AIS, Receiver or Transmitter

[barnakiel]

Originally Posted by Mike OReilly

(...)

1) ... a question here (an honest question, not a challenge): how do you decide to remain the stand-on vessel in these distant encounters in open water? Presumably you can see them on AIS just as well as they can see you. Why don't you alter course?


2) And maybe that's the answer to your question; maybe those who don't alter course just figure it is you who should alter course, not they.

1) I do alter our course when I feel the CPA suggests the ship is not taking action for whatever reason. When this is the case, I change our course and/or speed very VERY early on and I make a clear and unambiguous alteration.

You are correct to assume I can see many of them on the AIS. However, I never assume they can see us. Been on their bridge, kept watch, understand their challenges.

When in serious doubt, I will DSC the ship (our AIS makes a direct DSC call without any need for manual dialing: select the ship on the AIS screen, press the call button, wait).

2) The rules are clear in open waters and boats unrestricted: steam gives way to sail. Nothing left out to 'figure'. Neither for them, nor for me.

As a small aside: I have made a couple of dozen VHF calls to ships passing us by asking them things I am interested in (could they see us, how early, by what method, etc.). Some respond, others do not. My personal ranking goes like this:

- tugs: will see you, will VHF you, have AIS, DSC, and keep good watch,
- military: see you always, may respond to VHF, many are not transmitting,
- big cargo (MSC, Maersk, etc): may see you, will respond, great people,
- cruisers: same as big cargo,
- small cargo: often no response, often passing too close, AIS on,
- sailors: are not watching, AIS on, will talk to you,
- fishers: are not watching, AIS off, no VHF watch either.

Cheers,
b.

[Adelie]

Originally Posted by barnakiel

But hold on.

This is what I found looking up the web:

A transponder costs from USD 399.00 upwards (with display). There is also at least one unit priced at USD 320.00 (no display). Price data from Amazon. Google.

I also know nothing about USD 200 VHF radios having AIS receiver built in on a regular basis. E.g. a SH VHF/AIS RX combo costs 345 at the same source as quoted above.

So.

It is 345 vs. 399 by my web search.

This is 16% - NOT the 200% you found.

Sure, there is a difference. How much of a difference and whether this is much or little I will have to leave open to discussion.

I respect your view 100%. I think we are simply looking up different units in different shops.

Cheers,
b.

Separate units require added cabling and an antenna splitter. Splitters run $250ish and extra cabling about $50. And that presumes you can arrange display on a monitor you were going to run all the time anyway. If you are considering a VHF/AIS radio the the basis for comparison should be the the cost difference to add the AIS feature which is about $250.

So adding a TX unit is $320(unit) + $250 (splitter) + $50(cabling) = $620 assuming existing display
Vs.
$250 cost difference for RX only on VHF.

That's a 148% cost increase to get TX, more if you include display costs.

Alternative to adding a splitter you could install a separate antenna but then cabling costs increase, you need to buy and install the extra antenna. If you mount the second antenna at the masthead there will be interference between the two antennas at least on certain relative bearings and possibly all around.


A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.

[barnakiel]

Originally Posted by rwidman

I do think it's foolish though to expect the QE II to alter course for a 30' recreational boat (...)

Not according to the Colregs. Ask QE II bridge crew what they think, I bet they will alter it.

I understand your drift, Colregs written in times before mass leisure boat hysteria. Maybe a time for an edit. True.

But, as is, foolish or not, they are supposed to alter it. (And they do).

b.

[Mike OReilly]

Originally Posted by barnakiel

...You are correct to assume I can see many of them on the AIS. However, I never assume they can see us. Been on their bridge, kept watch, understand their challenges.

Thanks Barn/Dockhead, but I guess this is what I'm trying to figure out. I, like you, never assume they can see me. I take appropriate action to avoid a collision. I have a reasonable grasp of the COLREGS, and understand the need for each vessel to play its assigned part. If you're stand-on, it is vital to remain so until it is clear the give-way is not giving way. At that point there is equal responsibility to take the necessary action to avoid a collision.

But in open waters, with great distances between vessels, the notion of who is stand-on becomes rather academic. Under the assumption that they may not see me, I would take the minor corrective action required to avoid a collision that I thought was becoming possible. Unless, as you say, I was somehow restricted in my maneuvering, why wouldn't I take the minor action before it became major.

