2018 Rolex Sydney Hobart Yacht Race: The Race Committee has lodged a protest against Wild Oats XI

[axolotl]

That is just getting confused.

There are two sets of satellites being talked about. The GPS/Glonass/Galileo ats that transmit the positioning information. All AIS systems use at least one of these sat sets. The various commercial sats carrying specialised AIS receivers that provide data feeds to commercial subscription services. 

CSTDMA Class-B transceivers are limited to 2 watts. Generally too low power to be received by any of the satellites carrying AIS receivers. SOTDMA class B and of course class A have higher power (5 and 12 watts respectively) and can be received. Generally it seems the fleet is still using CSTDMA class B. Even if someone did subscribe to one of the services offered by the sat owners with AIS receivers, you would not usually see the fleet.

I'd disagree. STDMA does not transmit to S-AIS and Class-B transmissions to satellites even with SOTDMA are not generally supported.  Get it in your skull that AIS on pleasure boats is local, 10 miles or so, satellites are not involved.

 

[Crazy Cat]

I guess we will never know for sure but as Tricky said, apart from this issue they sailed the pants off the old girl.

No they didn’t. They sailed an average race and got lucky that they were NOT in the lead on approach to Tasman Is. Comanche showed the other three that the transition was further off the coast than expected and they could all avoid it. Don’t forget that The Indian made WOXI look pretty stupid when she glided past around 0300 on Thursday in light winds to overtake them for the second time. 

I maintain that the AIS had nothing to do with the result. But I have never said that a breach of the rules is ok, as some here have made out. Totally agree that a proper sportsman would RAF. 

 

[Rail Meat]

Dunce.  AIS-B is not satellite based and does not require a subscription.  Perhaps you're confusing AIS with satellite tracker systems like YellowBrick, Spot, Explorer+, etc.  Go over and stand in the corner for 60 minutes.

I am not confusing anything. On the other hand, your reading comprehension is pretty limited. So fuck off.

I am perfectly aware that AIS-B is not satellite based and does not require a subscription.   What I was referring to was the ability to research if other boats had been transmitting, given that a good portion of the race was done out of range of land based receiving stations.  Thus the need to look for services that track AIS data from both land receiving stations and satellite.  

And yes, to Francis' point CSTDMA Class B units transmit on lower power but I have actually seen a lot of signals from what I believe to be CSTDMA equipped boats get picked up by the satellite receivers.  Or maybe they are actually SOTDMA equipped and I guessed wrong.  I upgraded to SOTDMA this past year.

 

[axolotl]

If you are a few nm away from an opponent, and he decides to head offshore at night to follow a wind shift, his AIS B position will tip you off..

Eggzactly.  Radar, SAT trackers, visual observation will always be less accurate than an actual ping on the AIS-B network.

 

[Rail Meat]

I'd disagree. SOTDMA does not transmit to S-AIS and Class-B transmissions to satellites even with SOTDMA are not generally supported.  Get it in your skull that AIS on pleasure boats is local, 10 miles or so, satellites are not involved.

Still stupid.

Yes, your Class B signal will get picked up by Sat receivers even when they are not being picked up by land stations.  Which is exactly how Just a Skosh was able to show us the screen shots of Commanche and Black Jack transmitting all the way through the race, and WOXI failing to transmit.  So again, fuck off.  

 

[Crazy Cat]

Yes, and I bet they think it now was not worth it.

There is no excuse for being such a cunt that you break the most fundamental rule in the sport.

No way MR regrets it. Last year when his afterguard advised him to do the turns he (allegedly) said “no fuck it we nailed him”.  And what is there to regret? Bunch of us moaning online about him but he doesn’t read this thread and wouldn’t care if he did.  Maybe Sandy does (regret it) but he doesn’t understand enough about the whole picture, he just sees a lot of people saying not nice things about his boat that just won and is puzzled. 

 

[Francis Vaughan]

I'd disagree. SOTDMA does not transmit to S-AIS and Class-B transmissions to satellites even with SOTDMA are not generally supported.  Get it in your skull that AIS on pleasure boats is local, 10 miles or so, satellites are not involved.

Sorry, I think you have misunderstood my point.

The commercial sats are passive, they are not any sort of official part of AIS operations. They are a fortuitous capability that was not designed into AIS, and took a lot of serious effort to get working (because they have such a wide field of view the sats see overlapping transmissions in the same slots, and must untangle them). If the sats can hear the AIS transmitter they will decode the transmissions and relay it to their commercial subscription services - unless they explicitly filter class B out. This capability is independent of class. There is nothing that the AIS transmitter has to do with the service to be heard, except to be loud enough.

