Rule 19 - radar question

[John_Clarke]

If you detect a vessel by radar alone, how close (in miles) does it have to be before you would consider a 'close-quarters situation' is developing? Up to this point are you permitted to turn in either direction? You want to keep well clear of the other vessel and a turn to port will take you away from his track.

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[stephenh]

" in restricted visibilty, in the open sea, a close quarters situation is generally considered to apply at a distance of at least 2 miles in any direction forward of the beam as this is the typical range for the whistle of a large vessel. A minimum distance of 3 miles is sometimes suggested ... as allowance should be made for the effects of radar errors...However...less than 2 miles may be considered sufficient...in congested waters...overtaking, or a vessel is expected to pass astern."
Cockroft and Lameijer - "A Guide to the Collision Avoidance Rules "

any use ?

Stephen

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[Talbot]

Your question really is one of those "How long is a piece of string" There are so many different variables that it is difficult to give a hard and fast rule. For example if you are only doing 5 knots and the other ship is approaching at 7 knots, it is different from being in a Mobo doing 20 knots with a fast ferry coming towards you at the same speed. Knowledge that a close quarters situation is developing will also depend on the type of radar aerial (i.e. bearing accuracy) and plotting capability. Remember that on a sailing vessel, a bold alteration of course is not easily detected on a radar.

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[halcyon]

Is there a distance ??? what if your doing 35 knots, and the target is a hovercraft or high speed ferry on a reciprical bearing, or you could be sailing at 5 knots and the target is sailing at 5 knots. Must depend on sea state, speed, were you are, limitations in taking action by you or the other vessel, all the things that makes sailing interesting.

Brian

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[ParaHandy]

A N Cockcroft and J N F Laeijer state: The distance at which a close quarters
situation first applies has not been defined in miles, and is not likely to be, as it
will depend upon a number of factors. The 1972 Conference (IMO Revision of
the Collision Regulations) considered the possibility of specifying the distance at
which it would begin to apply but after lengthy discussions it was decided that
this distance could not be quantified.

On the other hand, the Seafarers' International Research Centre (SIRC) in a
paper dealing with near miss encounters in the Dover Strait (Belcher P (2002)
"Overtaking in the Dover Strait, an analysis of near miss encounters") states:
from a review of literature on ships' domains (Fuji and Tanka, 1971, Goodwin,
1977, Coldwell, 1983, Zhao, et al., 1993) it has been found that the domain
required for a ship in congested waters can be approximated to a circular space
with a radius of 8 cables. It also states: it might be argued that a criterion of a
minimum passing distance of 8 cables is too stringent a measure for such a
busy area. However, a passing distance of 3 cables or less, is on anyone's
measure, a very dangerous occurrence that could lead to a collision with only a
very slight change in circumstances.

(snipped from MAIB Wahkuna report)

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[Guest]

a) Close 1/4's situation depends too much on all the other factors surrounding ... location, availability of sea-room, visibility, shipping lanes etc. etc.
b) Turning to any direction - most seafarers would expect you to turn in accordance with 'normal' rules but more bold to give good indication on the radar etc. of your action. To turn to port for example would not be expected and would be advised to be so great a turn to be not mistaken for a swing about your course .... OK the rules say action to avoid etc. But keeping to starboard turns is always preferred as its expected and normal practice.

Think on this ..... you quite happy and then a taget on port bow ..... if he turns to starboard boldly - he should if turns enough miss you and you will see the turn on your radar. No problem. If you also decide to turn and you turn to starboard also .... you will decrease the risk of collision.

Now lets take a target that appears on starboard bow ..... you turn to starboard decreasing cahnce of collision .... if he also turn sto starboard .... even better.

Now in both scenarios above if any one of you turns to port - well I think you can imagine the result if NOT a big enough and bold enough OBVIOUS movement !!!


<hr width=100% size=1>Nigel ...
So WHAT does the EU really stand for ????/forums/images/icons/cool.gif

 

[John_Clarke]

Good point that with a slow moving vessel a change of course will take much longer to become apparent to other vessels. A slow vessel also has the disadvantage that it cannot get out of the way of another vessel quickly.

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[John_Clarke]

Vessel on port bow

Your point is well made.

It looks as if a yacht motoring at say 5 kts has a problem if it detects a vessel 6 miles away on the port bow which looks, on a radar plot, as if it is travelling at 25 kts and will cross the path of the yacht with a closest point of approach (CPA) of 1 mile. Time to CPA is about 12 minutes.

The yacht is unhappy with such a close approach and there could be a significant error in the plot. There is a moderate sea running so the other vessel may not have detected the yacht on radar and visibility is less than half a mile. It is open sea and there are no other vessels in the vicinity to complicate matters further.

I have almost persuaded myself that the yacht should turn 160 deg to starboard to steam away from the other vessel. The yacht would then be free to turn to starboard again if the other vessel took no action.

What would the safe strategy be?

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[PhilipStapleton]

Re: Vessel on port bow

I think turning parallel to, and in the same direction as the other vessel is safest, ensuring a CPA of 2nm if he stays on the same course. If you turn more than that you are compounding the problem should he make a major alteration of course to pass behind you (as he may already been doing if he "saw" you at >6nm)

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