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Old 08-02-2012, 13:01   #1
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AIS Receive only or Transponder ?

Greetings: I'm adding AIS and a new chart plotter to my 40' sailboat. I'd like an AIS display unit at the chart table, outputting to the new chart plotter in the cockpit. Cruising grounds, for now, are California and Mexico; lots of shipping lanes, etc. What's the collective wisdom on spending the extra money to get a transponder unit such as the Vesper WatchMate 850? Will it add a sufficient amount of safety to justify the higher (around $600 U.S.) cost?
Thanks for your input, and fair winds!
Richard
Santa Barbara, CA
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Old 08-02-2012, 13:11   #2
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Re: AIS receive only or transponder?

Doesn't seem much point in a transponder if the Type A users are filtering out Type B. Better have a AIS Rx and Radar Guard and get on the VHF it a larger vessel is going to come to close...I would also make a course correction to get out of it's way....
My AIS is integrated with my Raymarine chart plotter, a E80 and will warn if I am on a close approach. Im about to install a loud alarm on the system that will wake me if I doze off when single handing.
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Old 08-02-2012, 13:20   #3
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Re: AIS receive only or transponder?

I wasn't sold on AIS until off the coast of Charleston at night. Even though the chart plotter conveniently stopped working so I could not see other vessels' AIS data, we were still transmitting. I watched a large container ship that was on a converging course turn 30 degrees to pass us well astern. After well clear, the ship resumed its original course. While we saw the well lit ship, it is unlikely that they ever saw our 42 foot sloop at that distance. Their actions were almost certainly a result of our AIS signal.
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Old 08-02-2012, 13:27   #4
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Re: AIS receive only or transponder?

There is at least one recent thread that already exists on this topic, so you might want to search around.

Personally, I think the receive-only units are a bad idea for a cruising boat. When out cruising it is not difficult for a cruising boat to detect a ship at a safe range, either visually (day or night) or with radar. AIS reception extends this range, and allows for an automated alarm, but doesn't dramatically change things. OTOH ships find it very difficult to detect small boats. White sails and hulls don't stand out against an ocean; the short range of our nav lights means they can't see us at night until very close if at all; and our radar cross-section is small and often lost in the sea clutter. AIS changes that: we reliably show up on their displays far enough off that minor course corrections easily avoid close approaches. And that has been my experience: shipping doesn't get close to me anymore. Sometimes they send a message via AIS or call on the DSC VHF just to check up on me. Wonderful.

I bought the Simrad AI50, 3 years ago before the last Atlantic crossing. I have been very pleased with it, and like having a dedicated (color) display. I can recommend it, but haven't looked at the market for other options.
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Old 08-02-2012, 13:28   #5
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Re: AIS receive only or transponder?

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Originally Posted by Gary H View Post
I wasn't sold on AIS until off the coast of Charleston at night. Even though the chart plotter conveniently stopped working so I could not see other vessels' AIS data, we were still transmitting. I watched a large container ship that was on a converging course turn 30 degrees to pass us well astern. After well clear, the ship resumed its original course. While we saw the well lit ship, it is unlikely that they ever saw our 42 foot sloop at that distance. Their actions were almost certainly a result of our AIS signal.
How do you know they didn't "see " you on radar? Or maybe someone on watch spotted your nav lights? The watch might well have a pair of bins or even night vision scope. Either way I would have hailed the ship in question and said thanks.
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Old 08-02-2012, 13:33   #6
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Re: AIS receive only or transponder?

I see that another poster typing at the same time has repeated the meme that commercial ships can turn off the Class B signal reception. That has been debunked a long time ago.
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Old 08-02-2012, 13:34   #7
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Re: AIS receive only or transponder?

I suppose it could have been radar, but given the distance, I doubt it was visual. I guess I'll never know for sure it was AIS since they did not respond on VHF.
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Old 08-02-2012, 13:47   #8
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Re: AIS receive only or transponder?

Anyone interested should read this page right down to the end.
Panbo: The Marine Electronics Weblog: The Class B AIS filtering myth revisited, arrrrrgh!
Of course if you can easily afford a AIS transponder then you should fit one, but once again don't assume just because you have one that the large box ship can see you more than a few miles away and that they can and will make a course change.
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Old 08-02-2012, 14:51   #9
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Re: AIS receive only or transponder?

I think it is worth the additional safety. Not only do you light up on their screen, the name of your vessel is on their screen. This makes making passing arrangements by radio much easier. There is no doubt who is who, where you are and your course and speed.

Without an AIS transceiver (assuming you are not seen) you are trying to make a boat that is twice, three or four times slower try to avoid a faster moving vessel. This is much like an armadillo trying to safely cross a freeway. It's much more effective for the truck than the armadillo to change its direction.
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Old 08-02-2012, 15:18   #10
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Re: AIS receive only or transponder?

