AIS Transponder: Yes or No

[CarlF]

Judy, you're right that I don't constantly monitor my AIS transmit, but I do frequently check with passing ships that I'm showing up. There's never been a report of "dropping out" or not seeing me.

I also don't see "drop outs" on my receiver when looking at other boats that are presumably transmitting on class B units. Especially on the ICW, I watch them come and go past me over quite a distance.

Is there a chance that your AIS receiver or installation is at fault rather than the other boat's transmitter? Receiving class B signals is tougher than class A. A marginal setup might behave exactly as you describe (e.g. good reception of Class A and spotty reception of class B).

Carl

[sabray]

Put a Milltech receiver on love it. Worried about overcrowded broadcast. I really like calling x commercial vessel by name and discussing where we are going. Okay I'll hold course I'm sailing so my speed may very. They say thank you captain were pulling up a few degrees have a nice trio. Beats the he'll out of 3 radar blips in Ambrose west bound. The one with all the lights are you continuing course at current speed or are you going to do another 360 loop at eradicate speeds. Yes on a receiver maybe on transponder

[CarinaPDX]

A commercial ship's radar is simply not adequate to pick up small sailboats except in calm conditions. Of course, like the previous comments about AIS, how do you know it is working that well? How do you know how many boats you didn't see? In my experience, not only doesn't ship's radar work well for small boats, the bridge watch doesn't know that it isn't working. (I can hear the howls already.)

How can I say this? When I first left the Pacific Northwest I was actually cheeky enough to call the freighters that passed me and asked if they saw me. Of course most didn't respond to the hail, but about a third did. The typical response was surprise that I was so close (typically a few miles) and that they hadn't seen me. After looking around and not seeing me yet, they would ask where I was and I would give them a relative bearing and distance. A few moments later they would report seeing me. I would then ask if they could pick me up on radar; after a bit of tweaking they would report too light a contact to have noticed. One man suggested I buy a radar reflector (I had a Firdell Blipper at the spreader). Now, to be fair, the conditions were usually 6-8 ft seas for most of the trip south so there was a high noise floor, but the experience was remarkably repeatable. So no, ships don't see us with radar much of the time.

Since commercial ships are required to have AIS, they WILL be alerted to your presence, as well as course and speed. My last Atlantic crossing was really rough; I could barely see freighters just 3-4 miles away due to the seas so I am certain they didn't see me. But they were picking up my AIS, and some hailed me just to say hi and check up. Worth every penny...

As for the intermittent reception issue, I note that the comments came from people with "receivers", which is to say equipment that has not been tested or approved to any standard - unlike Class B transceivers. The assumption that the problem lies with the transmitter and not the receiver needs to be proven. There is much that could go wrong with the reception of a very brief, very low power, digital packet. Even if the transmitter is turned off, I would trust a Class B (approved) receiver any day over the cheap, non-approved, receiver-only sets. My 2¢.

[CarlF]

For a small sailboat in coastal waters, I'd spend the money for an AIS transceiver before a radar (it's cheaper too) Chartplotters do a much better job keeping your from hitting land than radar. And AIS is far superior for collision avoidance with other vessels.

Keeping a good radar watch requires constant attention. The typical sailor glancing at a radar screen while also steering isn't doing a very good job at either.

Carl

[barnakiel]

I am not clear what the second part of the poll query means: "...or only see others how have?"

In any case, we want one.

We have AIS receiver / VHF transceiver combo + PC plotter for now, but would much prefer not only to see but also to be seen.

We had some close calls and one was pretty dramatic. Probably would not have happened with AIS onboard.

b.

[jeffrobbins]

Whether you are received or not is of course a factor of both your transponder and the receiver on the other vessel. As was pointed out, certified Class B transponders had to prove they both transmit properly and have sufficient sensitivity to receive low power signals. They also are tested for durability. A lessor-known requirement is that they must prove they can simultaneously receive on both channels during extreme channel loading. AIS receive-only units don't have any of these requirements and so they may not be receiving your transmissions. I've never tested any of the budget receivers or integrated-into-the-VHF receive-only models, so I can't say whether they would meet the Class B specifications or not.

However, another factor that is often overlooked is the antenna system for your transponder. With most transponders you usually have no way to know if your antenna is actually radiating much, or any, of your signal. A common problem is the antenna isn't well matched for AIS frequencies or cable/connector issues. You can use a standard VHF antenna, but be sure it covers up to 162 MHz with low VSWR and you have well made cables and connections.

Unfortunately, you just can't judge transmission performance by whether you receive vessels far away.

[SailFastTri]

Originally Posted by CarlF

For a small sailboat in coastal waters, I'd spend the money for an AIS transceiver before a radar (it's cheaper too) Chartplotters do a much better job keeping your from hitting land than radar. And AIS is far superior for collision avoidance with other vessels.

Keeping a good radar watch requires constant attention. The typical sailor glancing at a radar screen while also steering isn't doing a very good job at either.

Carl

Carl, that means you won't see or be seen except larger or better equipped vessels. Radar is also a navigation tool that can help you see every type of vessel (except submarines) and a lot of other hard things, including navigation aids that have been moved for changing shoals.

