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Old 23-01-2013, 17:56   #31
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Re: New Inexpensive Ais Transponder

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Originally Posted by skipmac View Post
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.
The advantage is that the AIS will identify speed, course and name of the vessel in question. If you are in harbour approaches or restricted waters, you can call their bridge BY NAME, inform them you are close, and thereby avoid being surprised by any course changes they may be contemplating.

Stories circulate of commercial vessels "seeing" small FG yachts on AIS that never paint on their radars, either for reflectivity reasons, height of swell or other technical shortcomings. Being seen can be equally useful, in my view.

They also make decent anchor watch devices.
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Old 23-01-2013, 18:08   #32
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Re: New Inexpensive Ais Transponder

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So I just don't see the difficulty in avoiding a collision with a big ship.
It's not that hard, true.

With a receiver costing less than a mid range wet weather jacket and drawing 0.1A it's even easier, 5 miles away and you can usually relax knowing there will be plenty sea room. What's not to like?
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Old 23-01-2013, 18:40   #33
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Re: New Inexpensive Ais Transponder

skipmac - from the tone of this thread i think you and i are the only sailors left who are actually looking out the 'window'. everybody else is glued to the ais screen, chart plotter, radar plot, and forward scanning sonar.

back in the day we had to actually hand plot our way across. which is probably why there was so much less yacht traffic then. i never sleep, or even go down below to relieve myself, during the crossing. always scanning the horizon, taking bearings on every light i see. never got closer than a mile to a freighter.

the only reason i enquired about an ais is that i want to give the big guys a better look at me. i don't need an ais to see them.
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Old 23-01-2013, 19:28   #34
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Re: new inexpensive ais transponder

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Originally Posted by jeremiason View Post
AIS is VHF radio, meaning in theory, it is line of sight... Class B transmits at 2 Watts and Class transmits at 12 watts.

I have a AIS Class B on my boat with a masthead antenna and normally am seen at between 8-12 miles on calm waters... The transmission distance is reduced significantly if the boat is rolling hard... Something to do with the antenna lobe radiation at sever angels, if I remember right...

Anyway, for your requirements, you will need a proper Class B AIS unit for power and an antenna mounted as high as you can get it.
I do not believe this is completely accurate.

In few words, AIS is a technology that can send and receive static data (identifying the boat) and dynamic data (coming from a GPS) over two VHF channels in a coverage radio that can reach up to 60NM in optimal conditions, although the usual coverage reaches 30NM. An AIS transponder needs then to be connected to a VHF antenna and a GPS one too. The GPS antenna can be the one already on board, although the VHF one must be a dedicated one, since AIS emissions and VHF voice working with the same antenna is uncompatible. We have a splitter solutions for AIS reception though.

Ken
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Old 23-01-2013, 20:02   #35
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Re: New Inexpensive Ais Transponder

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Originally Posted by conachair View Post
It's not that hard, true.

With a receiver costing less than a mid range wet weather jacket and drawing 0.1A it's even easier, 5 miles away and you can usually relax knowing there will be plenty sea room. What's not to like?
Oh it's not that I don't like them and I'm sure they do what they say they will do. Just never had any trouble at all not seeing or running into a 500' boat. I even do pretty well with smaller than that though my vision isn't what it used to be.

Another point made on another thread about AIS, not every boat has it. Plenty of smaller boats like fishing trawlers and such that aren't required to use AIS but still big enough to ruin your day if you collide. So for low viz situations I think radar a better tool.

Also at some point where do you reach information overload and your trying to digest information from mulitiple inputs or even multiple displays? Which also brings up the cost factor. To avoid having multiple screens and displays to watch to keep track of: course, speed, depth, radar, chart, AIS, AP, etc you need to get a multi function display and integrate all the many inputs. This can start adding up to big money, at least what I would call big in my book. Then even with one MFD you may have to spend a bit of time messing with menus, zoom, programming what data to show.

I think I would just rather look around at what's coming and going.

