[QUOTE=MarkJ;113158]Hi,
This could sound like the most basic question to fall out of the sky in a while…
I am a cruising sailor with a circumnavigation under the belt on this cruise. I sail solo because all women hate me 
Theres some specific questions about how ships use AIS that cruising sailors argue about…
- What is a ships prime avoidance system: Radar or AIS? Yes I know you have both, but what is used mostly in a practical sense?
- At 2.33am is the watch keeper allowed to alter course of a ship with an AIS target or does he need to wake the captain? How long does that take? More generally how long does a ship take from target acquisition to change of course?
- It appears to me (and overhearing VHF conversations) that many shipping lines have a set minimum CPA. Is that correct? Is 1nm normal?
- Do ships filter out Class B signals at all? Or in harbours? etc.
- I appear to have some ships start to divert at 10nms. Is that likely or some aberration?
- Do ships ‘click’ on a target to determine if the target is a sailing vessel, or is it assumed all vessels are motor vessels?
- My boat normally is doing about 6 knots (erratically). In practice, does a ship doing, say, 15 knots divert or stand on if they are the Stand On vessel.
- What range do ships normally first get an AIS contact and does a Class B contact first appearing so much closer give surprise/irritation?
[FONT=Helvetica][SIZE=2]* What range would a ship see a sailing boat thats not equipped with AIS? Or would you see us at all!
Any other advice for sail boats, small vessels?
Thanks for your help 
Mark[/SIZE][/FONT][/QUOTE]
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ARPA is the only approved collision avoidance system we have on board. This is from both a practical and legal sense. AIS is an aid and a good visual indicator on the ECIDS or radar overlays, but is NOT for collision avoidance. It is fine for ballparking a CPA, but should never be relied on. The reason is that the AIS target I see, is generating it’s CPAs based on the target’s own AIS equipment. I’d rather not rely on someone else’s equipment or calibration of that equipment. We have the ability to overlay AIS on the ECDIS and Furuno radars we have, but typically leave it off the radars because it overlays the target echos and doesn’t allow you to easily acquire the return if AIS is on.
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As a watch officer, I follow whatever the Master’s Standing Orders are for that captain, but generally they include something along the lines of “…maintain at all times a CPA greater than 1nm”. I am free to maneuver as necessary within the Rules and take prudent and effective action to avoid collision while following the standing orders.
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This might depend on the area. For instance though, I know San Francisco VTS enforces a 1nm CPA in the offshore precautionary area.
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We can filter based on a number of conditions (the same with ARPA), but the type of AIS class is not one of them. Class B targets tend to be obvious offshore though, they don’t update as often from my experience and don’t appear until closer in.
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It all depends on the watch officer and what their standing orders are. The captains I sail with don’t give specific instructions, just the guidelines to stay within. I maneuver according to Rule 8 and within my comfort zone for that particular situation. With a large vessel, that very well may be 10nm depending on how he is behaving in general, whether I could hail him on VHF, how he sounded on the radio (did he really understand the situation?), etc; or sometimes it’s at a time before CPA instead so we’re not deviating too early for a slowly developing situation. With small targets, I tend to wait until we are closer. I’ve found that small vessels might not appreciate a course change so early, and their perception of danger or a collision situation doesn’t occur until closer ranges. At 10nm, they might not even be aware that there is a situation developing with this shadow they may or may not see near the horizon.
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Honestly, I will always take action as necessary within the Rules, but if I discern that the echo on the radar or the weak lights I see on the horizon belong to a small vessel, I know I might be in for a stressful situation. From a strictly electronic standpoint, I can discern from the radar return the size of the vessel and even if it is fiberglass. Smallish fishing boats won’t pop up until 8-10nm, but usually will deliever a half-way decent return (typically being metal), fiberglass recreational vessels show up even closer with a weaker return. If your vessel has AIS, then it should be indicating the correct vessel type, and I would look at that too just to get an idea. I will also look at destination info and ETA, sometimes this lets me know how much of a hurry the guy is in. But for example, if I see a weak return suddenly pop up at 6nm going 5knots… bingo, sailing vessel. And of course, I’m looking out the window too and at night I’ll have a dedicated lookout on the bridgewing. I take advantage of other radar features too to help me identify targets.
