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Old 23-01-2013, 07:04   #16
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Re: new inexpensive ais transponder

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Tim

I was driving commercial boats in San Francisco and never had the need to filter out Class B targets, but I could see the need in parades or opening day ceremonies as an example...

I would imagine as Class B becomes more popular that in areas where there is high vessel traffic, it may happen in order to avoid the collision alarm from going off frequently. But not once you on the open ocean.

But both International and US Rules require the Captain to use all available means for lookout, which has been interpreted to include Radar and AIS.

God help the first Captain who strikes a Class B AIS Target, because he was filtering and therefore not providing a proper look out under both International and US Law.
Agreed Tom but collisions have happened from improper visual lookout so I would think it could happen with AIS. That is why I will try to control my safety as much as possible by keeping a proper watch and using my RADAR, AIS, VHF and any other means available to find and communicate with other vessels that may be out there.
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Old 23-01-2013, 07:10   #17
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Re: New Inexpensive Ais Transponder

Yet another totally pointless "discussion"!!!
It is irrelevant whether they are looking for you on AIS. YOU are responsible for YOUR safety and YOUR vessel!! No discussion.
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Old 23-01-2013, 07:24   #18
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Re: New Inexpensive Ais Transponder

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all ais people please advise....
Apart from all the other concerns, wouldn't that unit play havoc with a receiver on the same boat?

If the choice came down to transmit only or receive only then I would go for receive every time.
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Old 23-01-2013, 07:33   #19
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Re: New Inexpensive Ais Transponder

Here is a link to another "transmit only" AIS device, that can deliver 2 or 8 watts: https://www.google.com/url?sa=t&rct=...41248874,d.cGE

The product description does suggest installing such devices on manned vessels. I recall earlier discussion of such products being developed for unmanned hazards such as buoys, rocks, or anchored barges. They are not legal for use on vessels required to have AIS.
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Old 23-01-2013, 07:54   #20
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Re: new inexpensive ais transponder

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Originally Posted by Tim R. View Post
...That is why I will try to control my safety as much as possible by keeping a proper watch and using my RADAR, AIS, VHF and any other means available to find and communicate with other vessels that may be out there.
Agree. But, AIS technology allows to see and be seen. Since collision avoidance is a multiplayer adventure, it's prudent to value AIS transmit and receive equally.

Plus, all must remember that AIS is missing from 90%+ of vessels on the water, hence use of all available tools plus a proper watch is required.
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Old 23-01-2013, 08:28   #21
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Re: new inexpensive ais transponder

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Agree. But, AIS technology allows to see and be seen. Since collision avoidance is a multiplayer adventure, it's prudent to value AIS transmit and receive equally.

Plus, all must remember that AIS is missing from 90%+ of vessels on the water, hence use of all available tools plus a proper watch is required.
That is why I use a transceiver. Transmit and receive. Give me a choice and I will take receive over transmit every day of the week.
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Old 23-01-2013, 08:31   #22
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Re: new inexpensive ais transponder

I am pretty sure I read something on Panbo the refuted the notion that commercial ships filtered out Class b signals. What I took away was that tis is internet generated false information. Do you have evidence that what you say is true?

It should be noted that most fishing vessels you will see off the the east coast of the US (and I imagine elsewhere) are not transmitting AIS, and are also not standing a watch to see your transmission.

Chris

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Your first statement here is a very dangerous one. Many commercial ships will filter out Class B signals and they will not see you. They are required to transmit a class A signal that you can and will see. You will be much safer going with a receiver and standing a proper watch.

Receivers are cheap now. If your VHF needs updating you can get one that has VHF for about $200 or less if you shop around.

Do not put your safety in someone else's hands.
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Old 23-01-2013, 08:49   #23
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Re: new inexpensive ais transponder

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I am pretty sure I read something on Panbo the refuted the notion that commercial ships filtered out Class b signals. What I took away was that tis is internet generated false information. Do you have evidence that what you say is true?

It should be noted that most fishing vessels you will see off the the east coast of the US (and I imagine elsewhere) are not transmitting AIS, and are also not standing a watch to see your transmission.

Chris
No evidence. Just the word of a commercial captain with 15 years on the sea.

I realize not every boat has AIS. That is why I also use my eyes and my RADAR.
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Old 23-01-2013, 10:09   #24
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Re: new inexpensive ais transponder

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Many commercial ships will filter out Class B signals and they will not see you.
At best, this is a persistent internet myth. Such filtering would be grounds for a finding of negligence in any case where Class B signals were filtered out prior to a collision.
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Old 23-01-2013, 10:11   #25
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Re: new inexpensive ais transponder

Regarding the debate on whether or not AIS-A vessels monitor AIS-B signals, it is worth considering that none of the early AIS-A equipment was capable of receiving AIS-B signals. I do not know if there is any requirement that such equipment be upgraded. We do know that the AIS-A equipment can de-select the display of AIS-B targets.

In any case, prudent mariners must assume that crossing vessels are not aware of your position, course, and intention unless verified via VHF contact.
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Old 23-01-2013, 10:15   #26
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Re: New Inexpensive Ais Transponder

Here's a link to a similar unit from Em-trak em-trak - em-trak I100

I see the value in these as being something you mount in a life raft or dinghy when abandoning ship. Or maybe even finding the kids when they haven't returned to the anchorage from a day of exploring on their own.

Bruce
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Old 23-01-2013, 10:24   #27
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Re: New Inexpensive Ais Transponder

Not saying AIS is a bad thing but for me I just don't see it as that useful and certainly not necessary. I've crossed the Gulf Stream numerous times, crossed other very busy shipping channels, sailed across NY harbor with ships going in all directions and never had any problem staying out of the way of a big ship.

