*THE HULL TRUTH is the world's largest FREE network for the discussion of Boating & Fishing. Whether you're researching a new boat, or are a seasoned Captain, you'll find The Hull Truth Boating & Fishing Message Forum contains a wealth of information from Boaters and Sportfishermen around the world.
Welcome to the updated THT!
If you are having trouble signing in, please email feedback@thehulltruth.com with your username and we will help you. We thank you for your patience as we help you access the new site!
Random Quote: Just a thought. I never said it was a good thought.
Three things on that front:
I don't expect anyone to alter course for me (other than similar sized boats); I was merely pointing out what it shows me and how I can avoid big ships that might run me down.
AIS class A (big ships transmit at 25W of power, just like a VHF, Class B is only 2 Watts, which gives no more than about 6-8 miles in range) units allow the filtering out of Class B signals, and most every big ship does that.
As far as clutter goes, even with a class B unit, you can limit the number of targets to the closest 5, 10, 20 or 100 (at least with Garmin).
So a receive only unit would seem to be all that's needed for a recreational boat. Agreed?
So a receive only unit would seem to be all that's needed for a recreational boat. Agreed?
depends. for me, i would like to know that a big ship can see me, pretty much no matter what. so xmit is important. but i consider this a last line of defense safety equipment, so the price point isn't there yet for me.
and if you really want to get into it, just imagine what is going to happen when DHS requires all boats in certain areas to have transponders
No AIS A unit can be set to block AIS B transmissions. Some of the earliest units need a firmware upgrade to read the whole data pack, but they still show a raw target with course and speed. One or two PC based Nav programs offer the option of blocking AIS B in the mistaken belief that any company would allow it. Ask a lawyer; the answer is a firm no.
The Coast Guard is circulating a Notice of Proposed Rule Making (NPRM) that will require AIS (A or B) on an additional 17,000 vessels in the US, including tugs, tour boats, and a lot of others. There will be a lot of data out there soon, but:
AIS B has been available in the rest of the world for a half dozen years. Not even the most crowded traffic areas are over-saturated, even as crowded as they are. AIS is a way to deal with the clutter, not remove it. Try puzzling out a radar picture of 30 vessels under way, and compare it to a chart plotter that calculates the collision hazards for you, and can handle a large number of targets.
A rational seaman uses every tool available to navigate his vessel. A seaman that turns one off is not rational. A seaman that does not have a valuable tool is sailing blind and at the mercy of all those who can see. Or he's too poor or cheap.
All class B AIS's can be programmed to transmit or not, one way or another.
Some receive only units have been available for quite a while. They provide much the same information as the Transceivers (Class B and Class A), but the cheapest* may take 12 minutes to receive the full data block from a transceiver.
Notice I did not use the term transponder. An airplane has one of those, and it sends its data when asked. AIS Transceivers send their data all the time, but they do it nicely, by timing their transmissions to avoid talking over another sender. Its pretty technical, but it works.
An aside: who says airplane transponders and CAS stuff doesn't work? Check your facts.
As with anything else, there are a few truly screwy products out there (think NASA ) but there will also be a few people who think they are just fine.
To date, the FCC has approved only one or two AIS B units on their own, but they have given interim approval on a large number of manufacturers using the same circuit board, albeit in a few different boxes, and a range of prices. Yes, that means the identical functionality can be bought for as little as $600 or as much as $1300 depending on whose name is on the case. AIS B is already a commodity product! The only real differences are what else comes in the cardboard box (such as a VHF and a GPS antenna, or a transmit switch that lets you use your existing VHF antenna.)
The problems with setting up an AIS receiver or transceiver are the antenna configurations and the data connection. AIS data is too big for ordinary NMEA 0183 circuits: instead, it needs to move at 38,400 baud. This is a stumbling block for Raymarine (and other) Chart plotters, but there are work arounds. Garmin Chart plotters have several comm ports and each can be set at one or another speed.
NMEA 0183 has language to communicate AIS data. NMEA 2000 (N2K) did not until a couple months ago. Garmin used their own N2K words to move the data around the boat on a plug and play network, but I suspect that NMEA will publish a final set of words that fit Garmin or Garmin will update theirs, so its not a big deal breaker.