Just in case I am mistaken for an antiquated old fart or even so kind of Luddite, I degreed in electrical engineering and bought my first computer in 1980 and generally love gadgets.
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Old 23-01-2013, 20:09   #36
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Re: New Inexpensive Ais Transponder

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Originally Posted by onestepcsy37 View Post
skipmac - from the tone of this thread i think you and i are the only sailors left who are actually looking out the 'window'. everybody else is glued to the ais screen, chart plotter, radar plot, and forward scanning sonar.

back in the day we had to actually hand plot our way across. which is probably why there was so much less yacht traffic then. i never sleep, or even go down below to relieve myself, during the crossing. always scanning the horizon, taking bearings on every light i see. never got closer than a mile to a freighter.

the only reason i enquired about an ais is that i want to give the big guys a better look at me. i don't need an ais to see them.
I did get closer than a mile twice. Once because the guy on watch (I won't mention any names) didn't think to turn around and look behind us. I happened to come on deck and saw a giant freighter about 1/4 mile behind and overtaking. The second time I was on watch and was a bit tired and didn't go aft to look behind the genoa for a while (center cockpit boat so healed over the gennie blocked a large area). Finally occurred to me that a look see was overdue and I discovered the Exumas mailboat was about 1/4 mile to port. Hello!

One thing that I would like from AIS is to know the name of the boats around you. I tight quarters or bad viz I'll call other boats but always something like "sailboat calling tug pushing barges westbound." It would be very cool to call them by name.
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Old 23-01-2013, 20:16   #37
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Re: New Inexpensive Ais Transponder

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Originally Posted by S/V Alchemy View Post
The advantage is that the AIS will identify speed, course and name of the vessel in question. If you are in harbour approaches or restricted waters, you can call their bridge BY NAME, inform them you are close,
Knowing the name would be very handy. But so far I have managed to stay far enough away from the big boats that any changes they make in course or speed have not been a concern.

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Originally Posted by S/V Alchemy View Post
Stories circulate of commercial vessels "seeing" small FG yachts on AIS that never paint on their radars, either for reflectivity reasons, height of swell or other technical shortcomings. Being seen can be equally useful, in my view.
I spoke a number of big ships back when I was doing a lot of offshore work and they generally said, except in very mild conditions, they could see me or my lights better that radar image if they got me on radar at all.

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They also make decent anchor watch devices.
I'm not familiar with that feature. In the context of warning of the presence of another boat passing or does it alarm if your boat moves position?
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Old 24-01-2013, 03:40   #38
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Re: new inexpensive ais transponder

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Originally Posted by missnmountains View Post
In few words, AIS is a technology that can send and receive static data (identifying the boat) and dynamic data (coming from a GPS) over two VHF channels in a coverage radio that can reach up to 60NM in optimal conditions, although the usual coverage reaches 30NM.
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You are correct that AIS Class A will transmit 30-60 miles, DEPENDING on the height of both the transmitting and receiving antennas, but Class B will only transmit about 8-12 miles, again depending on the height of the Antennas...

It is a matter of transmission power: Class A-12 Watts, Class B-2 Watts

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The GPS antenna can be the one already on board, although the VHF one must be a dedicated one, since AIS emissions and VHF voice working with the same antenna is incompatible. We have splitter solutions for AIS reception though.
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WRONG! By USCG and IMO regulations, a Marine AIS transponder, Class A or B is required to have its own stand alone GPS Antenna.

As for the VHF antenna, many Class B units are built with splitters to share your mastheaad antenna, which works just fine...

For all you ever wanted to know about AIS, here is a link to the USCG AIS Page
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Old 24-01-2013, 05:15   #39
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Re: New Inexpensive Ais Transponder

I think we're pretty close in approach to sailing but a few points in red below which may or may not be of interest to anyone considering getting a receiver..

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Originally Posted by skipmac View Post
Oh it's not that I don't like them and I'm sure they do what they say they will do. Just never had any trouble at all not seeing or running into a 500' boat. I even do pretty well with smaller than that though my vision isn't what it used to be.

Me neither, , it just really nice to know the exact course and speed of a big boat when it's still 5 miles away, no need to take bearings or fire up the radar.


Another point made on another thread about AIS, not every boat has it. Plenty of smaller boats like fishing trawlers and such that aren't required to use AIS but still big enough to ruin your day if you collide. So for low viz situations I think radar a better tool.
True, but with the smaller boats I've found that any info on speed and course isn't really much use anyway, you really need to keep an eye on them they can change course and speed at a moments notice but at least they are usually quite easy to dodge at close quarters. Occasionally if a fishing boat is transmitting it can be handy to see by the low speed that it has nets down. Radar & AIS i find work really well together in low viz, radar would come first in that situation though.


Also at some point where do you reach information overload and your trying to digest information from mulitiple inputs or even multiple displays? Which also brings up the cost factor. To avoid having multiple screens and displays to watch to keep track of: course, speed, depth, radar, chart, AIS, AP, etc you need to get a multi function display and integrate all the many inputs. This can start adding up to big money, at least what I would call big in my book. Then even with one MFD you may have to spend a bit of time messing with menus, zoom, programming what data to show.