Unless you're in dense fog you can see a big ship 5-10 miles or more. Once they get within a mile or two their course and approximate speed should be very easy to determine with just the naked eye.

I did a rough calculation and estimate if you literally fell asleep at the wheel and woke up to find your boat dead ahead of a giant freighter, even if you are only making 4-5 kts and had to cross all the way across the bow of the oncoming freighter it would take maybe 20-30 seconds max. I think one would have to screw up very, very badly to put a boat in a situation where there was less than 20-30 seconds to avoid a collision.

So I just don't see the difficulty in avoiding a collision with a big ship. In 35 years of sailing, twice I was on a boat that came within 1/4 mile of a freighter and both times were due to the crew on watch falling asleep or otherwise not paying attention. Don't think AIS would have helped in either case unless the unit can be configured to sound off a loud alarm but then I know I could do that with radar.
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Old 23-01-2013, 10:25   #28
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Re: new inexpensive ais transponder

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No evidence. Just the word of a commercial captain with 15 years on the sea.

I realize not every boat has AIS. That is why I also use my eyes and my RADAR.
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Old 23-01-2013, 17:31   #29
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Re: New Inexpensive Ais Transponder

In practice I have never seen Class B AIS transponders filtered, but the reasons one might want to do so, and the reason why this is a designed option, is obvious. Normally in inshore waters an AIS unit on a ship is showing maybe a couple dozen other AIS contacts. These appear on the ECDIS display along with plotted radar contacts and also the navigation chart features, route, waypoints, etc. Sometimes, like on holiday weekends and such when the weather is perfect for taking the boat out, if everyone were transmitting their AIS data there could be hundreds of AIS contacts to deal with. Now there could reach a point where there is simply too much stuff on the screen. Remember, you are mostly concerned with vessels that will approach you within, say, 5 boat lengths. A 700 foot ship is also concerned with more or less the same approach distance but his boat lengths are bigger than yours. On your boat you are very much concerned with anyone ahead of you who is coming within twice or thrice your stopping distance. A ship is also concerned with anything ahead within a multiple of his stopping distance, which is far, far greater. You may be quite comfortable with your radar on half mile to three mile scale... a ship under the same circumstances might have a 10cm radar on 12 mile range and a 3cm on 6 mile range, double that at sea and away from the inshore traffic. So information overload is a real possibility. The screen simply gets too cluttered. I have never yet seen the AIS put into "B filtering" mode but I can see how it might under extreme circumstances be deemed necessary and appropriate, and definitely not irresponsible.

Basically, yes, you should get the transciever, so you can be seen also, and not just see others. But more important than an AIS is a good radar reflector. Fiberglass boats don't paint as well on radar as a steel vessel does. The aluminum mast that has mostly replaced wooden ones, still is not a very big radar target. A corner reflector is easy to make, not expensive to buy ready-made, and is very effective. Plus it uses no power. It could save your life or that of your crew or guests.

Until you have been on the bridge of a ship in heavy traffic, it is pretty hard to envision being concerned with vessels that are still 6 or 7 miles away, but that is indeed the case. This is often at the limit of visibility by eye or radar for small boats from a ship's bridge. Pleasure boaters often maneuver erratically and unexpectedly, further confusing the watch on the ship. A ship being steered by hand is holding a course to within 2 or 3 tenths of a degree and making definite and obvious course changes at waypoints. A yacht being steered by hand will be all over the place, sometimes navigating by the "do it like ya feel it" style, and with no definite destination other than eventually getting back to the marina. From a ship's bridge the horizon is well over 10 miles away. We often spot other ships visually at better than 20 miles distance. That is a lot of ocean to scan. From a salboat cockpit the horizon is way way less than that. It is a whole different perspective. The sailboat can stop almost instantly. The ship can stop, with no danger of damage to the engine, in SEVERAL MILES. Even in an emergency, with a likelyhood of significant damage to an engine with pistons big enough for you and your wife to dance on, the stopping distance is hard to envision when you have never stood watch on a ship's bridge.

Yes, when not in a narrow channel, and when the ship is not constrained by draft, and you are under sail, the rules clearly state that the ship, as a motor vessel, must keep clear of you. However, a reality check might have you reconsider pushing the issue, not because he is bigger than you or that his vessel cost 60M while yours cost 60K, but because he has a lot more on his plate to deal with than you do and simply cannot maneuver like you can.

You need to see everybody else, including commercial vessels and including ships. You need to be visible to everyone else, too. The only reason for getting an AIS receiver instead of a transciever is you simply cannot afford the $300 or so difference. I say if you are gonna go for a reciever, do without something else, and get the transciever. And put up a radar reflector, please! And do try to avoid close encounters with a ship, or doing anything to confuse them as to your intentions.
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Old 23-01-2013, 17:50   #30
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Re: New Inexpensive Ais Transponder

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I agree totally with you Tim. The "be seen" function is definitely secondary to the "see" function. We opted for a receive only AIS a few years back in part because of difficulty positioning a transmitting AIS antenna away from our VHF antennas. Would not be without it. At 2am one night, we were 20 miles off Savannah in the midst of about 15 large vessels. AIS showed clearly where they were. Much clearer than radar in my opinion, though we use both together routinely. I figure it is my obligation to keep away from large ships, not the other way around!! That is not to say that I would not have added the transmit function if I could have done so without issue.
I consider AIS and RADAR to be mutually reinforcing: The RADAR shows you what things are around you, and the AIS tells you which things are probably other vessels, leaving rocks, buoys, reefs, picnic tables and awash containers to avoid, only some of which can be reasonably expected to move with tide and current.
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