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Old 23-09-2019, 18:56   #16
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Re: Advantage of Class B+ AIS on a sailboat?

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But do you get seen by others at that sort of range?
Stu

I doubt if he's seen at 30 something miles. WE have our AIS set for showing anything less than 18 miles out. I've called various ships and they have confirmed that they usually see us at about 20 miles (depending on weather conditions).

Ours is a 5 year old class B - works very well with an antenna splitter.

And I agree with Dockhead - big ships make their decisions and course changes far earlier than the rest of us. We have adopted their safety margins - if we're going to get closer than 1 nm to a ship we give way (if we are the give way vessel) or call them and discuss it - so far, in 3 1/2 years of constant sailing - every ship we have called has answered and we reached agreement on our intentions without any issues
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Old 24-09-2019, 00:12   #17
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Re: Advantage of Class B+ AIS on a sailboat?

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Stu

I doubt if he's seen at 30 something miles. WE have our AIS set for showing anything less than 18 miles out. I've called various ships and they have confirmed that they usually see us at about 20 miles (depending on weather conditions).

Ours is a 5 year old class B - works very well with an antenna splitter.
I don't know how tall your mast is, but 20NM shouldn't be far from the combined radio horizons. Quite an impressive value especially trough a splitter and a channel 16 optimized antenna. Seems I don't need to look any further than the good old Class B...
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Old 24-09-2019, 01:09   #18
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Re: Advantage of Class B+ AIS on a sailboat?

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I see absolutely no point of getting a Class A system for a moderate size sailing boat. If you feel the need of any advantage over Class B, B+/SOTDMA will get you there:
- enough power to be picked up by satellites(!) <-however, this is not hopeless with simple class B either.
- more frequent transmissions
- <half price compared to Class A (still more than Class B).
A class A system has the ability to pass details of what the ship is actually doing. e.g. not under command, fishing etc...
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Old 24-09-2019, 01:11   #19
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Re: Advantage of Class B+ AIS on a sailboat?

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I see absolutely no point of getting a Class A system for a moderate size sailing boat. If you feel the need of any advantage over Class B, B+/SOTDMA will get you there:
- enough power to be picked up by satellites(!) <-however, this is not hopeless with simple class B either.
- more frequent transmissions
- <half price compared to Class A (still more than Class B).

I agree and think that Class A makes no sense for 99% of recreational sailors.


B+ does just about everything any of us could wish for.


I looked into Class A before B+ was released and decided not to do it, because it is a lot more work to operate Class A -- you have to enter and change nav status every time sails come up or down.


B+ is perfect for us.
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Old 24-09-2019, 05:13   #20
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Re: Advantage of Class B+ AIS on a sailboat?

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OK, Sailors, I'm in the process of a refit for my newly acquired Tartan 37 for east coast and Island sailing. I have a blank canvas, what AIS do I install? Class A or B system?

Do you all have AIS at the helm or only at the Nav station?

Ours is B. If I were indstalling to day, I'd put in B+. No need for A.

At the helm... where one would normally make steering decisions relevant to other vessel traffic. If the "nav station" is buried below decks, an AIS display there wouldn't be immediately useful.

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Old 24-09-2019, 10:16   #21
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Re: Advantage of Class B+ AIS on a sailboat?

Not under command and/or fishing are clearly easy to see on Class B... not under command, speed zero, fishing commercially, speed less than 2 knots, recreational fishing, less that 6 knots ?? (typically 5 knots trolling)
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Old 24-09-2019, 10:22   #22
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Re: Advantage of Class B+ AIS on a sailboat?

I may not been seen at 30 NM, but I can see them a coming and set my alarm at 9 NM, Last winter had a Disney Cruise Ship turn into me at 1 KM distance AND they confirmed they saw me clearly. I prefer to be out of the way as opposed to rely on other ships vision and 'attention' particularly offshore in the middle of the night.
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Old 24-09-2019, 14:58   #23
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Re: Advantage of Class B+ AIS on a sailboat?

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I don't know how tall your mast is, but 20NM shouldn't be far from the combined radio horizons. Quite an impressive value especially trough a splitter and a channel 16 optimized antenna. Seems I don't need to look any further than the good old Class B...
Our mast, including antenna is 63 feet
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Old 24-09-2019, 16:46   #24
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Re: Advantage of Class B+ AIS on a sailboat?

I'm in the group who cares more about being able to receive than to broadcast and for this, height of the antenna is the most important parameter. The math is simple because the frequency is line of sight regardless of power and "sight" is .555 miles per foot of elevation. My 47 ft mast can see and broadcast to a horizon 26 miles away. If a big ship has an antenna 100 ft up it's not going to result in more than 75 miles of range because atmospheric issues become the problem and power is the only way to push a signal through moisture in the air. So more power definitely is a positive and I'll install it if I can - at the top of the mast.

But really, if I'm snoozing I want the alert to go off as soon as possible and that is going to be a function of the OTHER guy's power, not of mine.
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Old 24-09-2019, 16:58   #25
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Re: Advantage of Class B+ AIS on a sailboat?

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I'm in the group who cares more about being able to receive than to broadcast and for this, height of the antenna is the most important parameter. The math is simple because the frequency is line of sight regardless of power and "sight" is .555 miles per foot of elevation. My 47 ft mast can see and broadcast to a horizon 26 miles away. If a big ship has an antenna 100 ft up it's not going to result in more than 75 miles of range because atmospheric issues become the problem and power is the only way to push a signal through moisture in the air. So more power definitely is a positive and I'll install it if I can - at the top of the mast.

