How to check if AIS is transmitting??

[RichandHelen]

There is another app called "Shipfinder" that you could try.

[toddster8]

Within the Marinetraffic website, you can check the location and status of nearby ground stations. A local ham runs the only one near me, and it is not always turned on. If you click on a ground station, it shows you the historic data for that station. Try looking at the data boxes for vessels near you and checking the "ais source."

You can also search your own MMSI on various on-line databases, and it will tell you when and where your signal was last detected. You have to pay extra for this sort of historical data at Marinetraffic.com, but some free databases have a limited amount.

[Seagirt]

Ok, sounds like contacting a nearby vessel is the way to go. I was (and am) a little fuzzy on how the system works. I wasn’t sure if marinetraffic.com would pick up my transmission as readily as any other vessel (if all signals had to go through via a satellite) or if ais info is transmitted ship to ship. Thanks

[Seagirt]

Haha, one thing at a time! Dsc is next on my list.

[Seagirt]

Originally Posted by David Sandowich

As a sailor who also operates a marine traffic station the advice above is correct. Their stations are varied in height and in line of sight often creating gaps. If you are using a splitter and have your VHF on then often your ASI signal is not going out as transmission on the VHF is using the antenna. Also most Class Bs operate at 2.5 watts verses 25 watts on Class C ... a big difference. FWIW ...Ray Marines new AIS700 transmits at 5 watts.Bottom line.... AIS was meant for ship to ship not ship to Marine traffic.

Thanks! That info clarifies a few things. I am using a splitter and was wondering if that could be part of the issue but I figured if I was receiving information from class A and B AIS I should be fine transmitting too. Maybe i’ll Keep my vhf off at least to check if I’m transmitting or not.

[GILow]

Originally Posted by Seagirt

Ok, sounds like contacting a nearby vessel is the way to go. I was (and am) a little fuzzy on how the system works. I wasn’t sure if marinetraffic.com would pick up my transmission as readily as any other vessel (if all signals had to go through via a satellite) or if ais info is transmitted ship to ship. Thanks

One sanity check you really should make...

Look at marine traffic and check if it shows any boats very close to where you are at the marina. If it does show other boats, but not your boat, then you may have signal issue with the unit. Either the device itself, the wiring, the antenna or the antenna placement.

The idea of checking with other AIS equipped boats is good, but you really want to get a sense of the range of the unit, it is not good enough to say that it is working or not. A NEARBY boat may see you, but not one that is five miles away.

I have recently been tracking a pair of boats heading around Australia and I have had a chance to see just how much difference there is in range between a good setup and a not-so-good setup, with one of the boats disappearing from all but the satellite view a good 10 miles or so sooner than the boat it is traveling with. Needless to say I have been asking questions of both boats, and it seems the biggest difference is the antenna placement, with the better signal boat having its antenna at the top of the mast, and the other having it's antenna on the stern rail.

[Sailmonkey]

Originally Posted by Seagirt

Thanks! That info clarifies a few things. I am using a splitter and was wondering if that could be part of the issue but I figured if I was receiving information from class A and B AIS I should be fine transmitting too. Maybe i’ll Keep my vhf off at least to check if I’m transmitting or not.

Don’t turn it off!! It’s only hogging the antenna when it’s transmitting (Keyed up).

[Seagirt]

Originally Posted by GILow

One sanity check you really should make...

Look at marine traffic and check if it shows any boats very close to where you are at the marina. If it does show other boats, but not your boat, then you may have signal issue with the unit. Either the device itself, the wiring, the antenna or the antenna placement.

The idea of checking with other AIS equipped boats is good, but you really want to get a sense of the range of the unit, it is not good enough to say that it is working or not. A NEARBY boat may see you, but not one that is five miles away.

I have recently been tracking a pair of boats heading around Australia and I have had a chance to see just how much difference there is in range between a good setup and a not-so-good setup, with one of the boats disappearing from all but the satellite view a good 10 miles or so sooner than the boat it is traveling with. Needless to say I have been asking questions of both boats, and it seems the biggest difference is the antenna placement, with the better signal boat having its antenna at the top of the mast, and the other having it's antenna on the stern rail.

