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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 11-20-2007
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Ais

Has anyone any experience with AIS?
Both receive only and full transponder.
Thanks
lawrie
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Old 11-20-2007
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I haqve a receiver I bought a year ago from Seatech. It is plugged in Maxsea and also through a black box taht allows me to use my masthead VHF antenna for reception. Works great - gives names of ships, speed course, point of closest approach, etc. Of most vaue at night, has about 25 mile range (85 ft mast). Transmitters for <30 meter boats will be class B and I'm thinking that homeland security will require them for offshore passages eventually.
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Old 11-20-2007
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Just arrived in Puerto Rico after 8 days coming down from Norfolk. The new SR 161 AIS receiver came in very handy offshore. For example, one night it showed a ship coming head on about 8 miles away with a predicted CPA (closest point of approach) of 0.05 miles. It also gave the name of the ship, who responded when I called them on the VHF. They hadn't seen me yet, but agreed to pass port to port. We both altered course to starboard about 10 degrees ( I could see them make their course change on the AIS readout) and passed safely with a mile between us.

Pre AIS, it would have been more stressful for both of us, as I would have been calling them as ' northbound ship at 32-21 north by 68-07 West' (which they tend not to answer), trying to judge their CPA based on radar and range lights, and probably changing my course by 40 degrees trying to get some separation. On their part, a target well inside their rules for the CPA would finally pop up on their radar at about 5 miles out, confused with sea clutter, and my lights might not become visible until about 2-3 miles out, causing some last minute concerns and major course changes on their part.

It was also great to check the AIS as a squall was hitting--when visual and radar contacts were going to be blanked out it was very comforting to know that there were no big ships to worry about for an hour.

The SR161 draws about 0.25 amps at 12 volts, and was hooked to a laptop running the (free) SeaClear II program. The laptop draws less than 0.5 amps in sleep mode and about 2.5 amps while running, so checking the AIS every 20 minutes draws much less power than radar.

The class B AIS transponders will give ships the ability to see us at much greater ranges and a name to call on the VHF to sort out close encounters. There may be some issues in equipping all pleasure boats with AIS in busy harbors, as the screen can get cluttered with targets. However, I think that some changes in the display software would help to distinguish ships from boats. Offshore, I think everyone will be happier and safer with AIS and I plan to install a class B unit soon after they become available.
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Old 11-21-2007
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Nice endorsement, and while I will eventually install radar, I can see that AIS combined with laptop chartplotting will play a large role in my watchkeeping.
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Old 11-21-2007
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I fitted a NASA AIS "radar" (sic) which is an AIS receiver with its own screen, as I don't use a chart plotter. It has already proved its usefulness one very foggy morning and complements my radar very well.

I decided against waiting any longer for Class B transceivers to get certified, and their price to drop.

Also, apparently, the Class A transceivers will have the ability to de-clutter their screens by suppressing display of Class B transmissions, the CG will be able to tell Class B transceivers to cease or reduce transmissions, but those aren't the main problems for Class B users.

Already I can see that Class A transmissions are often wrong, as the ship's OOW does not change the data that a Class A transceiver transmits - its not all automatic. Some leave their transceivers off.

Worse, most Class A transceivers are not connected to a radar screen or ECDIS, and just have a Minimum Keyboard Display (three lines of text) which is very often not in the OOW's primary field of view, i.e. it is not being used to detect other vessels, maybe only to identify them.

So I decided a receiver, to tell me about the big guys, is more useful than a transceiver, which is trying to tell the big guys that I am there. I hope that situation will change with time.
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Old 11-21-2007
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I thought this subject had come up before..
The thing is, there is no practical reason not to buy just the receiver. The 'mandated' vessels, that is those mostly commercial and of a certain size, don't necessarily care about who you are and what you're up to unless you're a clear danger to them...not likely. A Class A system (transponder) will provide way too much information, the equivalent of 'junk mail' just when it's needed least. By it's nature, it transmits data pertinent to that vessel almost all the time. When you see legitimate AIS traffic on your screen in a major shipping lane, you'll soon wish you could differentiate those vessels that represent a clear danger to YOU from those that don't. Class B, single channel receive only, is a really nicely developed technology that works, all the time and is cheap...relatively.
Howard Keiper
Sea Quest
Berkeley
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Old 11-21-2007
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I see Panbo is flattering the SIMRAD unit.
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Old 11-21-2007
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After doing some minimal research to understand what AIS is it becomes apparent that it is a must have for recreational boaters in heavy commercial traffic areas. According to 'thekiep' the KISS principle applies aptly.
So what would be the most economical, effective and optimum configuration using the KISS principle. My current electronics setup includes a handheld Garmin GPS MAP76cs connected to a UNIDEN 525 VHF for DSC capability with a WHAM x4 option and a connection from my Garmin to the Raymarine ST400 Mark2+ Autopilot and another connection via USB to my notebook for live tracking via Garmins' n-route software. How would I integrate AIS into this setup?
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Old 11-22-2007
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You don't have a chart plotter or radar display to accept the NMEA info from an AIS unit and display it.

I had the same situation, so chose the NASA AIS radar receiver, with its own screen. It needs its own antenna and is not supposed to use a splitter to share the DSC antenna, though I suspect that would work. I tried a variety of antennas, even just borrowing the stub antenna of my hand held VHF. They all worked, obviously, the mast head one gave the best range. I ended up adding a pushpit antenna, which I can use as an emergency antenna, or, if I get a Class B unit, it will serve for that.

Raymarine and Simrad are coming out with attractive colour screen Class B units, but they are around $1500 I hear, so the $300 set up that I have is good value.
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Old 11-22-2007
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The NASA AIS "radar" looks nice. However,
I tried the cheapo approach, modifying a scanner by tapping into the discriminator output and using ShipPlotter . Never got it working before the free trial expired. Seems like a good way to go if it works using SeaClear or similar for those of us who have radar made before the displays accepted AIS data.
Any one else have luck with this?
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