AIS permanently on, do you?

[Minerva]

AIS is one of those annoying things I don't miss.
Even so.
AIS if you get it set up can actually be quite useful.
The best thing about AIS if you have a transponder. AIS is quite helpful if you are underway. Particularly when the weather is crap.
In my opinion a Gentleman. Changes her AIS status. When she is not underway.
The rest of us appreciate the consideration.
If you RTFM a little bit off swearing and buggering about with the menu. You can turn of CPA and TCPA alarms for moored vessel's.
So you don't get to many.
Unfortunately most marina's seam to be full of inconsiderate wankers who can't be bothered to change their AIS vessel status from underway to moored or turn it off.
If you have ever heard of "pre departure checks" or "post arrival checks", Add update, AIS status.
Particularly if you happen to have your AIS hooked up to one of those annoying GMDSS radios.
The Red button includes such useful info as No of people on Board. Which might come in handy. If it's up to date. Could be very annoying if its not.
Not sure if class B can or can't display no of people on board.
If you don't know how to change AIS status. RTFM.
Or turn it off.
Unless the AIS is part off an all integrated system. Which will set off all kinds of alarms in the rest of the integrated system. So no, I usually changed the status and left the AIS on. Except for a longer duration when we were going to shut down the entire system.

On a class b, recreational vessel? Did you aye?

 

[lustyd]

A “wake up” alarm can indeed be a useful prompt.

I set an alarm on my phone for 20 mins when on watch. I reset it at about 13-15 minutes when I look around. Bigger passages also get radar and AIS alarms. I’m more than willing to accept some help from tools and happy to accept humans aren’t as good as we think we are

 

[SaltyC]

I know

But the salty dude suggested mine also isn’t compliant for some reason? AFAIK it is.

And I’d guess the other guys is compliant, he just doesn’t realise that it has its own built in GPS.

Mine does not have its own GPS, fed from plotter on same 12v feed.

 

[noelex]

AIS alarms vary significantly between different units. Some are very poor, and the only option is to turn them off to prevent the false positive responses in some situations. Others are smarter and more adjustable.

 

[Phil_boat]

Mine does not have its own GPS, fed from plotter on same 12v feed.

I’m surprised, I didn’t think that was a thing.

Or is yours only a receiver?

 

[SaltyC]

I’m surprised, I didn’t think that was a thing.

Or is yours only a receiver?

It's a transiever, my post was badly worded and probably mis understood.
The AIS is on the same 12v breaker as the chart plotter from which it recieves a GPS Signal and transmits to for display of targets.
In this way it turns on as soon as the plotter is powered and I on't have to remember to turn on.
In tge process of fitting new electronics and will once again wire the power in parallel with the plotter. Just need to get laptop and instruction book out to change output fo NMEA 2000.

 

[st599]

It's a transiever, my post was badly worded and probably mis understood.
The AIS is on the same 12v breaker as the chart plotter from which it recieves a GPS Signal and transmits to for display of targets.
In this way it turns on as soon as the plotter is powered and I on't have to remember to turn on.
In tge process of fitting new electronics and will once again wire the power in parallel with the plotter. Just need to get laptop and instruction book out to change output fo NMEA 2000.

It has to use it's internal GPS if it's a class B. Are you sure that it's not multiplexing two GLL sentences?

 

[SaltyC]

It has to use it's internal GPS if it's a class B. Are you sure that it's not multiplexing two GLL sentences?

Hmmm, me and electronics are not happy bedfellows. Need to talk to Digital Yacht.

 

[dunedin]

It has to use it's internal GPS if it's a class B. Are you sure that it's not multiplexing two GLL sentences?

Doesn’t need to be an “internal GPS” - our Raymarine AIS uses a separate external but directly connected GPS antenna.
The other GPS antenna used for the plotters, is connect into SeaTalkNG (NMEA 2000)

 

[Sjp1960]

I understand that all AIS transmitters have to be synchronised down to the ms level as AIS is based on timed slots. The only practical way to achieve this is to have a built in GPS which has access to the atomic clock data signals from the GPS satellites. N2K data from a chartplotter would be fine for positioning but doesn’t provide adequate timing data. The AIS can use an internal or external antenna for the GPS.

 

[lustyd]

That’s not how timed slots work, they use internal clock to transmit regularly and a collision detection algorithm to randomly change slot if a collision is detected. It doesn’t require the actual time.

 

[Sjp1960]

That’s not how timed slots work, they use internal clock to transmit regularly and a collision detection algorithm to randomly change slot if a collision is detected. It doesn’t require the actual time.

 

[Sjp1960]

You are mistaken. Class A and class B+ use SOTDMA. The patent is here

https://worldwide.espacenet.com/patent/search/family/027355635/publication/US5506587A?q=pn=US5506587

and explains how the precise GPS time base is used to define the slots. There are 2250 slots and the 1st slot starts on the minute boundary down to the millisecond. The concept of the patent was to avoid the need for a central base station defining the slots by using the GPS clock.

Class B uses a form of collision detection to identify unused slots but it still needs a precisely synced clock to identify the slots.

You might suggest that a class B transmitter could work without a precisely synched clock as it could identify the slot timing by listening to other transmitters. However this breaks down if there are no class A transmitters in range and you would get groups of class B vessels using different slot timing to other groups of class B vessels that then encounter each other how would two such groups agree on the right slot timing?

 

[st599]

That’s not how timed slots work, they use internal clock to transmit regularly and a collision detection algorithm to randomly change slot if a collision is detected. It doesn’t require the actual time.

Both Class B and Class A/B+ use timed slots, which requires very accurate timing to establish when slot 0 starts and to lock the clock within the AIS.

 

[st599]

You might suggest that a class B transmitter could work without a precisely synched clock as it could identify the slot timing by listening to other transmitters. However this breaks down if there are no class A transmitters in range and you would get groups of class B vessels using different slot timing to other groups of class B vessels that then encounter each other how would two such groups agree on the right slot timing?

It also assumes a zero propogation delay which isn't feasible.