Interesting info. I definitely need to get out into the open and touch base with some other boats. I'm in a bit of a secluded area and have to rule out a possible line of sight issue. My antenna is on my mast but the hills are higher. I expected a satellite to pick me up but putting myself within view of a land station might be the ticket...

[Seagirt]

Originally Posted by toddster8

Within the Marinetraffic website, you can check the location and status of nearby ground stations. A local ham runs the only one near me, and it is not always turned on. If you click on a ground station, it shows you the historic data for that station. Try looking at the data boxes for vessels near you and checking the "ais source."

You can also search your own MMSI on various on-line databases, and it will tell you when and where your signal was last detected. You have to pay extra for this sort of historical data at Marinetraffic.com, but some free databases have a limited amount.

That's cool about the historic data for the ground station, thanks! I can't find my boat (Longfin) but that'll be a place I keep checking until I figure this out.

[Cpt Pat]

Seagrit, this may not help you because you're in Canada, but for others in the US, the Coast Guard has a validation database of received AIS stations. It will also validate the data configuration of your AIS transponder.

It's here: https://www.navcen.uscg.gov/aisSearch/index.php

Your vessel must have had passed within range of a CG station sometime in the recent past (the CG keeps the records for a while), and the validation only runs once a day, but you'll get both a go/no-go result on reception by the CG and a validation of the vessel data configuration. If you want to see a sample output with no reported errors, run a lookup on my MMSI: 367431840, then click the "view" link for details. I have a Class A station. If yours is a Class B station, it won't show as many details (draft or positioning system).

I tried several antenna splitters. They all failed in one way or another. I finally installed a dedicated antenna - which cost less than any of the splitters. Duh!

Here is another graphical display of AIS stations, though the receivers aren't anywhere nearly as well deployed as marinetraffic's. https://aprs.fi

[GILow]

Originally Posted by Seagirt

Interesting info. I definitely need to get out into the open and touch base with some other boats. I'm in a bit of a secluded area and have to rule out a possible line of sight issue. My antenna is on my mast but the hills are higher. I expected a satellite to pick me up but putting myself within view of a land station might be the ticket...

Satellite reception should detect the boat if the AIS is working properly, but it will appear on Marine Traffic as something like "Pleasure Craft", without a name, unless you are paying for the satellite feed subscription (Not cheap, at least, not by my standards.)

[JPA Cate]

Actually, I think the best info he can get is from other boats sailing in the vicinity, if it is open ocean.

For example, there was a vessel on our trip from Byron Bay to Southport today, whose AIS signal we at first picked up when he was ~ 12 miles ahead of us. However, he got round a headland at ~6 mi. and his signal disappeared for a long time from our AIS. Eventually returned. I'm willing to bet he has a low elevation antenna, or something loose. I would rule out something loose, because it was blowing 25-30, and bouncy, I think it was position.

We have a friend headed this way, *soon*, who used to be picked up at roughly 8 n. mi. but now, only at 2. Dirty connections, not placement.

Both can interfere with who sees you and when. We know a 31 ft. Hunter whose signal is not findable, over about 4 n. mi. I suspect location of antenna.

However, you gotta be out there, and ask for AIS checks. Some of the VMRs use AIS to see if "their" boats are coming on schedule.

In case someone doesn't know, both VHF and AIS are "line of sight", so being behind a headland can block a signat, or down in a gulch between cliffs, also. Especially if all you have is a rail mount antenna.

Ann

[GILow]

Originally Posted by JPA Cate

Actually, I think the best info he can get is from other boats sailing in the vicinity, if it is open ocean.

...

I dunno Ann, I've been watching those two boats from my marina making their way to your part of the world and comparing their reception from the ground based stations, which eliminates one big variable. The results have been very consistent when comparing the two AIS installations. (And a dramatic difference too.)

[El Pinguino]

Checking one's stuff on Marinetraffic.com is fairly simple ....

Go to Marinetraffic when your AIS is transmitting....
Zoom in to your location.... filter for pleasure vessels to make life easier..
Look for your boat....If you are in a very remote location you may not show up but east coast Vancouver Island seems well covered by shore stations
Or enter your boat name into the search box top right..

Once you have found your boat look left under 'Latest Position' and below that 'AIS Source'... click on that and you will go to a page with details of the station that is receiving you...
From that you can calculate your distance from the station.
Take care here... note the height of the station...if they are on top of a mountain results may be a bit misleading.