[Don C L]

Originally Posted by barnakiel

Not according to the Colregs. Ask QE II bridge crew what they think, I bet they will alter it.

I understand your drift, Colregs written in times before mass leisure boat hysteria. Maybe a time for an edit. True.

But, as is, foolish or not, they are supposed to alter it. (And they do).

b.

A lot more likely to alter course for a blip that includes speed, course, name and type of craft than a radar blip I bet. Especially when you consider that they know the smaller craft also has all the same data on them and can record it or relay it if anything done isn't according to Hoyle, no?

[barnakiel]

@ Adelie

Yep.

The price difference depends on what is already present as well as on what we elect to buy. Screens vs. no screens, splitters vs. no splitters, combo vs. stand alone. Very many variables. In some configs the difference is minimal, in others it can be hundreds and more.

Surely not everybody wants or needs a tx unit.

I think those that do want or need one, do not see the price difference as a factor. I think the difference is small for basic configs. All this said from onboard a boat that actively posted in 'sailing a USD 500 budget' stating and showing many times that it is 100% doable.

We have a rx unit now (a combo). I am buying a tx unit as soon as I can (possibly the blue box vesper as it is wifi capable and ipx7). We are sailing a very wee boat and basically only crossings. We get tired way more than strong crews in big boats. We are 'invisible' to the big ships in rough seas (offshore, in a small craft, this is basically always).

I want to believe we get as much chance of getting spotted before getting crushed as we can afford. And we surely can afford USD 500 on a piece of gear that will serve us over many years.

b.

[barnakiel]

Originally Posted by Don C L

A lot more likely to alter course for a blip that includes speed, course, name and type of craft than a radar blip I bet. Especially when you consider that they know the smaller craft also has all the same data on them and can record it or relay it if anything done isn't according to Hoyle, no?

Yes.

b.

[barnakiel]

Originally Posted by Mike OReilly

(...)

But in open waters, with great distances between vessels, the notion of who is stand-on becomes rather academic.

(...)

I see. Wondering at which point one becomes a 'stand-on'. In practical terms. In open waters.

Good point. I will have to think about it. Had a pang when writing my post but disregarded it. Exactly because my attitude is to never get too close. (talking miles, not cables)

Good question.

b.

[Dockhead]

Originally Posted by Mike OReilly

. .. But in open waters, with great distances between vessels, the notion of who is stand-on becomes rather academic. Under the assumption that they may not see me, I would take the minor corrective action required to avoid a collision that I thought was becoming possible. Unless, as you say, I was somehow restricted in my maneuvering, why wouldn't I take the minor action before it became major.

With "great distances between vessels" (say >10 miles), no one is obligated to stand on. This phase starts only when a risk of collision arises.

So standing on is not "academic" at all, it's simply inapplicable, during that phase. Best practice is to prevent a risk of collision from ever arising, and so prevent anyone from either standing on or giving way, but it's not always possible. Furthermore, during this phase, you might take some "minor action", and he might also make some "minor action", and the situation doesn't get resolved the way you thought it would. That's OK at >10 miles out, but at some point you are required to stop screwing around with "minor actions", and one vessel -- the give-way vessel -- takes command of the situation and makes a large maneuver to sort it out once and for all, while the other vessel -- the stand-on vessel -- "holds still", so that this maneuver of the give-way vessel is assured to be effective.

[Dockhead]

Originally Posted by barnakiel

I see. Wondering at which point one becomes a 'stand-on'. In practical terms. In open waters.

Good point. I will have to think about it. Had a pang when writing my post but disregarded it. Exactly because my attitude is to never get too close. (talking miles, not cables)

Good question.

b.

In order to figure this out, I did a lot of talking with commercial ship officers, and came to the conclusion that on average, in open water, they consider 10 miles to be a "risk of collision", and 5 miles to already be a problem. So you can expect them to have maneuvered by 5 miles out, and if they haven't, then you can have a reasonable doubt that they ever will maneuver and so you might start maneuvering yourself, if you have a safe maneuver. They usually have a rule that they must detect the other vessel and be keeping close track of a potential collision situation no less than 10 miles out.

Prior to, roughly, 10 miles out, there's enough time left, that you can consider yourself still free to maneuver.

