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Radar or VHF Assisted Collisions

lw395

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16 May 2007
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42,088
I think a classical Radar Assisted Collision is all about frames of reference.
You observe the enemy on your radar and see his relative motion. You then turn and that changes his relative speed and direction, which is easy to interpret as him having turned, or if he turns at much the same time, you can't tell.
I suspect it's a little like the 'lee bow effect', it means 4 different things to any 3 people you ask, with a general flavour of inability to visualise vector summation.
 

lw395

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16 May 2007
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Early this century, we had a cruising holiday, Solent, > Channel Islands, > Lezarderieux (sp) > Fog > more Fog. > Dartmouth
Fed up with fog, I think I'll buy a radar.
After a slightly fraught channel crossing, spent the evening in the Royal Dart, drinking and reading yotty comics.
Found an interesting article, analysing the very few instances of yachts actually managing to collide with ships.
The majority who collided, had radar.
A bit of a theme of ' we only use the radar if it's foggy'.

Another way of looking at it, if you wanted to hit ships and fired torpedos out of Pompey at 6 knots, you wouldn't have much of a score.
Some people stress too much, it's not the M25, you mostly couldn't hit anything if you tried.
 

Roberto

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20 Jul 2001
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Lorient/Paris
Mentioned in the Stand On thread, does anyone have a link to an article or YouTube clip explaining how these happen, please?
There is the MAIB report about Wahkuna (IIRC), a 50ish ft sailboat who was crossing the Channel in fog and possibly misinterpreted their radar screen; made a U turn, got its bow smashed off by a cargo and sank in minutes.

As to VHF, not a collision but accident example: a German sailboat was on passage in front of Gironde estuary (Atlantic France), vhf phone communication misunderstanding between them and Cross (the French MRCC) led to a sad result. It's in one of BEAMer accident reports I'll see if I can find more details.
 

Uricanejack

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I don’t know of a good article, somebody’s bound to have written one. Magazine like safety at sea or the nautical institute most likely have something. Crocford sites a few cases.
Poor radar or VHF use are typically only part of the story. Safe speed often applies along with other factors.
The term generally applies to collisions which have occurred in poor visabilty. Collisions often occur in clear visabilty often involving poor communication and poor use of the radar.

A direct quote from the rule. 7
“Assumptions shall not be made on the basis of scanty information, especially scanty radar information.”

How do radar or VHF assisted collisions occurs,? see above.
Somebody, very often two somebody’s, make assumptions. Instead of carrying out a complete radar plot. Or make an assumption about another vessels actions.
An additional common factor, is a decision to make a departure from the rules. This may be a decision by one vessel or in some cases has been an arrangement via VHF. Which is not understood. The same way by both vessels.

when radar was introduced, Existing ships officers, often didn’t fully understand how to use radar, after a few unfortunate events.
Training in radar observation became mandatory. Now mandatory for all electronic Nav system’s including ARPA and ECDIS
Despite training, unfortunately collisions still occur, Why? Lots of reasons.
Not the least of which. Decisions to use improved technology. To reduce margins.

Additional Common factors.
Speed, particularly failure to reduce speed or reluctance to reduce speed on encountering reduced visabilty.
Small alterations of course or speed which are not easily detected by other vessel’s observing by radar.

Very often, after several errors or omissions. Leading to poor understanding of the situation or lack of situational awareness. On both vessels.
Results in a close quarters situation developing.
One of the two vessels becomes concerned, about the close quarters situation, while lacking situational awareness, decides to make a last minute alteration to Port.

How to avoid a radar assisted collision?
Don‘t go out in fog, Not always possible.
If you have a radar, take a course on radar plotting and the use of radar.
Where practical , avoid making departures from the rules particularly in poor visabilty.

Avoid temptations to alter to port particularly when using radar in poor visibility, unless you are the overtaking vessel.

Avoid making passing arrangements on VHF which include a departure from the rules.