The beauty of using N2K to connect AIS, char plotter and VHF radios is sweet; Imagine this:
Your AIS passes the course, speed, size, description and details about a tug and 200 foot tow coming around the point. Your chart plotter calculates that you could hit it. You tap on the screen, your radio calls the tug (with DSC) and you and the tug captain get happy with the knowledge that you are not going to try to pass between those two radar targets! Substitute a trawler (as in real professional fisherman with a huge net out) or a dredge pipeline, or a big circle raft of sailboats, and you get the picture.
Aside from the posters who have to Pooh-Pooh anything new or more expensive than a six-pack, AIS is good mojo. It has already prevented collisions, and kept vessels from diving into shallow water. It IS a tool for Homeland Security, but I don't think many of us here are terrorists or pirates, so we shouldn't care if big brother is watching. Whether or not you want to transmit your position course and heading is still your choice, but clutter is not a problem. If I'm in the way of a working tug or other service craft, I would be glad to get a call from him and AIS B is the way that can happen.
And no, this is not just a toy for the idle rich. It is also a toy for the idle poor who want to stay out of trouble. That would be me. And I choose to transmit my data at night, in rain or other inclement weather, when off shore, and when coming into a strange area. I think of it as a really high mast head light.
* There are AIS receivers for less than $200 that have a single reception circuit that jumps back and forth between the two dedicated AIS frequencies. They miss stuff. If they use the same antenna as your VHF radio, they miss more stuff.
__________________ If it ain't broke, I haven't played with it.
My first exposure to the utility value of AIS occurred this last summer doing a sailboat delivery from Seattle to San Diego. Heading southbound but out far enough to catch the good wind put us in a situation similar to "going up the down staircase" with respect to the commercial vessel traffic. Visibility was sketchy even during the day and seeing those ships pop up on the laptop screen complete with boat name, heading and speed data along with the collision avoidance algorithms built into the nav software on the 'puter made standing watch in that shooting gallery far less stressful and made for far fewer course adjustments than having only radar would allow. Our unit was receive only which was OK but on the occasions when we would make radio contact with specific ships to determine if they were aware that we were close by when we noticed them making threatening course adjustments they invariably said no, they were not picking us up on radar and that we ought to be transmitting our position via AIS, not just receiving theirs. Bottom line, a freighter that knows you are there will make an effort to avoid you, in the open ocean at least, so if you're going to add AIS to your boat spend a few extra bucks and get a transceiver.
I dunno, I don't see how something that makes your vessel more visible to surrounding traffic is useless. But then, part of my working life is spent on a small 15 ton ship doing weird stuff in ferry lanes during the middle of the night. Vessel Traffic Services knows us well. I like being seen.
I agree about the problem of over-relying on electronics. Twice during the last two years I've had to dodge large yachts with no one on the bridge, presumably navigating on way points and autopilots. Our radar's ARPA is a bit flaky; it would be nice to have a bit more warning about what the nearby idiots are up to.
A quick call on the VHF is sometimes needed to clarify intentions. Having the opposing vessel's name would just be one less link in an error chain when you're trying to figure out what's going on: "Anonymous black blob in the middle of the channel just south of Surge Point, this is...". Meanwhile Anonymous Blob hasn't been paying attention to his position and is asking himself "Where the hell is Surge Point?"
No Gerg. I support them. My Garmin habit has probably put one or two of their kids through college. But I like ACR and Standard Horizon too. Then there's Airmar/Gemco, and Interphase, and, and, .....
__________________ If it ain't broke, I haven't played with it.
I didn't say they were useless. I just said they don't rise to the level of something I see a need to get for my boat.
We have lots of choices in electronics and safety gear, but only so much money. I''d love one, but I'd also love a FLIR, and about $40k of other things. But, santa is frowning, so I need to watch the budet for a while.
Personally, I'm waiting for the new crop of AIS enabled vhf radios comes out with nm2k support. The technology is just emerging. There is time to wait and watch.
__________________
Terry Jason 35, Yanmar 370 hp, Lots of fun at a leisurely pace
. . . here ya go gerg. Doesn't have NMEA2000 output but its a full function VHF & AIS receiver w/ship display & nav info. I like the mmsi direct call button. Does output the data via 0183 to your compatible plotter if needed.
