the option of the other equipment.

AIS is useful for such information as name, callsign and MMSI, and an indication of CMG and SMG can serve to back up the ARPA data, but given that radar provides a real picture, and AIS is only an input and output of data from various sensors, I'd rather not place too much trust in it.

Now, on the other hand, on a yacht, with a poor performing radar, no ARPA, and a visible horizon of around 3 to 4 miles, I would use the AIS more often as a means to alerting to a developing situation, because it is better than having nothing, but at the end of the day, and I speak only for myself, any action I would take would be based more on compass bearings than the information from the AIS.
I probably still have a distrust in the system having seen how AIS data can be incorrect, or, maybe it's all those years as a watchkeeper and skipper without using AIS.

OK, I see now what you meant.

This is consistent with what many professional mariners have told me -- the procedures developed decades ago and based on radar and ARPA are still primary. On ships.

And I believe that's sensible -- the radar can't lie, and you're not relying on other vessels' having AIS, to avoid them.

We can't work this way on yachts, because our radars are not capable enough. Because of the very small antenna, they don't have the bearing discrimination needed to do proper ARPA (that's my theory anyway).

So for us it's a choice of:

1. Knowing instantly the difference between a collision course, passing a mile ahead, or passing a mile behind, with regard to any target of concern. (AIS)

or

2. Knowing most of that but only after a number of minutes of writing down bearings, requiring concentration and labor, which may be difficult to muster on a short handed yacht and/or may distract you from other important tasks (HBC)

or

3. Knowing almost nothing except that some ship you see is possibly a target of concern (naked eyes; eyes plus stanchion; etc.)


None of this will matter at all if (as we discussed further up in the thread) you're in coastal waters where you know where the ship is going to pass, and can just stay out of the channel or fairway.

It won't matter all that much if you are in uncrowded waters and dealing with only one ship at a time, so that you have time to work the HBC properly, and he has plenty of time to deal with you, if you screw it up.


But it starts to matter a whole lot, and starts to matter very quickly, if you are in heavy traffic and have to deal with multiple targets at once. Even with real time information about CPA, TCPA, how you're crossing, his speed, course, and ROT -- the challenge snowballs with more vessels. Furthermore, you are less and less able to rely on the ship sorting it our for you, because he will ALSO be dealing with multiple targets, and might not get around to you in time.

I just can't imagine why anyone would stick to a collision avoidance work process which does not take advantage of the rich, real time data you get from AIS, on a yacht without the radar you have on your ship. This data makes your work vastly more effective by drastically cutting down the amount guesswork you would otherwise have to do, and by cutting down the false positives and unnecessary (and possibly dangerous) maneuvers, which you may be making because you are unable to discern a safe pass.

[nigel1]

I think we agree here Dockhead, when we discuss the use of AIS on a yacht or other small craft.
AIS is great for filtering out the non-threats, and pointing out those which require our attention.
I would still use compass and eyeball though to confirm what the AIS is telling me, it's not in me to base avoidance action alone on the AIS.
In restricted vis where compass and eyeball are of not much use, well, we fall back on Rule 19, and radar with use of EBL.