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Old 05-08-2016, 07:13 AM   #1
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AIS and relevance to safety

An observation, from our trolling experience yesterday.

A relatively small powerboat crossed our bow yesterday at a reasonably high rate of speed, perfectly safe crossing... no problems. FWIW, it was named "Outrage" in its AIS transmission, so I make the guess that it may have been a Boston Whaler of that model.

I watched him visually, and also tracked him on the radar... and I was also able to follow him on the chartplotter via his AIS signal. (Not so common around here to see AIS on a small-ish vessel such as this... at least not so far).

His last transmission immediately before crossing in front of us was about 1/4-mile out at about 10 o'clock. His next transmission was about 3/8ths of a mile out at about 2 o'clock. IOW, he was traveling at about 5/8ths of a mile between AIS transmissions, and he crossed ahead of us -- and then some -- within the space of those two transmissions.

Visibility conditions were adequate. This was shortly after daybreak: cloudy, overcast, and slightly foggy in some areas... but nav lights on all the various vessels in sight were clearly visible, and visibility wasn't particularly hampered by weather conditions. The fishing crew I had aboard we're doing their thing at the time, with no significant input needed from me... so I was able to keep a sharp lookout with no distractions.

His track on the radar was obvious, although even that was a "dotted line" formed by multiple returns from the open array set to .5 NM max.

In significant fog, he may not have been visible to the Mark I* Eyeball at all those distances... and in heavy pea-soup, I wouldn't have been able to eyeball him at all. (And he likely wouldn't have been traveling at that speed in conditions like that.)

-Chris
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Old 05-08-2016, 11:56 AM   #2
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Remember AIS is a "tool" to help you find targets or show you as a target. Just one tool in the tool box.
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Old 05-10-2016, 07:06 AM   #3
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I purposely didn't add any "conclusion" or "deduction" or whatever...

But yes, that's always been my take on AIS.

In that situation, Mark I* Eyeball was best, radar second, AIS interesting. In fog, that likely would have been radar best, AIS maybe or maybe not immediately useful, Mark I* Eyeball maybe or maybe not useful... both of the latter depending on how dense the fog might have been.

I do like having AIS, though. Even when trolling on one engine at very slow speeds, trolling valve engaged, steerage sometimes precarious... I can often, and easily, work with oncoming traffic to sort out my best (easiest for him) course if we'll end up close to each other.

That's especially true for tugs and so forth, since they don't much stick to the main channel around here. That kind of conversation usually starts when he is a couple miles out from me...

-Chris
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Old 05-10-2016, 09:12 AM   #4
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I come close to installing several times, however other things took presidency. Also I am not so sure it would be that useful for the area and fair weather cruising we do as most ships commercial boats and ferries tend to follow a route channel lane. Also very few pleasure big and small have. However I did upgrade the electrinic charts soltware and a new pc, so when the vhf radio needs replacing it will be added. Maybe this year or next. Radar is still my primary which has worked for 20+ years.
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Old 05-10-2016, 08:04 PM   #5
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Yeah, can't really use AIS for real-time tracking in close quarters, but I'd still not be without it now (well, not at our current marina at the moment, I think we might be the only boat in the entire marina and this part of the MO River that has it). After our run last summer from Newport to Albany though, real water, I wouldn't be without it. Gives approximate locations and lots of vessel info, very useful and very reassuring in a lot of ways. Lowered my stress level at least a little in New York Harbor.
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Old 05-16-2016, 09:37 PM   #6
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Although it's really pricey; If you can afford it get a class A. Versus a class B. The A units transmit better, more reliably and more frequently. The lag you saw (IMHO) is a class B unit with a longer 'off' time between transmissions. Even the difference between 10 seconds versus constant transmitting is telling in close quarters when in fog.
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