AIS & ARPA ...

[Robin]

[ QUOTE ]
If you're a mile off, in fog, on a collision course, you are 2 minutes away from that collision. You haven't a prayer with such tactics. Commercial shipping will not slow down and comply with the col regs, period ....

[/ QUOTE ]

You are correct of course for a ship doing the kind of speed that the one which hit Wahkuna was, around 27kts I believe. But not many do that speed fortunately, as will be seen from AIS Live data. But the difficulty of identifying the collision risk is still the same, the data is gathered differently but the plotted results are no different, how can they be? In clear vis it is still very difficult to determine if a ship closing at an acute angle will clear or not, the bearings start to change only once in closer range. This problem is no different in zero vis, only that now you have to trust to instruments and your ability to use them and much depends on what else is close by or coming up fast as well. On occasion we have used the 'stop' or rather 'almost stop' option (to keep steerage and a constant heading on the screen), but only when at a greater distance. We have also chosen to cross at nearer 90 degs if it is very busy, then go back on course between lanes and see if the same tactic is needed for the next one, although this is a bigger detour than it might seem.

The actual CPA isn't the whole solution either, I don't know how to explain it especially in radar terms but in clear vis a ship that I cross a mile ahead of quite safely, might have a CPA of only 1/4 ml as he passes down one side at the acute angle we talked about. I would not be happy about a CPA of just 1/4ml, yet that ship was cleared effectively by 1 full mile, big difference!

What is really needed is to get out of this cold damp foggy corner of the world and sail where radar is the name of the barman's dog!

 

[Anonymous]

[ QUOTE ]
........not to mention speedboats/fast mobos still going in figure of eights flat out [in thick fog].

[/ QUOTE ]That's exactly my experience which is a major reason why I like to have a radar display aloft rather than just below. In our case we do have a perfectly good conning position below but even so, in thick fog, you want to be out there to listen. Why do so many people - especially in traditional sailing yachts - install radars (if they only have one display) below?

David

 

[Superstrath]

Ghostwriter, your response here is very techie. The fact is that there is NO future forseeable situation where all vessels which may present a risk of collision will be firing out AIS or any alternative signal. There will always be traditionalists, paupers, and nutters on the high seas. IRPCS are quite brilliantly written, as a result of centuries of seafaring experience, and if complied with properly make life at sea as safe as it can be. The problems lie with high speed merchantmen (and RN), don't-give-a-damn fishermen, and beligerant, illeducated or under-experienced leisure boaters. All are at fault: but it is a pipe-dream to imagine that one day all vessels will be visible to responsible, trained managers on each other's bridges via some kind of information system.
Slow down, keep a look-out and know the rules.

 

[Robin]

[ QUOTE ]
That's exactly my experience which is a major reason why I like to have a radar display aloft rather than just below. In our case we do have a perfectly good conning position below but even so, in thick fog, you want to be out there to listen. Why do so many people - especially in traditional sailing yachts - install radars (if they only have one display) below?

[/ QUOTE ]

That is a big subject and maybe for another post, although it has been done before!

I had two different radars over the 14 years I had my previous boat and both were mounted below, it would have been my choice if I had one which I didn't simply because neither were waterproof. The first set was not a daylight display, so required you to look down a PVC tube, like a what the butler saw machine, the second was a daylight viewable CRT and was easily seen from the cockpit, enough to keep a casual watch. Our current LCD set is also at the chart table, it was already fitted there when we bought the boat, but it would still have been my chosen position.

If I had a mobo with a flybridge, or had a motorsailer with a wheelhouse then I would probably have the set up top, or at least a repeater, but on a normal yacht I prefer it down below. My reasons are:-

1) I believe if you need to use the radar then it needs concentration and no distractions from other activities like helming or keeping visual lookout or trimming sails.

2) If a set is mounted at the wheel it is out in the cold and perhaps the wet and only visible if you stand behind the wheel in a normal yacht layout. Plotting needs MARPA (our set doesn't have it) once it is beyond the ken of bearing lines and/or trail features.

3) Looking at the screen say at the wheel simply tells you there are targets out there, it doesn't tell you what they are doing or if they pose a risk. To know if they are a risk entails watching the video unfold and that needs IMO concentration.

4) The idea of being able to listen up top is fine in theory but less so in practice. With the engine running you hear little and under sail at any speed is no different. I cannot remember when I last heard a foghorn from a ship in the lanes, I think they don't want to admit the vis is that bad in case they might be obliged to slow down....

