AIS Question

[btrayfors]

Lodesman,

Yes, there is. And it makes perfect sense for vessels in close proximity to one another.

However, if you're an alert helmsman you do it LONG BEFORE you're in a close situation. Why? Because a very slight course change on your part can avoid any chance of a collision, without inconveniencing either you or the "burdened" vessel....which in my home waters might well be a huge commercial or war ship.

Bill

[Lodesman]

Originally Posted by btrayfors

However, if you're an alert helmsman you do it LONG BEFORE you're in a close situation. Why? Because a very slight course change on your part can avoid any chance of a collision, without inconveniencing either you or the "burdened" vessel....which in my home waters might well be a huge commercial or war ship.

And if the "alert helmsman" in the give-way vessel decides to make a slight course change to starboard...

[btrayfors]

Unlikely. Don't forget, we're talking about crossing situations and the vessels are WAY FAR APART. Also, the give-way vessel is very likely to be much faster than the sailboat, so in order to pose a threat he'd have to make a substantial course change, not a slight one.

The idea is to nip a dangerous situation in the bud....long before there's any real danger. And, very often, this can be done in a relatively slow-moving sailing vessel by just a slight course change. And, of course, by careful monitoring of the situation by all reasonable means available.

So long as the relative bearing to the give-way vessel is changing -- in this case moving ahead toward the bow -- and he's still a long way off, you're golden.

What's a "long-way"? Obviously, this depends on the situation...weather conditions, sea condition, speed of each vessel, angle on the bow, etc.

As the wise old San Francisco Bay pilot said, "There's only one Rule of the Road you have to respect, and that's give way to tonnage" :-)

Bill

[bewitched]

Originally Posted by rustypirate

BTW I don't use mine to keep watch for other boats, but rather to make others around me aware of my presence. .

This is the primary function in my view. Second is the ability to call the other ship by name / callsign.

I've had to transit Singapore twice at night - once with AIS Transponder, once without. without was terrifying, with it was so much easier

They can see me.....!!!

[Lodesman]

Originally Posted by btrayfors

Also, the give-way vessel is very likely to be much faster than the sailboat, so in order to pose a threat he'd have to make a substantial course change, not a slight one.

???

[barnakiel]

Never seen a B unit with switch over functionality. All I have seen was set-and-forget!

How do they do it on tall / training / sailin ships? Do they switch over when motoring?

Most interesting!

???
b.

[s/v Jedi]

We still have our class A and we change between "moored", "anchored" and "underway".

cheers,
Nick.

[billyehh]

I don't have AIS and rarely use my radar. However I have my handy dandy bearing compass that will tell me fairly quickly if I am on a collision course. I don't care who is in the right of way and change course making my intensions clear.

In a recent Practical Sailor they stated that class A units can turn off class B signals and many ships do to reduce clutter on their screen. So do not take for granted that you can be seen by that ship unless you have a class A unit.

[rebel heart]

Originally Posted by billyehh

I don't have AIS and rarely use my radar. However I have my handy dandy bearing compass that will tell me fairly quickly if I am on a collision course. I don't care who is in the right of way and change course making my intensions clear.

In a recent Practical Sailor they stated that class A units can turn off class B signals and many ships do to reduce clutter on their screen. So do not take for granted that you can be seen by that ship unless you have a class A unit.

A lot of boat owners these days would rather just plug in gizmos to take care of problems than learn about constant-bearing-decreasing-range.

I've said it before and I'll say it again: not a lot of maritime screw ups happening by crews who know proper seamanship, navigation, and piloting.

[Paul Elliott]

Originally Posted by billyehh

In a recent Practical Sailor they stated that class A units can turn off class B signals and many ships do to reduce clutter on their screen. So do not take for granted that you can be seen by that ship unless you have a class A unit.

Ships do not disable reception of Class-B signals!

This is a myth that has been propagating since the introduction of Class-B, but it is not true! What is true is that some early AIS receivers/transponders/systems could not completely decode Class-B signals, since the format for some of them went through changes while the specifications were being worked out. Even then, the most important data (position, course, speed) has always been decoded properly. The Class-B vessel name and other static information may not be decoded with this early gear.

There are also a few "hobby-level" AIS programs that let the user select what types of transmissions will be shown. Nothing that is likely to be used on the bridge of a Class-A equipped ship will provide this capability.

There have been concerns that Class-B transmissions will clutter the AIS screens, but so far at least this hasn't been a big problem. As these systems evolve there may be some fancy filtering available, but "Ignore Class-B" isn't going to be one of these.

That said, you should never assume that your AIS signal (A or B) will be seen on the bridge of a ship. The legal-minimum display unit is just a screen with a few lines of text, and the crew might be busy looking elsewhere. Your safety is in your hands, not theirs.

[Hampus]

Originally Posted by Paul Elliott

Ships do not disable reception of Class-B signals!

All you wrote is true. There are some VTS systems that allow filtering of class B transponders though. They actually allow filtering of class A transponders too, but the operator would be more inclined to filter class B...

/Hampus

[fishwife]

Imagine "300,000 Ton Ship Runs Down 15 ton Yacht, Ships AIS Tuned To Ignore Recreational Vessels". And the at the subsequent inquiry the Captain being asked to account for that. It can't be done, and I just can't see anyone fitting (illegal) software on a merchant ship that would allow it.

Paige

[osirissail]

btrayfors - - Just a question - >> which in my home waters might well be a huge commercial or war ship.<<< Have you had a chance to observe "war ships" on your AIS? It was my understanding that they do not broadcast AIS information for naval security reasons. It would be interesting if anybody with AIS has ever seen AIS targets coming from Naval Warships and whether they were entering harbors or out at sea?

[s/v Jedi]

Warships have their own AIS vessel-type so I think they will enable transmit when they feel that security isn't an issue... meaning they which will never transmit at sea.

cheers,
Nick.

[btrayfors]

Originally Posted by osirissail

btrayfors - - Just a question - >> which in my home waters might well be a huge commercial or war ship.<<< Have you had a chance to observe "war ships" on your AIS? It was my understanding that they do not broadcast AIS information for naval security reasons. It would be interesting if anybody with AIS has ever seen AIS targets coming from Naval Warships and whether they were entering harbors or out at sea?

No, I haven't seen one on my AIS. I don't have or want AIS aboard my vessel. I know this is swimming upstream against the current AIS frenzy, but as an old navigator I believe it's:

1. unnecessary;
2. another complication;
3. not synoptic and thus potentially very misleading;
4. downright dangerous as many inexperienced sailors will be lulled into a false sense of security and/or waste valuable time looking at displays and data which are largely irrelevant.

That's the whole point: warships are very unlikely to show up on your AIS display. So, too are:

1. almost all yachts and small recreational vessels;
2. almost all fishing boats;
3. buoys;
4. fishing nets, pots, etc.
5. barges;
6. flotsam (logs, trees, containers, etc.)

Most of these WILL show up on radar, though, and virtually all of them will show up on your Mark I eyeballs, providing you are keeping a sharp watch and, at night, haven't spoiled your night vision staring at mostly irrelevant screen data.

Yeah, I concede it's nice to know a ship's name if you want to hail them on VHF. However, I've not had much of a problem contacting other vessels -- mostly on the Channel 13 bridge-to-bridge channel -- even without knowing their names. Further, it's rarely necessary to make contact anyway. If you think there's some risk of collision -- even the faintest one -- STAY OUT OF THEIR WAY. Don't waste time trying to contact them.

JMO, as always.

Bill