I have both radar and AIS transceiver, and IMHO you should think about this further. They are both useful, but I think radar is more fundamental and essential. In dense fog the radar and C-P are most essential, and the AIS is extra information. It's not going to help you avoid the open console fishing boats out there.

[SailFastTri]

Originally Posted by captainKJ

Personally I think AIS is a waste of money for a sailboat. I sailed supply and anchor boats in the gulf of Mexico. On a commercial vessel they are required. Spending many hours in the bridge most of the boats have 2 radar units. A good reflector is a must. I would rather have a very good reliable radar than an AIS unit. Just a new item for people to spend money on. Radar will tell you were the vessel is and it is easy to call them by giving them lat and long. I know this will start a debate but were are you sailing to and from. It is just another toy to buy. save the money and buy a better radar unit. the more toys you have on a boat the more they will break. Keep It Simple Stupid works wonders.

Yes "it is easy to call them by giving them lat and long" but it is NOT easy to get them to answer to that. I have NEVER heard anyone other than the CG respond to identification by ONLY "lat and long". People don't think that way. You can call them by describing their vessel, heading, and position relative to some other prominent thing or geographic feature, but isn't it MUCH better to call them by name?

The IP of this web site is 173.192.60.130. Google answers to 74.125.226.115. If we had a conversation about multiple web sites do you think it would be more clear to everyone involved if we describe them by name or number?

[captainKJ]

A commercial ship's radar is simply not adequate to pick up small sailboats except in calm conditions

This is the BIGGEST BUNCH OF CRAP I HAVE EVER SEEN. The radar we use can pick up lobster bouys in 4 foot seas. I have worked private yachts, commercial ships and have my own sailboat. I would choose radar before AIS. Make sure you have a BIG radar reflector or 2 onboard your sailboat.

[captainKJ]

Originally Posted by SailFastTri

Yes "it is easy to call them by giving them lat and long" but it is NOT easy to get them to answer to that. I have NEVER heard anyone other than the CG respond to identification by ONLY "lat and long". People don't think that way. You can call them by describing their vessel, heading, and position relative to some other prominent thing or geographic feature, but isn't it MUCH better to call them by name?

The IP of this web site is 173.192.60.130. Google answers to 74.125.226.115. If we had a conversation about multiple web sites do you think it would be more clear to everyone involved if we describe them by name or number?

I have called many ships by name. yes it is better mainly because the watch keeper is most likely looking at his latest iphone app instead of keeping a watch out. If the watch keeper is trained correctly he will know when a vessel calls his lat and long. I have done this many times. true names are better but I was taught before AIS. personally i would not waste the money for it on a sailboat. If the watchkeeper is not watching his radar he sure is not watching his AIS or the screen overlay on the chartplotter

[captainKJ]

The IP of this web site is 173.192.60.130. Google answers to 74.125.226.115. If we had a conversation about multiple web sites do you think it would be more clear to everyone involved if we describe them by name or number?

apples and oranges. web site and AIS are 2 different things.

[Sailor g]

We got AIS before you could get the transponder. We have a tri lens reflector and have had no problem being seen by the ships we have asked. It's great to see how close the big ships will come and when - also to vector their path to us. It's just one more piece of information to use.

[David M]

Originally Posted by SailFastTri

No - a standard VHF antenna works fine. If you don't have a separate antenna you need a splitter.

This was not my experience AND Furuno tech support said I needed an AIS specific antenna for my transceiver. For AIS receivers regular VHF antennas do work fine.

Perhaps this fact is specific to Furuno Class A transceivers and not some other transceivers?

[xymotic]

Originally Posted by CarinaPDX

Since commercial ships are required to have AIS, they WILL be alerted to your presence, as well as course and speed.

Except, they are not required to monitor class B. So they will PROBABLY be alerted to your presence.

[SailFastTri]

Originally Posted by David M

This was not my experience AND Furuno tech support said I needed an AIS specific antenna for my transceiver. For AIS receivers regular VHF antennas do work fine.

Perhaps this fact is specific to Furuno Class A transceivers and not some other transceivers?

The marine VHF spectrum is 156.000 through 161.925 MHz. Marine VHF antennas are tuned to accommodate that fairly broad band. AIS uses two channels at the top of the VHF range: 161.975 MHz, and 162.025 MHz. So while a general-purpose marine VHF antenna isn’t optimized for AIS specific frequencies, it is designed to work very near those frequencies.

No doubt Furuno was giving you good advice to optimize your installation, but if you already have a spare VHF antenna it can be used for AIS with very good results. In a controlled test you could measure a performance difference, but in the real world you'd probably never know the difference without some kind of measurement capability.

If someone could point to a test showing the performance difference with an AIS-tuned antenna vs. a VHF general antenna I'd be very interested. If the difference is more than 15 or 20% I'd be very surprised.

BTW -- my West Marine AIS 1000 transceiver recommends use of a "VHF antenna". It has a self-test diagnostic which would show a red error light and shut down radio transmission if the antenna's VSWR is out of acceptable range (1.5:1). I'm using a standard 3db dedicated VHF whip and have never seen that light, and based on tests using marinetraffic.com and other vessels I know my range is very good and meets "normal" AIS Class B expectations.