So in my book, it is the phase between 10 miles and 5 miles where you need to do your standing-on, if you didn't manage to defuse the situation yourself at >10 miles.


This assumes an average commercial vessel making 14 - 20 knots. A very fast vessel changes these parameters. For one thing, when there is a very large difference in speed, the slower vessel is less and less able to do anything effective to increase the CPA. So if you encounter a fast ferry going 40 knots, the right thing to do is usually to just hold on and pray. With that difference in speed, he will control the crossing and there isn't much you can do. Talking to officers from such vessels -- they say that they just steer around traffic like playing a video game. They don't really care what you do, because you're going too slow to either get in their way, or to get out of their way.


As to "how close" -- standing orders on the bridges of commercial ships in open water is usually to avoid CPA of less than 1 mile. Sometimes 5 cables in crowded waters. I don't consider a CPA of less than a mile to be safe if I'm passing ahead of a faster moving vessel. Passing behind or on a reciprocal course, I think 5 cables might be ok, but of course a mile is better.


If you're passing ahead of a fast-moving ship under sail, keep your engine ready to start. A sudden lull in the wind could ruin your whole day. And his career.

[Mike OReilly]

Originally Posted by Dockhead

With "great distances between vessels" (say >10 miles), no one is obligated to stand on. This phase starts only when a risk of collision arises.

So standing on is not "academic" at all, it's simply inapplicable, during that phase. Best practice is to prevent a risk of collision from ever arising, and so prevent anyone from either standing on or giving way, but it's not always possible. Furthermore, during this phase, you might take some "minor action", and he might also make some "minor action", and the situation doesn't get resolved the way you thought it would. That's OK at >10 miles out, but at some point you are required to stop screwing around with "minor actions", and one vessel -- the give-way vessel -- takes command of the situation and makes a large maneuver to sort it out once and for all, while the other vessel -- the stand-on vessel -- "holds still", so that this maneuver of the give-way vessel is assured to be effective.

Completely agree, which is why I would simply make my minor correction once I became aware of a possible evolving collision situation. I wouldn't wait for the other vessel if we were at great distance (10 nm sounds good), and there were no other extenuating circumstances.

Of course, if the other vessel has already taken corrective action prior to me noticing, then it would never come up as an issue for me. And vice versa I suppose for the other vessel if I take the action far out.

[Don C L]

10 miles... 5 miles... in my neighborhood if I can see I am on a POSSIBLY closing course at 3 or 4 miles I will just stop (or turn around if I have any doubt!) and let him or her pass by... at 20 knots or so, it won't take long, then I hustle to get across the shipping lane. The faster boats, ferry boats and fishing, I don't worry about, they can turn, slow down if needed, they go around. But ships in shipping lanes I know are feeling the constraints of the pink lines, I'd never expect them to alter much nor do I feel I am owed any particular license to ask them to alter course with lanes so clearly marked...

[Dockhead]

Originally Posted by Don C L

10 miles... 5 miles... in my neighborhood if I can see I am on a POSSIBLY closing course at 3 or 4 miles I will just stop (or turn around if I have any doubt!) and let him or her pass by... at 20 knots or so, it won't take long, then I hustle to get across the shipping lane. The faster boats, ferry boats and fishing, I don't worry about, they can turn, slow down if needed, they go around. But ships in shipping lanes I know are feeling the constraints of the pink lines, I'd never expect them to alter much nor do I feel I am owed any particular license to ask them to alter course with lanes so clearly marked...

That is fine technique as long as you are sure that you will stop short of where he will be. I mean absolutely sure. If he's in a channel then that's straightforward -- just stop before you enter the channel and everything will be fine.

But that can be very dangerous and very poor technique, however, if you aren't sure, and I find the phrase "POSSIBLY closing course" -- what, you aren't sure? -- disturbing. By 3 or 4 miles he should have already maneuvered if he needed to, and if he's set up the crossing to pass behind you, and if you are not able to detect that there is a safe CPA, and you STOP -- you can screw up his maneuver and cause a collision.

If you are approaching him from his starboard side, stopping (or slowing down) has the same effect as a turn to port. THIS IS A BIG NO-NO. Because if he maneuvers at the same time, he will ordinarily make a turn to starboard, and may maneuver right into you. Stopping can put you right into his path. At only 3 or 4 miles out, it may be too late to correct -- there may not be time for another series of maneuvers.

