Strange AIS behaviour

[Rob_Webb]

I’ve bought a boat in Asia and the local skipper looking after it says the AIS is working - both sending & receiving. The plotter screen looks normal showing other vessels and my own boat’s AIS signal can be seen on other boats’ screens.

But when I search for it on the Marine Traffic website it only shows an old position report from about 2yrs ago. Even though my new boat has moved in the last month (all be it only a few miles and not far).

Anyone know what’s going on?

 

[Iliade]

Maybe you are not transmitting with enough power to reach the Marine Traffic receiver(s).

How far away were the boats that could see you?

 

[mikegunn]

I’ve bought a boat in Asia and the local skipper looking after it says the AIS is working - both sending & receiving. The plotter screen looks normal showing other vessels and my own boat’s AIS signal can be seen on other boats’ screens.

But when I search for it on the Marine Traffic website it only shows an old position report from about 2yrs ago. Even though my new boat has moved in the last month (all be it only a few miles and not far).

Anyone know what’s going on?

Marine Traffic is a useful App but does have limitations. It gleans AIS transmissions mainly via a world wide network of shorebound listening stations. Presumably your vessel is transmitting AIS type B, with a modest practicable range of around 5 miles. I have found many coves and anchorages where my transmission has been blanketed from a listening station by local topography. The important thing and incidentally the whole purpose of AIS, is that nearby ships can see you and you see them.
Mike

 

[Rob_Webb]

Interesting points thanks.

But I hope I’ve not got a weak VHF / AIS antenna and / cabling...

 

[DJE]

Have you tried Vessel Finder or any of the other AIS web sites? They use different listening stations so some are better than others in some areas.

 

[mikegunn]

Interesting points thanks.

But I hope I’ve not got a weak VHF / AIS antenna and / cabling...

You can easily check, by identifying the furthest vessel from you that is transmitting type B. Give them a call on VHF, preferably using DSC and ask them if they can see you. They’ll probably be very pleased to hear from you, because it will let them know that they’re transmitting.
Mike

 

[RichardS]

Have you tried Vessel Finder or any of the other AIS web sites? They use different listening stations so some are better than others in some areas.

+1

You might well find that you appear on Vessel Finder.

Richard

 

[greeny]

Interesting points thanks.

But I hope I’ve not got a weak VHF / AIS antenna and / cabling...

[/QUO[/QUOTE]

Probably not. It happens to me all the time. Especially when at anchor or in marina. The land based antenna for picking up ais and sending the info to the web based systems are often no longer line of sight to you due to land mass and this causes the loss of your signal to them. One thing is for certain, height is everything in these situations. My antenna is on my pushpit and the shore antenna can go hours even days between picking me up as a signal. If I pull it up the mast on a flag halyard it picks up immediately. Mine will stay on the pushpit though because it works fine when it matters, out at sea, between myself and ships.

 

[duncan99210]

One of the reasons I fitted AIS was so that the kids could keep track of my whereabouts via Marine Traffic et al. It’s a busted flush, sometimes it shows up our real time position, other times it can go days without updating. The AIS works just fine, other friends on their boats can pick us up, as we can pick them up but Marine Traffic sometimes shows us but not our friends and vice versa.
When I first fitted the kit, I was convinced for a short while that it wasn’t working because Marine Traffic didn’t show us: called up a friend who I could see on my screen and he could see me... Taught me not to rely on the app for position information.
When we next make some longer trips, I’ll be getting a Gramin InReach to let people back home keep track of where we are.

 

[Rob_Webb]

Yes I’ve tried a couple of the others and they don’t even show the boat at all - at least Marine Traffic shows my boat albeit a position about 2yrs ago.

I’ve also noticed from usage on my previous boat that my position was always showing accurately in real time on Marine Traffic - possibly due to both my antenna being at masthead plus my AIS always being switched on - even at rest. I wonder if the system regards ‘always on’ AIS as frequent users hence always updates them in real time.

In contrast some of my friends who switch theirs off every day would sometimes have huge lag of many hours in their position reports even when switched back on.

Is that a thing?