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Old 28-10-2013, 16:02   #121
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Re: New Inexpensive Ais Transponder

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NOAA getting out of the paper chart business has it's pro's and con's, but that's more a factor of government issues and technological improvements making Print-On-Demand paper charts in many ways superior to the standard large scale print run of charts. Obviously the popularity of electronic charting is the other major factor, and I fully admit I use electronic charts just about all the time, but trusting my eyes and ears trumps any electronic aid to navigation especially in regions that charts may be either not be of appropriate scale or inaccurate due to age of survey information or typographical error.

Assuming enough electrical generation capability, no water intrusion problems, and not being hit by lighting modern electronics are definitely very reliable especially as it relates to a constant 24/7 watch. Mark I am in no way opposed to electronic aids to navigation, but there is also a number of people that seem predisposed to trusting technology over their eyes and ears. I am lucky to still have good eyes and ears that I can trust whether it be seeing a ship's lights on the horizon or hearing a ship is in the vicinity. Regarding ship traffic, I relatively recently sailed offshore from Alaska to San Fransisco with plenty of ship and recreational traffic at the conclusion of a long passage, and given the increased naviational challenges of busy shipping lanes I anchored out for two nights to catch up on sleep and listened to Vessel Traffic Services as a complement to my eyes and ears. Yes, I will appreciate having AIS information at my disposal as an additional aid to navigation now but it would be foolish to go out at sea without good eyes, ears, and paper charts, with countless other additional tools both electric and non-electric being important additions such as GPS, radar, and binoculars (yes, mark it's amazing how much further I can see with good old fashioned binoculars and if I had to choose I would choose to have a good pair of binoculars over AIS any day ;-) )
bino's don't work well in the fog, ais does. There are times when visibility is very poor, radar isn't always dependable. Redundancy is the best protection against system failure.
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Old 28-10-2013, 16:08   #122
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Yeah SunnySkys comments reminds me of a joke.

Guy parks his car, and a dodgy young fella comes up and says , "I'll mind your car for a tenner mister", "naw" , says the owner, "it don't need minding " , "has it got a fancy alarm then" says the fella," naw , it's got that ", pointing at the big dog inside

Walking away , the fella shouts after him," hey mister , your dog put out fires then" !!

Dave
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Old 28-10-2013, 17:05   #123
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Re: New Inexpensive Ais Transponder

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Yeah SunnySkys comments reminds me of a joke.

Guy parks his car, and a dodgy young fella comes up and says , "I'll mind your car for a tenner mister", "naw" , says the owner, "it don't need minding " , "has it got a fancy alarm then" says the fella," naw , it's got that ", pointing at the big dog inside

Walking away , the fella shouts after him," hey mister , your dog put out fires then" !!

Dave
We were saying the same thing but I like your way better Dave.
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Old 29-10-2013, 06:37   #124
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Re: New Inexpensive Ais Transponder

My point that you seem to not understand is you cant use AIS for collision avoidance in the real world as it doesn't give you the information you actually need to apply the rules.
AIS was never intended to be a tool for that ( hence the name)but for a vessel without radar you certainly get information you didnt have before.
You are trying to wish AIS is something it is not
The implementation on commercial vessels can be a 3 line display, who's going to be reading that when on watch
AIS was implemented to allow ports to identify ships
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Old 29-10-2013, 08:08   #125
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Re: New Inexpensive Ais Transponder

In the apparently non-real world where I sail, AIS gives me information that is extremely useful for avoiding collisions. I will continue to use this information, as well as my radar, compass, eyes and ears.
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Old 29-10-2013, 08:29   #126
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My point that you seem to not understand is you cant use AIS for collision avoidance in the real world as it doesn't give you the information you actually need to apply the rules.
????

Rule 7 d i
(i) such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change;

AIS will show if that is happening, usually before the other vessel appears over the horizon.
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Old 29-10-2013, 09:01   #127
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Re: New Inexpensive Ais Transponder

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My point that you seem to not understand is you cant use AIS for collision avoidance in the real world as it
Ships do legally. And are legally bpund to have it on board and be using it at all times.

So sorry to blow your cover Powerabout but you are not correct at all.