Our set is (just) visible from the cockpit but the LCD screen isn't as clear as our old CRT one. However it is mounted at the nav table, adjacent to a 10" chart plotter and is linked to the GPS such that the next WPT is displayed on screen. We also have a second autopilot control head at the nav table and can make course changes directly from there, no need to shout to the on deck crew ie SWMBO. We have a plastic wipe clean plotting board with printed compass rose and range scales for detailed plotting (DIY MARPA) if needed though if it was it is because we were rather closer than I would like to be!

Open to discussion, but my preference for a single location set is still below.

Robin

 

[ParaHandy]

Joburg tracked two ships exceeding 25kn when Wahkuna was hit. The tracks of both were given. Do you think the cross channel ferries slow down? container ships? To suggest that very few proceed at that speed in fog is not my understanding.

The master of Vespucci's sister ship in the YM that appeared just before the Wahkuna MAIB investigation was published and which merely advised the Master to read the MCA's NM regarding speed in reduced vis, opined (and here I put words into his mouth) that, in fog, we should all stay safe at home as he had a proper job to do and wasn't minded to slow down .....

your explanation of CPA is one that struck me as well. CPAs in front of a vessel may well be 3 cables but if the vessel is a few hundred meters long and proceeding at these sort of speeds, you pass his midships a damn sight closer ...

Again ... its the disparity in speed which makes this so dangerous ...

 

[ParaHandy]

[ QUOTE ]
.... but on a normal yacht I prefer it down below. My reasons are:-
1) I believe if you need to use the radar then it needs concentration and no distractions from other activities like helming or keeping visual lookout or trimming sails.

[/ QUOTE ]

crivvens ... jings ... we agree on something ... !!

 

[jimi]

Re: AIS & ARPA ...

".... but on a normal yacht I prefer it down below. My reasons are:-
1) I believe if you need to use the radar then it needs concentration and no distractions from other activities like helming or keeping visual lookout or trimming sails.


crivvens ... we agree on something ... "

I do'nt agree with either of you,

The place for radar on a small craft is at the helm.

1) Familiarisation , helm can see what's happening + radar
2) Shorthanded
3) Don't need concentration and no distractions from other activities, all you need is an EBL and see if the target is moving in front or behind the EBL .. or is that too simplistic? I start to watch at 10 miles & take action at 5, if its a bunch of boats I'go behind them. In fog I'd rather add an hour to my journey than pass less than a mile from a large vessel.

 

[ParaHandy]

[ QUOTE ]
Slow down, keep a look-out and know the rules.

[/ QUOTE ]

hmmm ... when faced with the vast majority of commercial shipping chuntering along at full speed in reduced vis, knowing the rules doesn't seem to be enough to me. A practical addition to radar is needed .....

 

[ghostwriter]

mmmmyessss....

yes and no, and no and yes. I think we agree but we look at it from another end of the rainbow.
the underlying question is rather philosophic, do you aim for the lowest common factor or do you try and get the best possible and then leave it up to people to decide how far they want to go along , and if they don't it's THEIR responsability ?

it is true that there will always be traditionalists, paupers, nutters on high seas , ill educated and/or under-experienced too (and to avoid being called a hoyty-toyty racist ... I have no problems with any of these, perhaps I might fit into the pauper mob too), but that can not be the reason to dismiss, detune , even stop possible positive evolutions, can it ?

Slow down, keep a look-out and know the rules. ABSO-[censored]-LUTELY AGREE, BUT apart from that I would add : and meanwhile try to take advantage of whatever goodies those techie wizzards make and that is affordable enough to make your time even safer and more enjoyable

p.s.on the techie bit : yes, very techie and even ex-merchant shipping electronics techie...but sailing a '72 vintage Contessa 26 with as only techie thing on board (apart from the portapotti ! ) a GPS that I can't even see when sitting behind the tiller...very techie indeed /forums/images/graemlins/wink.gif

 

[ParaHandy]

Re: AIS & ARPA ...

... and its pissing with rain, you're tired after umpteen hours of this, 2 or more targets, yawing and the umpteenth cup of tea has just deposited onto your dubarrys?! typical weekend really ... !!

 

[jamesjermain]

Hang on...hang on!

Don't shoot the messenger.

