So much for AIS and DSC.

[BlueSkyNick]

Crossing La Manche from Cherbourg to Solent yesterday (Monday). F4 from ENE, and all was well, although the wind later died.

Approaching W-E shipping lane, two vessels immediately obvious and a third down on the horizon - as usual, that is the one to be worried about.

Tracked it on radar, eyeball and AIS for several minutes and its obviously going to be close. AIS showed CPA about 0.4nm - one problem, of NASA engine at least, is it doesnt say in which direction - is he going to pass ahead or behind?

Heed advice on this forum not to waste time engaging in a VHF discussion, just concentrate on avoiding collision.

Satisfy myself that he is going to pass behind, but Mrs Guest Crew in cockpit is getting very nervous almost scared, and so I started the engine and took us up to over 8knots until we were clearly across.

All this time, said vessel made NO change to speed (11.7knots) or course. I was a sailing vessel and on his starboard bow, but that hadnt made a jot of difference.

After we had crossed, I decided to use the MMSI number shown on AIS to make an individual call and at least find out if had seen us at all, eyeball or radar, rather than entertain everybody on Ch16.

Made call choosing Ch6, got an acknowledgement within a second, then called by audio - nothing heard.

One minute later, repeat process - got an ack but nothing heard on audio. Gave up, recorded all details in log.

Looking on ITU-MARS database today, it was a 2200 ton tanker, registered in Gibralter owned by a Turkish company. Not much point in complaining to them, then. So its going to be a letter to the MCA, for what its worth.

We had a similar instance going the other way on Thursday night, and had chosen to turn to starboard four times about a minute apart, ie in a big square as I monitored the ship going by, no change of course or speed.

And my point is? To confirm what many of us say on the forum about DSC/MMSI and AIS - useful sometimes but definitely not to be relied upon. Always assume that nobody on the bridge is paying any attention, even if they are there.

 

[Richard10002]

Hi Nick,

A couple of things:

If your AIS, Radar and eyeball suggest a CPA of 0.4nm, you were satisfied that he would pass behind you, and the ship reaches the same conclusion, as long as he keeps watching you, he doesnt really need to alter course - he has probaby also satisfied himself that he is definitely going to pass behind you, so he maintains course and speed, and expects you to do the same - this is the most likely scenario.

Alternatively - how far away from him were you when you started the engine and sped ahead of him? Big ships' deck officers tend to have a distance at which they alter course if a collision situation exists, (the distance may vary for different traffic densities). If he was a 1 mile man, and you did your runner at 1.5 miles, he didnt necessarily do anything wrong, he just hadnt made his move yet, and didnt have to because he saw you clearing ahead of him.

Not criticisms, and nothing wrong with what you did in the particular circumstances, merely observations - being the stand on vessel is quite a nerve racking thing. You either have to avoid the situation arising well before it becomes a collision situation, or you have to stand on until the action of the give way vessel alone will not be sufficient to avoid a collision... at least those are the rules.

On your points - The NASA you are using obviously has a drawback with CPA - is it the standalone thing, or the plotter integrated on?

DSC - He doesnt have to talk to you, and there could be a hundred genuine reasons why he would choose not to - one of which is that you are in the past, and he has another yacht to deal with etc..

Paying attention on the bridge - the officer may have been paying the utmost attention, or he/she may not - and you will never know.

You dont give as much detail for the second incident, so it is hard to comment.

Cheers

Richard

 

[BlueSkyNick]

hi Richard,

The CPA was from the AIS, and afterwards it occured to me that if the other vessel is of a significant length, and the transmitter is on the bridge near the stern, the bow can be almost a ships length closer than apparent.

I have the NASA engine working into my PC running Maptech charts (the Pro version). If I have missed a feature which gives the direction of the CPA, I would love to know about it.

He was only about half a mile away when I started the engine and couldnt see his port side at the time, so would have probably been closer than 0.4m in reality which is why I started up - I am sure there are others on here who will say I left it too late, and in fairness they may well be right.

Disagree that he didnt have to talk to me - no other yachts in immediate range, nothing else going on. IF he was too busy, he shouldnt ahve acknolwedged my DSC call - its a bit like answering a ringing phone and hanging up again straight away.

"Paying attention on the bridge - the officer may have been paying the utmost attention, or he/she may not - and you will never know."

My point entirely, proven in practice - and that the electronic toys can not be relied upon to deal with the situation.

 

[bilbobaggins]

[ QUOTE ]

My point entirely, proven in practice - and that the electronic toys can not be relied upon to deal with the situation.

[/ QUOTE ]

All my limited experience is convergent. At best, the toys can only provide information - sometimes misleading the unwary. The 'nut at the wheel' is there to provide judgment and implement decisions.

/forums/images/graemlins/wink.gif

 

[jonjo]

Not knowing the bearing at time of CPA must be a big headache, the AIS laptop software that I use (Yacht-AIS) presents this info in a popup window. The software’s author posts here occasionally and I would ask him to consider promoting bCPA to the standard target display summary.

In terms of crossing the Chanel shipping lanes, 0.4 of a mile CPA is my minimum comfortable distance providing the ship is on a steady course and not likely to swerve to avoid other larger traffic. In a close call I often watch the rudder/rotation info as this gives me an idea about what the OOW is thinking on the bridge.

 

[Sans Bateau]

Nick

As you know we came back across from St Vaast yesterday, a little later than you.

Our crossing saw only three ships crossing W - E and only one crossing E - W.

I have been thinking of AIS, but it sounds like radar, mark one eyeball and judgement through experience is still the way to cross safely.