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Old 29-10-2013, 09:42   #128
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Re: New Inexpensive Ais Transponder

yes they do have it and its meant to be on but if you read the rules the Captain can turn it off for security reasons and it does say 'in the future it may be used as collision avoidance' which clearly means for a commercial vessel its not now.
Is the captain allowed to turn his radar off NO
Would I use it on a yacht yes for sure its a great tool and I do
That issue with ground speed versus water speed is why it cant be used as THE tool, not to mention you are now making decisions based on data generated on the other vessel etc etc, (read the IMO document) but it might well have information that can help you though.
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Old 29-10-2013, 09:46   #129
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Re: New Inexpensive Ais Transponder

So help me understand: ground speed and direction are the only relevant things in collision avoidance aren't they? How do you get speed through water using radar or even your eyes?

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Old 29-10-2013, 10:15   #130
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Re: New Inexpensive Ais Transponder

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So help me understand: ground speed and direction are the only relevant things in collision avoidance aren't they? How do you get speed through water using radar or even your eyes?

Mark
Assuming that you and the other vessel are in the same current:

You know your speed through the water, your heading (add leeway to be precise), and your SOG/COG. You can then calculate the speed and direction of the current.

Then you use the radar to measure the bearing and the rate of change in the range to the other vessel. This gives you the other vessel's course and speed relative to you.

You then subtract out the calculated current factors and your own course and speed to get the other vessels speed through the water.

These calculations could in theory all be done within your chartplotter/radar, if it had access to all this data. I doubt if any chartplotters do this though. The cases where this would matter in the collision avoidance process have to be pretty rare.
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Old 29-10-2013, 10:16   #131
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Re: New Inexpensive Ais Transponder

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So help me understand: ground speed and direction are the only relevant things in collision avoidance aren't they? How do you get speed through water using radar or even your eyes?

Mark
NO but without that data you dont get the correct vessel aspect
CPA will be the same.

There is a merchant captain in my office right now I just asked, would you call AIS a collision avoidance tool, he answer well...maybe but not really as its ground speed based and how do you know the data is correct from the other vessel., but very useful to get the other vessels name

How about we settle that its a collision avoidance tool for a yacht but not THE tool for a commercial vessel as the IMO says.
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Old 29-10-2013, 10:18   #132
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Re: New Inexpensive Ais Transponder

OK, thanks. But I am still hung up on how the other vessels STW matters to me (or anyone else using AIS). With AIS COG/SOG, I know its CPA and TCPA and whether I should make course adjustments to avoid. It doesn't seem the other vessel's actual STW matters here.

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Old 29-10-2013, 10:26   #133
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Re: New Inexpensive Ais Transponder

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So help me understand: ground speed and direction are the only relevant things in collision avoidance aren't they? How do you get speed through water using radar or even your eyes?

Mark
Commercial vessels that have ARPA mandated must have the log connected to the Radar. ARPA wont work without the log
The reason is the col regs are based on the movement of vessels in the water not over the ground
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Old 29-10-2013, 10:32   #134
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Re: New Inexpensive Ais Transponder

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My point that you seem to not understand is you cant use AIS for collision avoidance in the real world as it doesn't give you the information you actually need to apply the rules.
AIS was never intended to be a tool for that ( hence the name)but for a vessel without radar you certainly get information you didnt have before.
You are trying to wish AIS is something it is not
The implementation on commercial vessels can be a 3 line display, who's going to be reading that when on watch
AIS was implemented to allow ports to identify ships
incorrect, AIS provides information that can and is used in collision avoidance. It is not in itself a collision avoidance tool, partially because it is not ubiquitous , though teh IMO "intend" AIS to be such a tool in the future

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Old 29-10-2013, 10:34   #135
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Re: New Inexpensive Ais Transponder

as I have said before AIS is a great tool for a yacht to give information to ensure it wont hit a another vessel
Now place 4/5 300m tankers in current in a crossing TSS like the Thames estuary where you have to work out who is overtaking and who and I giving am way to, I need to know the track through the water relative to mine, not its heading, does the 3 lines of text on the AIS give me that??
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