AIS Question

[Lodesman]

Rule 18 is in section II - conduct of vessels in sight of one another. Section III - conduct of vessels in restricted vis consists of Rule 19 - there is no distinction between vessels that can't see each other.

[bewitched]

Originally Posted by Lodesman

Rule 18 is in section II - conduct of vessels in sight of one another. Section III - conduct of vessels in restricted vis consists of Rule 19 - there is no distinction between vessels that can't see each other.

I think I may have learned something!!.....

.....actually, to be quite honest, I can't get my head round it......

rule 19 applies in bad vis, until you can see each other, then rule 18 kicks in??

[bewitched]

This is the AIS I had on board

http://www.comarsystems.com/csb_200.html

Perhaps I'm being a bit thick here - but why would it transmit my "type of vessel" if this information wasn't to be used for the purposes of navigation?

[Hampus]

I checked it. You can't set navigation status on a class B transponder. You just set the ship type to whatever ship you've got and be done with it The reason for the ship type option is partly for navigational purposes, but mostly for VTS services. The ship type is never changed though.

/Hampus

[Paul Elliott]

There are some significant differences between Class-A and Class-B transponders.

Class-A units transmit quite a bit of Static data, some of which is never changed:Vessel name, callsign, dimensions, etc. Other Static data is supposed to be updated when appropriate: Ship Type and Cargo (combined in a single field), Destination, ETA.

For Class-A, the "Navigation Status" field is contained in the Dynamic position report. This is hand-entered, and often incorrectly.

Class-B units do not transmit any sort of Navigation Status, and there is no data in the Static report that is supposed to be changed. There is the "Shiptype/Cargo" field, but this is definitely not the same as "Navigation Status"

On a practical level, the software provided by the Class-B vendors is obvioulsy not designed for everyday use.

The Class-A "Navigation Status" includes values for "Under Way using Engine", "At Anchor", "Engaged in Fishing", and "Under Way Sailing", among others. I submit that if Class-B users were expected to provide this data, we would have been given a way to do so. Class-B doesn't have a NavStat message, so I think we're off the hook.

So what do we all do in a crossing situation when presented with this ambiguous/incorrect information? I suggest we do what we did before AIS was invented.

[edsailing]

Best bit of navigational kit I have come across is my eyes............. other aids only alert me to what to look out for!

[donradcliffe]

I asked the same question on a different forum as soon as I read the manual on my AIS B transponder. The lack of dynamic status information on sailing vs under power is a definite shortcoming of the Class B AIS, and hopefully may get changed in the future after a few people have been killed and lawsuits filed. All we can do at this time is to use the static definition of a sailing vessel and publicize the shortcomings so that the ships and authorities understand we can't change it.

[rustypirate]

This difference between A and B AIS systems is exactly why I have an AIS A system on my boat.

BTW I don't use mine to keep watch for other boats, but rather to make others around me aware of my presence. The more visible I am to others the better, regardless of how good a lookout I keep.

Remember that the Titanic kept a 24/7 lookout, but that did not prevent them from striking that iceberg.

[btrayfors]

Originally Posted by rustypirate

.....

Remember that the Titanic kept a 24/7 lookout, but that did not prevent them from striking that iceberg.

Yeah, but remember, too, that the Captain was dumb enough to take direction from the ship's owners/managers who wanted to set a record...to the detriment of his own navigational skills, experience, and good judgment.

B.

[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.....!!!

[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.