Quote:
Originally Posted by Gruntled View Post
Greetings: I'm adding AIS and a new chart plotter to my 40' sailboat. I'd like an AIS display unit at the chart table, outputting to the new chart plotter in the cockpit. Cruising grounds, for now, are California and Mexico; lots of shipping lanes, etc. What's the collective wisdom on spending the extra money to get a transponder unit such as the Vesper WatchMate 850? Will it add a sufficient amount of safety to justify the higher (around $600 U.S.) cost?
Thanks for your input, and fair winds!
Richard
Santa Barbara, CA
If you don't need the internal AIS display, look at the network units. Prices for transceivers are getting pretty attractive.

Digital Yacht AIT2000 Transponder

or

EM TRAK MARINE ELECTRONICS B100 AIS Class B Transceiver at West Marine
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Old 08-02-2012, 15:36   #11
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Re: AIS receive only or transponder?

Quote:
Originally Posted by CarinaPDX View Post
Personally, I think the receive-only units are a bad idea for a cruising boat. When out cruising it is not difficult for a cruising boat to detect a ship at a safe range, either visually (day or night) or with radar. AIS reception extends this range, and allows for an automated alarm, but doesn't dramatically change things. OTOH ships find it very difficult to detect small boats. White sails and hulls don't stand out against an ocean; the short range of our nav lights means they can't see us at night until very close if at all; and our radar cross-section is small and often lost in the sea clutter. AIS changes that: we reliably show up on their displays far enough off that minor course corrections easily avoid close approaches.
While it is not difficult to visually detect ships at night, it is difficult to tell exactly what course they are on, their speed, and how close they will approach you. Radar, of course, helps solve this, but does not provide the one-time, easy, rapid, single glance information dump that AIS does.

Receiving AIS signals alerts you to a dangerous crossing situation with a lot of time to make small adjustments to your course to avoid danger. And anyone who is safety conscious and considerate will adjust their course rather than make a large freighter do so. If you are burdened, the received AIS signal gives you the information to actively call the ship, explain your position and negotiate a passing.

So receive only units are not a bad idea for cruising boats - they just require an approach that is avoidance-oriented and not one of "see me and get out of my way".

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Old 08-02-2012, 15:40   #12
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Re: AIS receive only or transponder?

Quote:
Originally Posted by DotDun View Post
If you don't need the internal AIS display, look at the network units. Prices for transceivers are getting pretty attractive.

Digital Yacht AIT2000 Transponder

or

EM TRAK MARINE ELECTRONICS B100 AIS Class B Transceiver at West Marine
They are coming down, but there is still a 3X differential in price between them and receive only units. So in the PO's case, this brings his $600 differential down to $400.

The difference between a $200 receive unit and a $600 transceiver can mean the difference between any AIS capability and none for some.

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Old 08-02-2012, 15:46   #13
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Re: AIS receive only or transponder?

Quote:
Originally Posted by Gruntled View Post
Greetings: I'm adding AIS and a new chart plotter to my 40' sailboat. I'd like an AIS display unit at the chart table, outputting to the new chart plotter in the cockpit. Cruising grounds, for now, are California and Mexico; lots of shipping lanes, etc. What's the collective wisdom on spending the extra money to get a transponder unit such as the Vesper WatchMate 850? Will it add a sufficient amount of safety to justify the higher (around $600 U.S.) cost?
Thanks for your input, and fair winds!
Richard
Santa Barbara, CA
If you have a fixed amount to spend, and it is enough to buy a transponder, but only one like DotDun mentions, and not one with a second display for the chart table, then get the transponder. I don't see the real need for one at the chart table. AIS provides such a range that you can set up alarm zones that will give you lots of time to look at the chartplotter and plan a course of action.

Can your chartplotter be networked to another display below? Either an inexpensive computer monitor or a wifi connection to a iPod touch, etc? If so, I would go with a transponder and mirror the chartplotter display below if you still feel that is necessary.

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Old 08-02-2012, 16:00   #14
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Re: AIS receive only or transponder?

I solo crossed the Atlantic twice and did alot of bluewater sailing with only an RX AIS (NASA) cheap, reliable.
I feel that I am always the underdog, so it is my responsibility to take action. When a large ship is on collision course you just call them by their ships name on VHF. So far always positive reactions and they always change their course and thank me for calling.

The only comment on the NASA is that when a vessel enters your alarm area, you have to shut off the audible alarm and you can only switch this on again when no ships are in your area.
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Old 08-02-2012, 16:44   #15
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Re: AIS receive only or transponder?

Outstandingly helpful responses, and on the same day! Thanks very much.
Richard
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