The entire point of SOTDMA versus CSTDMA for S-AIS is the power level. 2 watts isn't generally enough to get heard. So yes, for pleasure boats S-AIS isn't an issue. You won't be reliably seen, if at all. If you install a SOTDMA class B unit there is every chance you will be seen by S-AIS. The ubiquity and cheapness of SOTDMA class B units is going see a lot more pleasure boats appearing in S-AIS as time goes on. There is no intrinsic difference between SOTDMA class B and class A except for power levels and the amount of information provided about the vessel, and use of additional information capabilities available in class A. CSTDMA class B is basically the same as SOTDMA class B, but does not participate in slot reservation, and is restricted in power because of this.

 

[Rail Meat]

Sorry, I think you have misunderstood my point.

The commercial sats are passive, they are not any sort of official part of AIS operations. They are a fortuitous capability that was not designed into AIS, and took a lot of serious effort to get working (because they have such a wide field of view the sats see overlapping transmissions in the same slots, and must untangle them). If the sats can hear the AIS transmitter they will decode the transmissions and relay it to their commercial subscription services - unless they explicitly filter class B out. This capability is independent of class. There is nothing that the AIS transmitter has to do with the service to be heard, except to be loud enough.

The entire point of SOTDMA versus CSTDMA for S-AIS is the power level. 2 watts isn't generally enough to get heard. So yes, for pleasure boats S-AIS isn't an issue. You won't be reliably seen, if at all. If you install a SOTDMA class B unit there is every chance you will be seen by S-AIS. The ubiquity and cheapness of SOTDMA class B units is going see a lot more pleasure boats appearing in S-AIS as time goes on. There is no intrinsic difference between SOTDMA class B and class A except for power levels and the amount of information provided about the vessel. CSTDMA class B is basically the same as SOTDMA class B, but does not participate in slot reservation, and is restricted in power because of this.

Thanks. You were more polite than I was, and more erudite.

 

[savoir]

Dunce.  AIS-B is not satellite based and does not require a subscription.  Perhaps you're confusing AIS with satellite tracker systems like YellowBrick, Spot, Explorer+, etc.  Go over and stand in the corner for 60 minutes.

Actually it is you that is the dunce. EVERY class B AIS is satellite based. Nothing else is possible.

This may come as a bit of a shock to one with your level of arrogance but the VHF antenna that is integral to every AIS system also transmits UP as well as out. Amaaaaaazing. The signal going up has a range of hundreds of miles.  There are a whole lot of satellites up in the sky ( round about 50 ) that relay these transmissions to a base station.

While I'm here, in another post you also told everyone that AIS class B units come with an on/off switch for the transmit function. THEY DO NOT. Each of the Garmin, Furuno, Simrad and B & G units comes from the dealer without such a switch. A switch can be fitted but that is an after purchase decision for each boat owner to make. One would assume that anyone fitting this type of switch intends to use it.

How about you wander over to the dunce's corner, tell Rail Meat all is forgiven and give him a big hug. There's a good boy.

 

[axolotl]

Sorry, I think you have misunderstood my point.

The commercial sats are passive, they are not any sort of official part of AIS operations. They are a fortuitous capability that was not designed into AIS, and took a lot of serious effort to get working (because they have such a wide field of view the sats see overlapping transmissions in the same slots, and must untangle them). If the sats can hear the AIS transmitter they will decode the transmissions and relay it to their commercial subscription services - unless they explicitly filter class B out. This capability is independent of class. There is nothing that the AIS transmitter has to do with the service to be heard, except to be loud enough.

The entire point of SOTDMA versus CSTDMA for S-AIS is the power level. 2 watts isn't generally enough to get heard. So yes, for pleasure boats S-AIS isn't an issue. You won't be reliably seen, if at all. If you install a SOTDMA class B unit there is every chance you will be seen by S-AIS. The ubiquity and cheapness of SOTDMA class B units is going see a lot more pleasure boats appearing in S-AIS as time goes on. There is no intrinsic difference between SOTDMA class B and class A except for power levels and the amount of information provided about the vessel. CSTDMA class B is basically the same as SOTDMA class B, but does not participate in slot reservation, and is restricted in power because of this.

Well said.  The point is a Class-B STDMA devices, which I suspect were the devices used on all the S2H boats, are not generally reported by satellite reception due to weak transmission power;  they're  designed for boat to boat close in encounters.

