AIS surprise

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cpedw
Old Salt
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Joined: Fri Aug 20, 2004 11:38 am
Boat Type: Nordship 35DS
Location: Oban

AIS surprise

Postby cpedw » Sun Sep 22, 2019 4:28 pm

Having been scarily enveloped in fog twice in the last two years, both times in the Firth of Lorn outside Oban's north entrance, I fitted AIS last winter to improve information for the next occurrence. (Nothing similar has happened this year so it has worked!)

But last weekend, when passing Lochaline entrance, the ferry Lochinvar turned up on the AIS and visible too. It was going backwards according to the AIS symbol on the chart plotter. Careful analysis of all the data available showed that its heading was about 180 degrees different from its COG. I presume that Lochinvar has a choice of front ends. It looks like that but I thought that, like Coruisk which looks double-ended but actually has only one front end, there would be a front and a back. It seems Lochinvar's heading sensor is the only part that has only one front end. Can anyone confirm my suspicion or offer an alternative explanation?

Derek

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pagoda
Master Mariner
Posts: 225
Joined: Sat Jun 18, 2011 1:17 pm
Boat Type: Jeanneau 42iPerformance
Location: Near Montrose, boat on the Firth of Clyde

Re: AIS surprise

Postby pagoda » Sun Sep 22, 2019 6:34 pm

Catriona which runs between Lochranza and Claonaig on Kintyre does exactly the same.
We came up from Campbeltown a few days ago and saw the wee ferry apparently going backwards (by AIS) across the Kilbrannan Sound at 9Kts.
It does look weird on the plotter mind you!

Burst Boiler
Able Seaman
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Joined: Sun Sep 16, 2018 12:57 pm
Boat Type: Bavaria

Re: AIS surprise

Postby Burst Boiler » Mon Sep 23, 2019 9:45 am

There's a marine guidance note MGN 321 on the mca website about this. Apparently the software with some commercial ais kit was hard wired to a single heading indicator that meant the forward direction for ais couldnt be switched. So COG is fine, but heading is 180 out. The MGN states this must be fixed, usually by means of a switch that also sorts out the lights and horn direction. This should all have been fixed by July 2006 so I suspect the skipper just forgot to change it at last turnaround. I've seen one with the wrong lights on too.

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mm5aho
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Re: AIS surprise

Postby mm5aho » Mon Sep 23, 2019 8:05 pm

Loch Dunvegan (Colintraive) sometimes has this problem too, though its torturous windy lengthy course probably renders it unimportant!
Geoff.
"Contender" Rival 32: Roseneath in winter, Mooring off Gourock in summer.


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