If you are approaching him from his port side, stopping is reasonably safe so long as you are sure that you aren't passing ahead of him, as stopping is equivalent to a turn to starboard, in terms of how it moves the CPA.

In any case, if you are in a possible collision situation at only 3 or 4 miles out, you MUST know how you're crossing so you know what maneuver will increase (rather than decrease) the CPA. If you don't have AIS, then you must be doing very intense work with a hand bearing compass. Otherwise you can't know which way to turn or what to do, and you are basically just flotsam in the encounter, relying completely on the ship to avoid you. Far better to hold your course and speed if you can't figure it out. Then at least HIS maneuver has a chance of success.

[donradcliffe]

Originally Posted by pcmm

The problem with requiring everyone to have AIS tx is that it becomes useless. If you look at marinetraffic.com for singapore (an area that requires it) there are over 2600 listed tragets! that's to the point of becoming just "clutter" and not useful. Jamie on "Esper" also made the same observation that when he turned on his AIS overlay for his chartplotter, there were so many targets that it was useless. he had to filter out all but the "dangers" at that point you might as well just turn it off!

That's why you need AIS software made by sailors for sailors. Computers can be programmed to sift through the 2600 targets and present the 5 you need to worry about most.

When I bought an AIS receiver, the transmit option was $10,000. When Class B transmitters came on the market, I was an early adopter. It really is a no brainer. My total cost for the receiver only was about $350--$200 for the unit (which was so old it would only pick up one of the two AIS channels) and $150 to buy and install another VHF antenna. I displayed the AIS on OpenCpn, but also spent another $500 for a Vesper Watchmate display which only draws 0.25 amps for use on passages. Switching to a Class B transceiver was another $500 with minimal additional power draw, as it used the same displays and antenna.

Once caveat for the transmitting AIS. You need to really learn the Colregs, because the ships will treat you like another ship. Without a TX, I used to go green-to-green in head-on approaches with a one mile clearance. With the Tx, I've had several ships change course to try to go red-to-red once I appeared on their AIS screen.

If you are sailing in waters where the ships are constrained to channels, the Tx function is not going to get you more than a wake-up call or 5 blasts. If you are on open waters, they will go out of their way to avoid you.

All-in-all, you get about 80% of the benefits of AIS from the receiver, and 20% from the transmitter, and more benefits in open waters where the ships can maneuver.

On the rivers of the Great Loop, I used a Standard Horizon 2100 hooked to OpenCPN. I could see the tows several bends away, and could work out which side they would likely want me to pass (the inside of the bend). The second I could see their wheelhouse (and they could see me), I would call them by name and suggest a passing side (one or two whistles), and they always agreed. It would have been nice to have a transmitter the few times we anchored on the rivers, but we got by.

[Don C L]

Originally Posted by Dockhead

In any case, if you are in a possible collision situation at only 3 or 4 miles out, you MUST know how you're crossing so you know what maneuver will increase (rather than decrease) the CPA. If you don't have AIS, then you must be doing very intense work with a hand bearing compass. Otherwise you can't know which way to turn or what to do, and you are basically just flotsam in the encounter, relying completely on the ship to avoid you. Far better to hold your course and speed if you can't figure it out. Then at least HIS maneuver has a chance of success.

Oh of course! I am talking about when I only see one running light, not both, or the port or stbd side of hull! He or she (and I am talking about the big ones) has their course and I am pretty sure they will stick to it. If I STAY on mine and the angle isn't changing then, well, then I think I may deserve to get hit! Now, if I see (not sure how it could sneak up on me, unless I am foolishly plodding ahead in the fog without electronic eyes, but) both running lights or both sides of the hull at a mile or so, I will, as they say, probably need to change my shorts. Then one has no choice but to maintain the same course and increase speed if possible.. but how did I get into that pickle in the first place??
BTW 3 or 4 miles is still really quite a ways and there's time to do things, but if I do play it conservatively and hold back I have to really hurry up and cross the shipping lane because it takes me quite a while to go 3 or 4 miles and the next ship traffic could be right on the tail of the one I am looking at. Sometimes it is BETTER to plan to pass fairly close to the stern of the passing ship.