New price point for AIS class B+

[Dockhead]

Originally Posted by mikedefieslife

Is that really true though? Most of use with 3/4g radars can happily pick up 5m fishing boats and other small pleasure craft.

In bad weather the result might be different, but then that is exactly the type of weather these small craft won't want to be around in.

Yes, it's really true, and frequently mentioned by pro mariners. And if it weren't so, radar reflectors would not exist, much less active radar reflectors like SeaMe. Plastic boats don't reflect x band radar very well even in good conditions (3/4G radars are Continuous Wave, which is a different principle, and do this much better), and small yachts like ours easily disappear in sea clutter.


It doesn't take really "bad weather" to create enough sea clutter to "disappear" a small boat. Just 2 meters or so, which most of us go out in regularly.

[Cpt Pat]

Originally Posted by Dockhead

Small plastic sailboats show up poorly on radar, even big ship radar, and MOST radar reflectors are basically useless (see the test some years ago in PBO). So you really don't want to count on ARPA, for ships to see and evaluate risk of collision situations with you.


If you are never in heavy traffic, then, as I said, you will not care much, but different waters have wildly different conditions, so YMMV.

In my waters, AIS solves only about half the problem of being seen in my local conditions. Close into harbor, most of the aging commercial fishing fleet isn't equipped with AIS.

I've read the test reports on radar reflectors and also been at the helm of small commercial fishing boats trying to find my way around in fog - with no AIS - using the typical 10 to 20 year old X-band radar (without MARPA/ARPA capability) carried aboard those vessels. The radar reflectors on fiberglass sailboats produce only small intermittent targets.

The two good things about passive reflectors are: 1) they are cheap, and 2) they require no power. Beyond that, they are not very effective for collision avoidance. Lab tests show that few reflectors even meet their 10 square meter reflectivity claims, and some are all but useless. Here is one good report on radar reflectors: https://www.ussailing.org/wp-content...ector-Test.pdf

On a typical day, the waters around my harbor are saturated by 30 to 50 foot commercial fishing boats. Few are equipped with even AIS receivers, and less than a dozen transmit AIS. But they all have radar (X-band radar - none have S-band radar), and when the visibility frequently drops to less than 300 feet, the helmsman is using nothing but radar for collision avoidance, while only occasionally glancing at the chart plotter for navigation. Predicting when the fog will develop is no easy task, and if you are out and want to avoid returning to port in fog - you may be stuck out for several days.

Just a few miles to seaward is large cargo traffic. Presumably, all those vessels have AIS in addition to X-band radar. Below is a map of the traffic with AIS transiting in one day (produced by the AIS receiver on my boat). It's not the English Channel, but it's busy.

To be seen by those fishing vessels, in addition to having AIS on board, I also have an Echomax active radar target enhancer (RTE) that produces an equivalent reflectivity of 100 square meters. I have the RTE mounted 4 meters above the water line. It can also beep at me to warn that I'm being painted by X-band radar, which is useful in letting me know there's another vessel with radar (but possibly not with AIS) within about 10 miles.

[CaptTom]

Bit of thread drift going on, but I think it adds to the discussion.

A radar reflector, IMHO, is an absolute minimum requirement. But I still see boats with those old-fashioned "plastic tube" reflectors being used.

Those are virtually worthless.

Pat linked to one study (not sure if it's one I've read before or not) but you can Google for others. Those tube things always test out at the bottom of the list.

After reading all the research, my solution was to go down to the commercial fishing supply store and buy a cheap diamond-shaped aluminum reflector. You can get small ones the fishermen use as high flyers on their gear. I got a bigger one, but it was still very inexpensive compared to what they sell at the "yottie" stores.

Then, I mounted it in what one study called the "catch rain" position, not with the point up. I'm told my boat looks huge on radar.

[GTom]

Originally Posted by Tillsbury

I still don't quite get what significant advantage the B+ units have in the real world. It seems that all they are going to do is make it less likely that your boat will be found in the wrong place by others, when you are in a very crowded area. They don't make seeing others any better (as if others are class B they may also be delayed in a crowded area, and if class A they'll be visible whatever happens).

Under what situation are you relying on someone else finding you accurately on AIS, given that you're in a very crowded area and therefore at close quarters in a busy waterway?

I use AIS to see where and how fast the big ships are going when they're coming into and going out of harbour (and where they'll be in the future compared with my track). And I use AIS to see anyone within any distance when I'm out at sea (and I hope that I am more visible to them because of AIS). I don't care less how accurate the AIS position of another sailboat is (who is likely to be class B if they have AIS at all), because at close quarters I will look for him by eye.

I'm a bit of a tech nerd so I'm sure I would end up buying a B+ just for the sake of it if I didn't have AIS already, but I really can't see what its advantage is for a sailor.

1. The stronger B+ signal can be picked up by AIS satellites: with a subscription, your family/friends can follow your progress - or in case you have to abandon a functional boat for whatever (medical, etc) reason, salvors can save it.