Wouldn't know Most of the time i have just paper chart, depth/speed and ais on. Laptop with chartplotter if it helps. Radar hardly ever, too power hungry

I think I would just rather look around at what's coming and going.
Me too Nearly all the time. But having a little friend down below dishing out loads of useful info can make life very easy now and again

Just in case I am mistaken for an antiquated old fart or even so kind of Luddite, I degreed in electrical engineering and bought my first computer in 1980 and generally love gadgets.

Slight drift but I'm a bit wary of linking them all together, prefer a solid backbone of a few standalones so if one goes down you don't loose the lot
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Old 24-01-2013, 05:43   #40
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I too think AIS is relatively useless. However a few days ago while being slowly overtaken by a large cargo ship I used the AIS and OpenCPN to advantage. It was advantageous if I could cross his bow but in the rough fast conditions I found it difficult to estimate the safety of such a bold move. The OpenCPN plot said "Go for it!" It would have been pathetic to slow this girl down and take the indignity of his stern. Heh.

And I figured he had probably computed my crossing as well and would consider me a fool to not take his bow. Eat my wake suckkkah!
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Old 24-01-2013, 05:50   #41
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Quote:
Originally Posted by onestepcsy37 View Post
i came across this ais transponder today. it's advertised as the lowest cost transponder and also self contained with it's own battery and antenna. couldn't find a price for it.

AIS Identifier

sounds like it's just what i want. i only need an ais to cross the gulf stream at night - florida to bahamas. i just want to be visible to other ships, don't really need or want to track them. so i'm looking for something that's self contained and inexpensive. this one seems to fit.

i know dirt about ais so i'm asking the electronics experts out there to tell me what they think of it, given my requirements. my concern is that it seems to work only on certain 'channels' and i don't know if these are the 'channels' that regular ais works on, so will i be visible to ships if i use this device?

all ais people please advise....
Why crossing the Gulf Stream at night, in the first place?
Any special reason?
Doesn't seem to me as a smart move.
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Old 24-01-2013, 07:34   #42
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Re: New Inexpensive Ais Transponder

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I'm not familiar with that feature. In the context of warning of the presence of another boat passing or does it alarm if your boat moves position?
I think you could do it that way, but I believe the usual method is that you set the distance from the anchor "drop point" in terms of the radius of a circle. Drift beyond that circle and the alarm goes off, meaning that the AIS is relying upon its "background" function as a GPS.

There's a brief video here:



If you had a fixed AIS target, like a docked tanker and your boat was dead downwind from said fixed point, you could calculate what distance would suggest a drag, and then just set the alarm for a few meters beyond that point, depending on what was directly aft of your stern.
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Old 24-01-2013, 07:42   #43
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Re: New Inexpensive Ais Transponder

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Why crossing the Gulf Stream at night, in the first place?
Any special reason?
Doesn't seem to me as a smart move.
In a slow sailboat a night crossing allows a daylight landfall in the Bahamas. Don't want to arrive too early as the morning sun will be in your eyes and reflecting off the water ahead so visual navigation into a channel or onto the banks tricky.

Also, back in the olden days before GPS you could pick up the lights on the radio towers at Bimini or West End from miles away and more accurately adjust course to compensate for the northerly set of the Gulf Stream.

Also arriving late morning in the Bahamas puts you there during business hours so you can clear customs with much less hassle.
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Old 24-01-2013, 07:46   #44
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Re: New Inexpensive Ais Transponder

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Originally Posted by S/V Alchemy View Post
I think you could do it that way, but I believe the usual method is that you set the distance from the anchor "drop point" in terms of the radius of a circle. Drift beyond that circle and the alarm goes off, meaning that the AIS is relying upon its "background" function as a GPS.
Interesting. Is this a feature of all AIS units or just this one? Obviously I have not yet invested much time in checking out AIS systems.

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If you had a fixed AIS target, like a docked tanker and your boat was dead downwind from said fixed point, you could calculate what distance would suggest a drag, and then just set the alarm for a few meters beyond that point, depending on what was directly aft of your stern.
Unless the tanker decided to steam away in the middle of the night.
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Old 24-01-2013, 11:40   #45
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Re: New Inexpensive Ais Transponder

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In a slow sailboat a night crossing allows a daylight landfall in the Bahamas.
Even most of the power boat guys that I know prefer to leave before sunrise, so that the light is right when they are navigating the many shoals and reefs of the Bahamas.
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