But really, if I'm snoozing I want the alert to go off as soon as possible and that is going to be a function of the OTHER guy's power, not of mine.
Why would you not care to broadcast - seeing you means the other guy can take evasive action if he needs to
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Old 24-09-2019, 19:08   #26
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Re: Advantage of Class B+ AIS on a sailboat?

It seems everyone here has a good grasp on the topic: antenna height matters more than power, Class A is a hassle, etc.

I have a Class A on board, but only because I was able to acquire one cheaply that needed only a minor repair that the techs hadn't found.

To take full advantage of it, I needed:

1) A second GPS source (besides its internal GPS)
2) A rate-of-turn and heading sensor
3) A little extra power from my batteries (sometimes more than a "little" more - see below)
4) Attention to setting my navigation status. And, if I have the status set to "underway sailing" and then heave to, I get an alarm saying: "navigation status is incorrect" because it interprets my slow speed as not being underway. I ignore that alarm, and the AIS status is changed automatically to "stopped," which technically isn't correct. There is no way to force the "underway sailing" status.

Also, in a seaway with swells, swell motions: sway and yaw, are interpreted as rapid heading changes that cause my packet transmissions to be sent as often as once every 2 seconds. In those conditions, there definitely is more power consumption. The Class A transmission rate algorithm associated with vessel rate-of-turn definitely didn't accommodate a small vessel's rapid swaying and yawing.

I would positively NOT buy a new AIS transponder that uses the old CSTDMA protocol because nearby RF noise will inhibit it from transmitting. I had that happen until I isolated a noisy LED that caused it to stop transmitting whenever the LED was on. Get one of the new SOTDMA protocol Class B transponders that doesn't depend on detecting silent time slots and gets its own time slot assignment.
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Old 24-09-2019, 19:54   #27
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Re: Advantage of Class B+ AIS on a sailboat?

In answer to the question: "why transmit?" -- I've many times gotten calls initiated by other vessels that I doubt would have been made if the other vessel couldn't determine my vessel name. Those calls contributed to safety.

I've also been called by name by the Coast Guard Sector when they saw my position and needed assistance with SAR missions.
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Old 30-09-2019, 09:26   #28
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Re: Advantage of Class B+ AIS on a sailboat?

Before I moved to the dark side, I had a sailboat, and sailed in Elliott Bay in Seattle. With standard Class B, I was not getting seen by the various ships that move around in the bay and north/south.

I upgraded to an AMEC SOTDMA 5W AIS class B+ transponder and that issue became less of an issue.

While I agree with several other folks that your vigilance in staying safe is priority number one, and that you should be on the watch for everyone else, not relying on AIS to tell them who/where you are, I think we can all agree that more visibility across the board, for everyone, is also a benefit.

I'm using a Digital Yacht AIT2500 on the new boat, and it seems to be working just as well, if not a bit better than the AMEC.
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Old 30-09-2019, 10:10   #29
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Re: Advantage of Class B+ AIS on a sailboat?

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Before I moved to the dark side, I had a sailboat, and sailed in Elliott Bay in Seattle. With standard Class B, I was not getting seen by the various ships that move around in the bay and north/south.
Something was seriously fishy there...
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Old 30-09-2019, 12:20   #30
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Re: Advantage of Class B+ AIS on a sailboat?

I'll chime in on my most recent experience.

But first...I've done a lot of sailing in Puget Sound and Salish Sea with Class B w/ dedicated antenna. Never had a problem being seen by other boats. But, also staying out of the way of big ships in Puget Sound has never been an issue by anyone paying attention. IMHO...it was a "nicety" in Puget Sound and mostly noise.

WRT to ocean/coastal sailing...

I lost my forestay 850 miles off the west coast. I had to backtrack to SF under main sail. The ships were few and far between until I got closer to SF. In each case, when a ship got within 5 nm I would contact them via VHF and inform them I had limited maneuverability. In each case but one, the ship informed me of their course change. In one instance a Panamanian cargo vessel did not alter course after I contacted him and he confirmed he "saw" me. I radioed him again when I did not see him alter course and he was within 3 nm of my position. I again informed him I had limited maneuverability, and this time he confirmed my inability to maneuver and said he would alter course to his port.

Moral of the story...don't depend on being "seen" with AIS alone; especially at night. And even if you are "seen" it may not mean the other vessel will take evasive action.

In a crowded coastal waterway AIS to me is less important than "eyes on" unless there is limited visibility (in which case I am using radar). For me, in busy waterways relying on eyesight and vigilance is more important. In some areas of the world boats may not have AIS but will usually at least have a light on at night.

In the ocean/coastal cruising, IMHO AIS is critically important for 3 reasons.
1. So you can "see" and contact other vessels if needed.
2. When I sent out a "pan pan" the USGC asked if I had AIS and asked MMSI, then asked if I had EPIRB and asked for number. They tracked me back to SF until I made contact with them to let them know I made port. (BIG THANK YOU TO USCG District 12).
3. Some countries now require vessels to have AIS.

BTW...I did upgrade to a B+ with dedicated antenna, and also have a AIS receiver built into my Standard Horizon VHF radio as backup.
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