Out of interest, during our crossing on Friday night I identified a ship lit as 'vessel restricted in its ability to manoeuvre'. Behind that I could see another very faint red light, OK, thought I, go behind the VRAM and in front of the vessel looming on the horizon, could see it on radar and it was over 6 miles away.

Wanting to see as much as I could of the VRAM, what was it? I asked myself, I scanned it with the binnies. To my horror the faint red light was on the port side of a bulk carrier/tanker that was under tow. It was not other wise lit at all, the red light was about half a mile behind the tug.

All good for added experience.

 

[BlueSkyNick]

mmm... now you have me wondering.

If I click on a 'target', a task pane opens which gives me all the transmitted info from the vessel, and the calculated tCPA and CPA but definitely not bCPA.

However, there is a seperate task pane option which I have never used, which shows targets within whatever radius is selected. This is the only place I can think where the bCPA might be shown.

Another job for the list /forums/images/graemlins/wink.gif

 

[jonjo]

[ QUOTE ]
afterwards it occurred to me that if the other vessel is of a significant length, and the transmitter is on the bridge near the stern, the bow can be almost a ships length closer than apparent.

[/ QUOTE ]
I get your point but technically the position of the GPS receiver on the ship is the issue that should concern us. It would be interesting if someone from the pro merchant world knows whether the AIS standard requires that large ships add an offset to their AIS transmissions to centre the position at the bow?

 

[landaftaf]

on a class a set there is an option to put in the vessels dimensions and position of the ais aerial - yes

this info can be interrogated by another class a ais and the info you are seeking obtained

 

[jimi]

Re: So much for AIS and DSC.

0.4 behind or ahead is 0.8 miles .. perhaps you need a new pair of glasses, a hand bearing compass and a radar set if you can't get your new toys to work?

 

[BlueSkyNick]

Apart from the subject experience, we only saw 3 ships in each direction so pretty quiet really.

I still believe that AIS is useful if the technology is reasonably easy and affordable to owner and boat. At minimum, it provides details about a vessel, such as MMSI which I initially thought useful but am now not so sure. The more useful features are the subject's course details, ie COG and SOG, and hence CPA and TCPA (subject to above discusssion with Jonjo). These are easier and more accurate than calculating them from radar.

So it is a useful system for providing more information, definitely not a substitute for radar which I have said all along, and its still down to the skippers interpretation of the information and ability to make a decision which really matters, as Bilbo says.

 

[captainslarty]

Re: So much for AIS and DSC.

You need to relearn the rules of the road lol....
ie, YOU avoid others, simple, no starboard tack, sailing etc, just avoid them plain n simple.
I cant believe people still think they have right of way /forums/images/graemlins/tongue.gif

It just aint so out there. use the mk1 eyeball and HB Compass, and just move outa the way. stress free, no worries.

 

[BlueSkyNick]

Re: So much for AIS and DSC.

[ QUOTE ]
0.4 behind or ahead is 0.8 miles .. perhaps you need a new pair of glasses, a hand bearing compass and a radar set if you can't get your new toys to work?

[/ QUOTE ]

You what?

I was comfortable he was going to pass behind having tracked him for a while.

However, when he is over 8 miles away on radar, one can't work out CPA to any accuracy, h/b compass and eyeball or not.

If the AIS can do the sums, its another piece of information to take into account at an earlier stage.

 

[BlueSkyNick]

Re: So much for AIS and DSC.

Have you got that two years growth of weed off your waterline yet?

 

[jimi]

Re: So much for AIS and DSC.

[ QUOTE ]
[ QUOTE ]
0.4 behind or ahead is 0.8 miles .. perhaps you need a new pair of glasses, a hand bearing compass and a radar set if you can't get your new toys to work?

[/ QUOTE ]

You what?

I was comfortable he was going to pass behind having tracked him for a while.

However, when he is over 8 miles away on radar, one can't work out CPA to any accuracy, h/b compass and eyeball or not.

If the AIS can do the sums, its another piece of information to take into account at an earlier stage.

[/ QUOTE ]


Neither can AIS cos its basing is calculations on velocities at that moment in time. Over reliance on the accuracy oftechnology may lead to unacceptable shavings of error margins

 

[jonjo]

[ QUOTE ]
I have been thinking of AIS, but it sounds like radar, mark one eyeball and judgement through experience is still the way to cross safely.

[/ QUOTE ]
I have been conducting my own AIS survey during the past 3 weeks of cruising and all have praised their AIS kit where installed (about 30% of yachts I have spoken to). One skipper said he rarely switches on his radar these days.

UK coastguard stations are now chasing up bad AIS transmissions so the quality of info will get better.

 

[BlueSkyNick]

Re: So much for AIS and DSC.

ah yes, but at least its basing its calcs on velocities whats known, and headings, so can come up with a reasonable answer. One can use this information to help decision making, and you're underlining my point that it technology is only an aid not to be relied upon.

 

[BlueSkyNick]

[ QUOTE ]
One skipper said he rarely switches on his radar these days.

[/ QUOTE ]
Now that IS a worry.

[ QUOTE ]
UK coastguard stations are now chasing up bad AIS transmissions so the quality of info will get better.

[/ QUOTE ]
And this is good, some transmissions seem to be stronger and more complete than others.

 

[ChrisE]

[ QUOTE ]


One skipper said he rarely switches on his radar these days.



[/ QUOTE ]

Really? I'd have thought that radar was the perfect complement to AIS. AIS can't see vessels <300t and with MARPA you can confirm the readings from the AIS box.

Personally, I'm never happy when using a sole source for information.

 

[BlueSkyNick]

[ QUOTE ]
a sole source ...

[/ QUOTE ] Mornay?