That being said, many commercial entities have deployed S-AIS systems which are entirely reliable assuming a SOTDMA transmitter, have resolved the problem of the satellite's big footprint concerning reception (thousands of transmitters) and are a go to technology for commercial traffic. So the present state of advanced AIS is robust, not so much for a racing sailboat with a 3 year old AIS system.

 

[Maw]

Dumb question if I may:

How do I determine if my Class B transponder is CSTDMA or SOTDMA?

The only tech reference I can find to the satellite side is its a 50 channel IEC 61108-1 compliant device? 

Edit: I can see SOTDMA is referenced to the IEC standard, but no CSDTMA? 

 

[Maw]

Ok, reading up on it I could determine which unit I have is based on improved output power and TX time which has improved a lot to 5W and 5 sec from 2W and 30 sec. That confirms my previous question about uplinking to sat.

It's interesting my user manual, or tech specifications doesn't tell me:

- any reference to sat TX uplink, only VHF TX. No mention of output power, freq or modulation type at all.

- whether it is SOTDMA or CSDTMA. No output power of rate to reference to at all.

Interesting thread drift.

 

[Trickypig]

No they didn’t. They sailed an average race and got lucky that they were NOT in the lead on approach to Tasman Is. Comanche showed the other three that the transition was further off the coast than expected and they could all avoid it. Don’t forget that The Indian made WOXI look pretty stupid when she glided past around 0300 on Thursday in light winds to overtake them for the second time. 

I maintain that the AIS had nothing to do with the result. But I have never said that a breach of the rules is ok, as some here have made out. Totally agree that a proper sportsman would RAF. 

I’m amazed you think AIS could have not been a tactical advantage. If you’ve ever done any one design offshore races you would have spent a lot of time conjecturing whether a competitor has better/worse breeze or current. You would have been keeping an eye on their bearing swith a compass, putting the binoculars on them to look at the pressure in their kite etc etc etc.

Imagine if you have their accurate boatspeed and heading on a screen but they don’t have yours? 

You said WOXI sailed an ‘average ‘ race despite them winning. Does that mean the other boats were below average?

 

[Francis Vaughan]

How do I determine if my Class B transponder is CSTDMA or SOTDMA?

If it is much older than a year it will almost certainly be CSTDMA. SOTDMA class B is the new thing, you would know when you bought it. Otherwise just check the manufacturer's web site. Generally, I'd say if you didn't already know it was SOTDMA it is CSTDMA.

 

[weightless]

VHF antenna that is integral to every AIS system also transmits UP as well as out.

I'm not sure "satellite based" means what you think it means.

Also most VHF antennas are less good at UP [sic] than out,

And polarization might be tricky.

It's kinda amazing to me that it works at all satisfactorily with the sats.

 

[Maw]

If it is much older than a year it will almost certainly be CSTDMA. SOTDMA class B is the new thing, you would know when you bought it. Otherwise just check the manufacturer's web site. Generally, I'd say if you didn't already know it was SOTDMA it is CSTDMA.

 Unit is 3 years old, so thanks Francis, that makes sense.

 

[Maw]

I'm not sure "satellite based" means what you think it means.

Also most VHF antennas are less good at UP [sic] than out,

And polarization might be tricky.

It's kinda amazing to me that it works at all satisfactorily with the sats.

Thanks weightless,

I just twigged to the AIS Satellite frequency is the VHF band, so it's using the VHF Transmitter to do both local VHF and as the satellite uplink. . 

Now I get it.

Thanks!

Edit: Interesting sidenote: my installation instructions says not to use an antenna at the top of the mast for satellite rx due to the motion. So that's why my rx gps antenna is separate and at waterline level. 

 

[Cal20sailor]

I'm not sure "satellite based" means what you think it means.

Also most VHF antennas are less good at UP [sic] than out,

And polarization might be tricky.

It's kinda amazing to me that it works at all satisfactorily with the sats.

You are so full of shit.  

 

[Francis Vaughan]

And polarization might be tricky.

It's kinda amazing to me that it works at all satisfactorily with the sats.

Well you drew an ideal dipole response, the little loaded whips they put on the masts are not quite so directional, but you are dead right. The sats are sucking on the aether pretty hard to get the signals. There is some seriously fine engineering going on. (I did read about how they handled polarization a while back, but have forgotten what they did. It might even be possible it can be used to help untangle the slot overlaps.)

 

[weightless]

I'm not sure "satellite based" means what you think it means.

Also most VHF antennas are less good at UP [sic] than out,

And polarization might be tricky.

It's kinda amazing to me that it works at all satisfactorily with the sats.

You are so full of shit.  

Bummer. I thought that was all correct. What'd I fuck up?