AIS has the potential to be a great aid for yachtsmen as well as commercial craft and I love all new gadgets. The RYA approves of it for a number of reasons. But there are technical reasons AT THE MOMENT, which means it is not fully effective for yachtsmen.

A big word of caution though. If the MCA get it into their heads that all vessels should have AIS so they can keep tabs on them, then fitting them to yachts will become compulsory.

And then they will have to check they are fitted for a fee and have a register which means compulsory registration and fees and qualifications and fees and light dues and fees and...

 

[Robin]

[ QUOTE ]
Joburg tracked two ships exceeding 25kn when Wahkuna was hit. The tracks of both were given. Do you think the cross channel ferries slow down? container ships? To suggest that very few proceed at that speed in fog is not my understanding.

[/ QUOTE ]

No I don't think they slow down at all and I suspect they don't use fog signals because that might acknowledge that they should do so! However the numbers that do travel at those speeds are much fewer.

I have just quickly looked at AIS Live and the speeds currently in the Central English Channel are:-

11.3, 5.5, 7.9, 15.2, 17.9, 15.3, 20.5, 12.6, 15.8, 9.0, 21.3, 13.6, 15.2, 15.1, 9.7, 6.7, 8.8, 15.6, 0.6, 17.2, 11.2, 20.8, 11.2, 10.2, 13.4, 14.0, 10.0, 6.6, 7.0, 14.0, 5.4, 16.5.


[ QUOTE ]
your explanation of CPA is one that struck me as well. CPAs in front of a vessel may well be 3 cables but if the vessel is a few hundred meters long and proceeding at these sort of speeds, you pass his midships a damn sight closer ...

[/ QUOTE ]

This is difficult to put in words as I said before, but I know I'm quite happy in clear vis once I can see that the other vessel isn't pointing at me anymore or me at him or in front of him if close. In the example I quoted of crossing Dartmouth/Ushant which will cross the lanes NE of Ushant at an acute angle this is very apparent. In one lane you are almost going with the flow and everything approaches from your port quarter and in the other you are almost going against the flow with everything coming from the starboard bow. It seems like you are 'in' the lanes forever but in reality you are not, you are almost running parallel and several miles off for most of the time. Bearings of other vessels be they compass or radar relative bearings do not change for a long time and only do so as the target gets closer but I don't know how close it has to be for this to be seen, no doubt someone with a mathematical leaning could work it out. Once the bearing does start to change though it does so quickly and you wonder why you thought there was a risk at all! The problem however is in bad visibility when as far as I'm concerned I don't want to pass less than 1 mile ahead of a ship anymore than I would in clear vis but in both cases this 1 mile is NOT going to be the CPA. In the acute angle scenario this is especially the case as the CPA could be as little as 1/4ml even though we passed a mile or more ahead, but the other vessel is still clear astern and no threat. You can usually see this OK on radar IF you have been watching the situation continuously not just taking occasional looks, the radars 'trail' or 'plot' function helps to visualise this too.

I agree that the disparity in speed makes it dangerous sometimes because the decision process time is shortened, although sometimes I have even yelled at a target to say get a move on!

Fortunately all this stress with the big stuff is concentrated in expected areas or it would be no fun going anywhere at all!

 

[ParaHandy]

fer gawds sake .. edit the post Robin and put a space in that long list ....

 

[jimi]

Another thing that is worth cosidering is that when close to a large vessel the radar goes crap . with the echo surrounding oneself.. another good reason for staying well away in fog

 

[Robin]

/forums/images/graemlins/smile.gif I think we agree on quite a bit in reality but understanding a written explanation without the ability to doodle diagrams is difficult. I'm not even sure sitting at a keyboard that I can even remember how it is let alone portray it accurately!

 

[tome]

Robin

Can you edit that your previous post as suggested?

 

[Robin]

List edited

Is that better?

 

[ParaHandy]

attaboy ... can read it now ...

 

[Robin]

Edit done is that better nm

*

 

[ParaHandy]

"I have just quickly looked at AIS Live and the speeds currently in the Central English Channel are:-"

you're getting dangerously close to proving my point .. that's 33 odd ships (one must be at anchor?) for which you could generate data thro' AIS and all from an aerial which must be on land ?

Being a mathematician, and if this was fog, the probabilities of successfully crossing that lot have immeasurably improved and that's what I've been banging on about ....