Example... without logging into Marinetraffic I can use the search to find my boat ... details of last port ATD and present port ATA from late last year, time and position when last received..... May this year was last time my AIS was turned on.... and details of the receiving station...

[Cpt Pat]

Originally Posted by JPA Cate

Actually, I think the best info he can get is from other boats sailing in the vicinity, if it is open ocean.

For example, there was a vessel on our trip from Byron Bay to Southport today, whose AIS signal we at first picked up when he was ~ 12 miles ahead of us. However, he got round a headland at ~6 mi. and his signal disappeared for a long time from our AIS. Eventually returned. I'm willing to bet he has a low elevation antenna, or something loose. I would rule out something loose, because it was blowing 25-30, and bouncy, I think it was position.

We have a friend headed this way, *soon*, who used to be picked up at roughly 8 n. mi. but now, only at 2. Dirty connections, not placement.

Both can interfere with who sees you and when. We know a 31 ft. Hunter whose signal is not findable, over about 4 n. mi. I suspect location of antenna.

However, you gotta be out there, and ask for AIS checks. Some of the VMRs use AIS to see if "their" boats are coming on schedule.

In case someone doesn't know, both VHF and AIS are "line of sight", so being behind a headland can block a signat, or down in a gulch between cliffs, also. Especially if all you have is a rail mount antenna.

Ann

Ann is correct on all points. I'll add some details...

While AIS is line of sight, there are conditions that can allow AIS data packets to propagate incredible distances. Since I've operated a Marine Traffic volunteer receiving station for years (details and stats here: https://www.marinetraffic.com/ais/details/stations/595), and I'm logging reception distances, my record "DX" (distant operation) is 12,000 miles - essentially the other side of the planet. These single packets, which are only 20 milliseconds in length, can travel hundreds of miles during periods of atmospheric ducting caused by thermal inversion layers that act as a mirror, much like thermoclines in the ocean reflect sound back at the bottom (an effect well known to submariners to evade sonar detection). Single packets thousands of miles distant can also reflect off ionized meteor trails. So if you see a vessel beyond line of sight that appears only intermittently: nothing is wrong. Its signal may have well been refracted to you by the atmosphere - much like during a sunset you can often see a distorted image of the sun minutes after it has actually set. If the atmosphere can do that to light, it can certainly do the same to VHF. The effect is only temporary.

Only by asking for an AIS check with several vessels can you get a feel for your transmission range. With an old protocol (CSTDMA) 2.5 watt Class B transmitter, I wouldn't be disappointed with a range of 4 miles, and 6 miles with a newer 5 watt SODTMA transponder. Doubling the power does not double the range. At best, it only increases the range by a factor of 1.41 (the squared-root of 2). Your range is mostly constrained by your (and the receiver's) antenna height above the water. You'll get the greatest benefit by raising the antenna - not the power.

If your vessel appears on Marine Traffic, you only have confirmation that it is transmitting - but nothing else about your transmission effectiveness (antenna, coax, etc.). You need to examine where that receiving station is located, its antenna height above MSL, and the receiver type - some receivers are just cheap insensitive scanners with very basic antennas (only receiving strong signals) while others are actual AIS transponders that will receive very weak signals. If its a cheap receiver - that's good. You have to be pounding on that receiver to be heard at all.

Don't be disappointed if Marine Traffic never reports your vessel via satellite reception. Far fewer Class B transponders can be heard by satellite than the Class A transponders. The Class As tend to drown them out at satellite altitudes through contentioning over the available time slots.

My own station (my actual AIS transponder) is so sensitive that it will report vessels in my harbor that may have serious defects in their antenna (I was plotting one that had lost its antenna entirely) due only to proximity. You can get the receiving station details (on a web browser - the smartphone app is different) by clicking on the vessel, looking at the displayed data block, and then clicking the link for the receiving station number at the bottom. There you will see the receiving station details in the upper right corner.

If you want to verify your transponder data was properly configured (depressingly, many are not), you can use the CG link I posted above in this thread. You only have to have come within reception range of a CG AIS base station once within the recent past to have an entry in that database. You can see the locations of CG AIS base station on Marine Traffic. Thy appear as yellow towers (provided you haven't filtered them out).

73
N8QH