Make use of long range scanning, regularly in addition to shorter ranges.
Plot or use MARPA,
if a close quarters situation is developing

Take early and substantial action which can be easily observed by radar on an other vessel.
Alterations of course of 60 degrees or more,
or cut speed in half, if you are on a slow vessel stop.
 

capnsensible

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15 Mar 2007
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Atlantic
Should anyone wish to learn how large vessels use VHF to avoid a risk of collision, then go and spend a week in the Straits of Gibraltar. You will be treated to a constant 24/7 of masters discussing and in a few cases shouting at each other. It never stops. Overlaid with vessels calling ports, service launches calling ships, fishing vessels panicking/ playing music/ giving large on 'Filipino monkey' , weather forecast call ups in English, Spanish and Arabic, a barrage of DSC alerts and stroppy yachties complaining. Plus, of course, British military ops stating loud and clear that the incursion into British waters by Spanish vessels will be reported to a higher authority. Sprinkle into this non English speakers on 16 trying to get a berth in. Gib Marina.
It shows just how much a single radio channel can be used at once. Disregarding, of course the Solent radio check....
 

Graham376

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15 Apr 2018
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Boat on Mooring off Faro, Home near Abergele
Should anyone wish to learn how large vessels use VHF to avoid a risk of collision, then go and spend a week in the Straits of Gibraltar. You will be treated to a constant 24/7 of masters discussing and in a few cases shouting at each other.
Can be quite fun crossing from Gib to Ceuta or Smir sometimes. Listening to two ships discussing who was going to go where and one replied "I'm waiting to see if that ********** yacht can decide what course he wants to steer, keeps tacking ahead of me" No it wasn't us:)

I find radar easier in most cases than hand bearing compass, just put the ebl on the target causing most concern and see if he comes down it or moves off.
 

capnsensible

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15 Mar 2007
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Atlantic
I'm all for radar and AIS. But I'm also aware a lot of yachts don't have either or practice with them enough. Some don't even have a hand bearing compass.
However using relative bearing change to a fixed point on your own vessel is a good skill to learn, I reckon.
The Straits are a great place to practice too. Unless it's foggy! 😱
 

laika

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6 Apr 2011
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Limbo
I bought a hand bearing compass as a 'must have' when I buying kit for my first cruiser and I have to admit I can't remember the last time I used it - yet, somehow, I haven't been run over just yet.
Sorry if this is a daft question but....how do you plot a fix, check clearing bearings etc. etc.?
 

Daedelus

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11 Jun 2006
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Hants
Sorry if this is a daft question but....how do you plot a fix, check clearing bearings etc. etc.?
In middle of sea no other reference points, take a bearing of the ship heading for you. (If it is sufficiently far away not to panic yet, leave a few minutes (just enough to make a cup of tea) then take another bearing. If the bearing is the same then you are on a collision course. If i's a big ship and some way away keep going for another 5 minute or so then repeat bearing and if still on same bearing then decide what you will do about it before either of you start to worry. Take further bearings and when you decide he's not going to alter take major alteration yourself but make sure you keep a really close eye now as he might have been altering for you and the change wasn't noticeable by you.

If near enough the coast to pick out features behind other boat see if a feature remains in line with them. If it does, you are on collision course, if he moves ahead of it, he'll go in front of you if the object moves ahead of the boat he will go behind you. This method doesn't indicate by how much if the change is very slow.
 

laika

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6 Apr 2011
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I seem to spend so much of my time sailing over the same stretch(s) of water that taking fixes feels unnecessary.
Fair enough. I also realise that others don't share my affectation of trying to only use GPS for log entries which has the consequence that my passage plans and pilotage notes for unfamiliar places tend to rely on use of a hand bearing compass. I regard my little plastimo iris as "core essential kit" like a multitool and pretty much never step on a boat without it. Navigation...checking collision courses...working out if your main compass has some dodgy deviation...super light and slips easily into the pocket. I regard that plastimo as a design classic...
 
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