What does your Class B AIS transponder do for you?

[donradcliffe]

Here are a couple of forms for the data legally required to be input by the Seller.

https://www.milltechmarine.com/Vesse...m_ep_58-1.html

https://www.westmarine.com/ais-registration.html

[wholybee]

Originally Posted by Flatswing

Yes -good point. My understanding was transmission of additional info. like boat name etc. was every 2 minutes. Perhaps it's longer? I typically have the AIS targets on screen for 10+ minutes since I cruise at 7.5Kn or less. Perhaps RSLifkin is correct in that the dealers are inputting the MMSI, perhaps expecting the boat owner to add the boat name & other details later? Hailing another boat by its MMSI is pointless, I certainly don't have mine memorized.

I'm am 90% sure it is every 6 minutes. And sometimes class B AIS packets will get lost due to a collision unless they are SOTDMA, so if that only every 6 minutes packet is lost, then it becomes 12.

A dealer might choose to enter only the MMSI, but I think it would be negligent. When I bought mine everything was programmed for me, even down to the dealer asking me offset of the GPS antenna from the center of the boat.

[Flatswing]

Originally Posted by Flatswing

Well the quoted reply sounds very authoritative. Unfortunately, it’s incorrect.
I bought my Vesper XB8000 here in the US from a respected marine electronics dealer. The instructions to set it up with boat name, MMSI etc. are easy to follow and were done after the (self) install to add the antenna placement parameters etc.

I should correct my previous erroneous statement: I went back & checked my records of my AIS self install. As others stated (correctly) I was required to provide to the dealer my MMSI number, call sign & boat length. I added the boat name & modified some of the boat parameters via my laptop post installation. So my apologies for relying on memory and providing initially incorrect info.

Hopefully this also explains my original concerns that many boats don’t publish their boat names on AIS - making hailing difficult.

[Hartleyg]

Those with an interest in the actual rules and technical aspects of AIS should check out the USCG pages at https://www.navcen.uscg.gov/automati...ystem-overview


FWIW, both Class A (Big ships) and Class B (us "little guys") are required to transmit our information packets (name, dimensions and status) every 6 minutes, while position, course & speed are more often, depending on vessel speed.


Regarding who is supposed to program the info, the USCG says that the "installer, manufacturer or retailer" is responsible for programming Class B, and that the "User" cannot do so. So if you buy an AIS and install it yourself, you are the "installer" and responsible for proper programming


Hartley
S/V Atsa

[Nicholson58]

We have an old Watchmate 850. It has saved our skins several times on night transits in the Caribbean. One was a tug and tow behind on 1500 meter cable. The barge light was too far, low and dim to see. After a short conversation with the tug pilot he suggested to turn five and slow by 3/4 so we would pass ahead. Behind would have been death.

The 850 also performs as a very low power anchor watch while continuing to broadcast our position.

[sv_pelagia]

Originally Posted by Nicholson58

We have an old Watchmate 850. It has saved our skins several times on night transits in the Caribbean.

The 850 also performs as a very low power anchor watch while continuing to broadcast our position.

We love our Watchmate 850. And yes, the anchor watch/alarm is a great feature. At the risk of restarting the AIS off/on at anchor debate, the 850 anchor watch works also while not transmitting.

[IanSchlueter]

One of the best additions to my boats safety tools. I have had cargo ahios contact me by name before I could see them who wanted to know my intentions. On ocean passages I have seen ships divert well over the horizon as our CPA narrowed. AiS both send and receive are extremely effective and useful to have. I personally would like to see transponders mandated on more watercraft. Knowledge is power.

[Talbot]

Is it good for you - only in certain circumstances and provided you understand the limitations of Class B.
In a crowded coastal environment, such as the Solent/English Channel, The number of transponders in Class A swamp the frequency and few Class B are let through before the Class A starts again for its next transmission. You are therefore left in the dark whether that big merchie has seen you on their AIS.
Personally I prefer using a pure AIS receiver only. I can adjust my course such that the merchie thundering down the channel does not have the need to worry their watch dog about a possible course alteration.

[wholybee]

It really depends on where you are and the type of sailing you do. Someone could also make an argument that flares are a waste of money, or an EPIRB, or liferaft. But I think there is near consensus that for a boat going offshore not having those things is negligent.

There are plenty of near shore sailing areas where AIS isn't particularly important - until it is. We are not there yet, but we are moving toward AIS transmitters being standard equipment, and not having it being negligent.

[Nicholson58]

Originally Posted by Talbot

Is it good for you - only in certain circumstances and provided you understand the limitations of Class B.
In a crowded coastal environment, such as the Solent/English Channel, The number of transponders in Class A swamp the frequency and few Class B are let through before the Class A starts again for its next transmission. You are therefore left in the dark whether that big merchie has seen you on their AIS.
Personally I prefer using a pure AIS receiver only. I can adjust my course such that the merchie thundering down the channel does not have the need to worry their watch dog about a possible course alteration.

That big boat, class A has a priority system. If you are close he will see you. Our Watchmate 850 shows everything unless you set the filters.

[rslifkin]

Class B+ (SOTDMA) transceivers avoid the transmit congestion issue. They use the same transmission slot algorithm as class A, just at lower power and with a few other differences. Regular class B only transmits when it finds a quiet spot to do so, so they can have issues with not being able to transmit frequently in really busy areas.

[wholybee]

Originally Posted by Talbot

Is it good for you - only in certain circumstances and provided you understand the limitations of Class B.
In a crowded coastal environment, such as the Solent/English Channel, The number of transponders in Class A swamp the frequency and few Class B are let through before the Class A starts again for its next transmission. You are therefore left in the dark whether that big merchie has seen you on their AIS.
Personally I prefer using a pure AIS receiver only. I can adjust my course such that the merchie thundering down the channel does not have the need to worry their watch dog about a possible course alteration.

The most crowded spot I have ever been was transiting the Panama canal, with IIRC about 300 other ships transmitting AIS. I did not have this problem there. So, if that issue does exist, it is going to be really rare. Yes, in theory it can, but in practice, I don't think it is a real issue.

[Statistical]

Originally Posted by rslifkin

Class B+ (SOTDMA) transceivers avoid the transmit congestion issue. They use the same transmission slot algorithm as class A, just at lower power and with a few other differences. Regular class B only transmits when it finds a quiet spot to do so, so they can have issues with not being able to transmit frequently in really busy areas.

Yeah and price between Class B & B+ (SOTDMA) is really narrowing. Some vendors like Garmin only have SOTDMA option. Honestly there really is no reason for them to be materially more expensive and a single unit gets better economies of scale. I could see "normal" Class B (CDTDMA) getting phased out by vendors.

If congestion does become an issue AIS should be improved to add additional channel(s). This was already done once with AIS3 & AIS4 although those are only used for sat reception.