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I for one, follow the navigation rules. There may be some here that play by tonnage, but that is far from an acceptable excuse if something were to happen. But the Rules are mutual, and the commercial sailors on here have all had close calls that muddy our perspective, shoot, even my username is remnant of that!! But I’ve learned that not every sailboat is a W.A.F.I.; that is reserved for a special breed, and over time the ratio of good to bad that I’ve encountered has improved. I am a professional mariner, this is my job, my career, I take pride in playing by the rules and being good at what I do, and I think we all share that here. Your questions here are all about getting to a mutual understanding, and I applaud your interest. All bets are off though if you are obviously not following the Rules; maintaining an effective radio watch is one of them.
That said, if I am offshore and am the stand-on vessel, I will stand on. Preferably, we will discuss each other’s intentions on the radio and clarify our responsibilities. If the other vessel is the give-way, I will always impress that upon them in the first contact so there is no question, and set the tone right away (some might call this “bullying”, I prefer “effective communication”). Certain terms or phrases like “I intend to maintain course and speed”, “I will alter course to starboard and meet you port to port”, etc, etc, should be in your brain when communicating. Foreign vessels where english is the second language know the rules and how they are written – speaking the rules when communicating will make sure everyone is on the same page. It sounds hokey to inland guys who have their own lingo (I’ve been there), but it is the clearest way to avoid miscommunication. All foreign watch officers are required to speak english; how well they do can be a crap shoot. Now, if you are sailing erratically and you are the stand on, I expect you to stand-on. The rules make no allowances for a vessels that feel free to do whatever they want; everyone has responsibilities. Part of my job as a watch officer is to monitor [I]your[/I] actions as well to make sure you are doing what we discussed and what you are required to do within the Rules.
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It all depends on the propagation at the time. Remember, AIS is just a VHF signal, generally line of sight, but atmospherics play a role too. I’ve seen targets with display information 300nm out with good atmospherics, but typically, within 30nm for a commercial AIS. Class B doesn’t seem to show up until perhaps 10nm, but that is really just a guess because I can’t tell the type of AIS, just what I’ve gathered.
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At night all depends on your lights. The combined lights atop the mast work better in this regard. During the day, good luck depending on the sea conditions. On the radar, it is pretty iffy, but in the 6-8nm range at best, but probably not an acquirable echo. Fiberglass gives a terrible return; combine that with pitching and rolling and going into the trough, ARPA has a tough time latching on. I use target trails as a backup to ballpark it, true or relative depending on the situation, sometimes one on each radar. I work in some pretty nasty conditions, so depending on the sea conditions and how I have to tune my radars to get anything appreciable out of them, there is the possibility that I might not see you at all. Then again, in those conditions, I doubt a sailing vessel would be afloat. Like Kennebec Captain mentioned, there is always the possibility the watch officer has the radar tuned down too far. Clutter controls always have drawbacks, as they typically reduce close-in and weak returns. I use true trails in this situation (“snail trails”), even through clutter and weak echos, it will still draw a straight line behind a target; you see that in the midst of a bunch of clutter, theres a decent chance a vessel is out there. But this is why we maintain an effective lookout.
As far as other advice… Read, understand, and abide by the Rules of the Road if you haven’t done so already. Keep a copy on board like you’re required to and refer to it when necessary. Get a good radar reflector for your mast. Also, I know someone who sails regularly and he uses a radar [I]detector[/I], like for a car. They pick up X-band radar signals; lets you know a ship’s radar is within line-of-sight. Some detectors can indicate the direction it is coming from. A pretty good tool to aid in large-vessel awareness offshore.
And lastly, get a good VHF radio, two perhaps, set one to 13 and one to 16 offshore, and install antennas as high as possible. Nothing is more infuriating when you are hailing a vessel and get no response, then suddenly they want to play the Rules card on you. Nope, sorry. I tried, you failed in your responsibilities, I am now following what I feel to be the best course of action. Something I’ve picked up from pilots is to repeat the phrase “negative contact” over the radio if I fail to get a response. The USCG records 13 and 16 (within range), and if I have to say that phrase, at that point I have given up on resolving the situation mutually and have switched to preparing for potential litigation. Don’t let it get to that point.