2. In really busy areas you won't disappear from a ship's target list thanks to the higher update frequency

3. Thanks to the stronger power, cable and splitter losses won't matter

[continuouswave]

Originally Posted by GTom

1. The stronger [Class-B SOTDMA] signal can be picked up by AIS satellites

The difference in transmitter power between Class-B SOTDMA (5-Watts) and Class B CSTDMA devices (2-Watts) is 4 dB. While there is no doubt that increased transmitter power will always improve the received signal in a given propagation path, I don't think you can establish with any certainty that Class-B CSTDMA devices cannot be received or will never be received by receivers aboard orbiting satellites.

If the goal of transmitting AIS is to improve the chances of the signal being detected and analyzed by an orbiting satellite, then the boat owner should move up to Class A devices at 12.5-Watts. The improvement over Class-B SOTDMA is another 4-dB, for a total improvement compared to Class-B CSTDMA devices of 8-dB. This puts that boat's AIS on an even footing with commercial vessels that are routinely received by satellites.

If there were a bias against AIS Class-B CSTDMA signals being received by orbiting satellites, it might be due to the slightly altered timing of their signals, more so than a 2.5 dB lower signal level. Because satellite AIS receivers can receive AIS signals from multiple self-organized networks which are not inter-coordinated, those signals often are analyzed by sophisticated methods to reduce the effects of packet collision. It is hard to know if the de-collision algorithms might affect the ability to find packets sent from Class-B CSTDMA transmitters.

Also, I am not aware of any limitation on antenna gain in AIS transmissions, and a disadvantage of 4 dB could be compensated by using more antenna gain. Of course, antenna gain comes at the expense of antenna pattern. A more concentrated antenna pattern might work against satellite reception for satellites appearing at high elevation to the transmitter antenna. Maybe one ought to use a special antenna with a high lobe to skyward for best AIS reception by satellite.

Probaby the best advantage to be gained for reception of AIS transmission by satellite is to invest in one of the newer proprietary AIS transmitters that uses an enhanced signal algorithm, developed by SRT.

[Alterboy 65]

I am interested in how you make out also .....
I have a 2012 Raymarine AIS 650 Class B and I have been having trouble transmitting since I bought it. It moves to silent mode no matter what you do . Yesterday a marine electrician said the problem was that I have a passive VHF Splitter . That I need an Active 12 v splitter to send out the signal for the boat. Has anyone heard anything about this and do you know where I can get such a splitter for This unit. The same electrician said they dont make them anymore . Any help greatly appreciated .

Alterboy 68

[powsmias]

no ebay feedback on the seller

[flyingnut40]

AIS unit has been released from RU customs and is enroute to Canada. I'll have more info to post when it arrives. Stay tuned and you can all laugh at my expense then..... smile.......

[flyingnut40]

Alterboy,
I would seriously give up on the splitter idea, never a good compromise under the best of situations. Just wire it to a decent antenna and remove the extra failure points. For testing you could wire direct to your VHF antenna and know for sure. If you are having splitter issues that make the system shut down..... even a simple 1/4 wave antenna on a solar arch or railing is going to serve you better. You can have 7/8
The range of mast top or nothing..... I know what I would do...... separate antennas.

[sailing_jack]

look here for AIS devices approved for use in Canada
https://wwwapps.tc.gc.ca/Saf-Sec-Sur...nufacturer_ASC

[flyingnut40]

For VHF work, I prefer my 5/8 wave Motorola Spectrum which I have an extra. You used to see them on every cop car before they went to 800 mhz. Not sure if they still sell them, but they work amazing on the 144-148 mhz ham band and only require a little shortening of the whip to do marine. I'll be putting mine on the arch. Even in the salty north winters, mine has lasted 20 yrs. and counting......

[flyingnut40]

Originally Posted by sailing_jack

look here for AIS devices approved for use in Canada
https://wwwapps.tc.gc.ca/Saf-Sec-Sur...nufacturer_ASC

As a brand new unit I'm expecting.....(fingers crossed) that the appropriate approvals are done and the list is waiting for an update. FCC list is dated by a few months. I'll share the ID numbers when I get it.....if you dont know..... Industry Canada takes approvals from the 6-8 odd testing labs around the world at face value and puts them on their list. They dont test every model themselves.

[ronstory]

Originally Posted by Alterboy 65

I am interested in how you make out also .....
I have a 2012 Raymarine AIS 650 Class B and I have been having trouble transmitting since I bought it. It moves to silent mode no matter what you do . Yesterday a marine electrician said the problem was that I have a passive VHF Splitter . That I need an Active 12 v splitter to send out the signal for the boat. Has anyone heard anything about this and do you know where I can get such a splitter for This unit. The same electrician said they dont make them anymore . Any help greatly appreciated .

Alterboy 68

Alterboy--

You may want to start your own thread for a specific question about a different product than the OPs.

[GBR134]

We use a separate aerial for the AIS on a rail mounted pole. It has the added benefit of acting as a back up to our mast mounted vhf aerial which I consider a considerable bonus.

Our original theory was that on passage we could swap the leads round offshore to increase range of the AIS. In practice I’m picking up most traffic well outside the 12nm range from the pole mounted aerial. I’m not quite sure why I want a warning of a target more than 12nm distant so I’ve never done the swap.

[flyingnut40]

Excellent point!!