Collision avoidance at night

[StuM]

Originally Posted by Dockhead

This geometry is exactly why I would consider tacking even though it requires a turn to port, bringing other risks with it.

A nuber of people tend to get hung up on "avoid turning to port"


AFAIK, there are only three sections in COLREGs which refer to this , none of which apply in this case.:


1. Power driven vessels in a head-on situation (14 (a)
2. Stand on power driven vessels when the other power driven vessel is not taking appropriate action (17(c))

2. Restricted visiblilty when detected by radar only (19 (d) (1)





(Interestingly, the only places that google found the phrase "turn to port, see you in court" are a few posts here and on the sister site "Trawlers Forum )

[Wotname]

Going back to basics - this is an exam question and as such it is presumed both vessels are acting in accordance with the colregs.

Therefore we implicitly know something about the range and speed of the other vessel.

Range is greater than 2 miles if it is a small sailing boat and hull speed will be less than about 10 kts. If it is a larger sailing boat, then both the range and speed be somewhat greater (I forget the numbers ATM).

The other vessel will have seen you and will be maintaining a constant watch on the situation. They will have also noted a constant relative bearing.

So once again, do I tack or fall off?

Tacking has risks and advantages as DH, StuM and Lode mention.
Falling off also resolves the collision aspect (IMO) but does not comply with Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel ".

Falling off far enough to show my stern light for say 30 secs and then coming back up to a beam reach will satisfy this requirement. It can't be interpreted as an overtaking situation. There is no situation where the other vessel seeing first red, then white and then red again could construe themselves as overtaking.

Falling off in the manner described also immediately creates an increase in range perhaps only small but coupled with a new heading(s), the collision risk is decreasing as soon as the manoeuvre is commenced.

[El Pinguino]

This is an exam question.... it should have a straightforward answer.... from the responses here it would appear that this is not the case....

The failing is that it just says that a light is seen on 'the port bow'.

It makes quite a difference where on the port bow the light is seen and the simplest way, once that is known is to do a basic ' how's she heading' calc... which you should be able to do, for all practical purposes, in your head.

Being an exam question a couple of quick assumptions can be made.... let us assume that the wind is from the north and we are close hauled steering north-east.

Now , lets say the light is on a steady bearing 4 points on the bow .. bearing North.
See first pic

So she can be heading from South anticlockwise through 112.5º (NB not 135º as stated somewhere above ) ... its a lot easier to work in points so that is 10 points....... So her heading is from South round to ENE...
Now if she is heading south she wont be on a steady bearing so it is safe to say that she is also on port and being the windward vessel should keep clear of you.

Now consider the case of a yacht showing green 2 points on the port bow.

She can be steering anywhere from SSW ( no risk of collision ) 10 points anticlockwise to East ( see 2nd pic) .... in this case you don't know what tack she is on so you are obliged to keep clear.

Relevant parts of Rule 12

'(ii) when both have the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward.

(iii) if a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on her port or starboard side, she shall keep out of the way of the other.'

So as the question does not tell us how many points on the bow the light is it follows that the question is flawed. (If this question was asked in orals that is the first thing I would ask the examiner to clarify.)

I think any candidate for an RYA ticket should be able to do 'How's she heading ' calcs and be able to work in 'points'.

[El Pinguino]

Another small point regarding bearing away or making any course alteration on a yacht in a collision situation..

If you are close hauled and you bear away you will have increased speed... if you are on a beam reach and come up onto the wind you will most probably see a reduction in speed ...the whole geometry of the thing alters... either for better of for worse....

[StuM]

Originally Posted by El Pinguino

Now , lets say the light is on a steady bearing 4 points on the bow .. bearing North.
See first pic

They said "On your port bow" not "broad on your port bow"

[El Pinguino]

Originally Posted by StuM

They said "On your port bow" not "broad on your port bow"

Pedantic semantics....... 4 points is the cut off between 'on the bow' and 'broad on the bow'..... a poorly worded question.

[Wotname]

I concur with StuM re port bow. It doesn't mean port quarter or port beam etc.

[StuM]

Originally Posted by El Pinguino

If you are close hauled and you bear away you will have increased speed...

And be pointing to a point further ahead of the other vessel.



IOW, you are still potentially on a collision course, you've just moved the likely point of impact further ahead of the other vessel.

[StuM]

Originally Posted by El Pinguino

Pedantic semantics....... 4 points is the cut off between 'on the bow' and 'broad on the bow'..... a poorly worded question.

No, four points is the cutoff between "on the bow" and "abeam"
Anything more than four points and it's not "on the bow" at all.

[El Pinguino]

Whatever... sigh...

You will speak of something being 5 points on the bow.... you will not say 3 points frd of the beam.... well most would not.

I chose 2 simple scenarios to help the OP understand the situation.... maybe I should have chosen three and a quarter points on the bow.... but I doubt many hereabouts can work in quarter points....

[Wotname]

Originally Posted by StuM

And be pointing to a point further ahead of the other vessel.



IOW, you are still potentially on a collision course, you've just moved the likely point of impact further ahead of the other vessel.

You can't be on a collision course if both your course and speed vector has changed. The other vessel hasn't altered its vector and you have altered yours.

There is only one solution of the two vectors for a collision to occur. Change one vector and that solution no longer exists.

Purely from a theoretical view of course (no pun intended).

[osprey877]

Originally Posted by dokondr

Agree, thanks, now I see..

I don't think so. If he is on your port bow and you can only see his starboard running light, then he could ONLY be on starboard tack if he was sailing by the lee or his port light was not working, both of which are very unlikely.

[osprey877]

Originally Posted by osprey877

I don't think so. If he is on your port bow and you can only see his starboard running light, then he could ONLY be on starboard tack if he was sailing by the lee or his port light was not working, both of which are very unlikely.

Oops. Disregard the above. Just saw the diagram with the boat fine on the port bow on starboard tack, so it is possible if, as somebody already pointed out, its within the 45 degree quadrant.

[Dockhead]

Originally Posted by Wotname

You can't be on a collision course if both your course and speed vector has changed. The other vessel hasn't altered its vector and you have altered yours.

There is only one solution of the two vectors for a collision to occur. Change one vector and that solution no longer exists.

Purely from a theoretical view of course (no pun intended).

I think you're making the same mistake some others have here -- any change in course or speed and you are no longer on a collision course.

This would be true only if both vessels were mathematical points, rather than bodies with dimensions, and only if you had perfect knowledge about the bearings between those points.

We actually discussed the issue of this uncertainty, in some depth, a few years ago.

What that means is that we can't be sure to get to a safe CPA by just changing any vector any amount, from what APPEARS to us to be a collision course.

But I agree with Ping of course that all this is way outside the scope of the exam question qua exam question.

[Wotname]

Originally Posted by Dockhead

I think you're making the same mistake some others have here -- any change in course or speed and you are no longer on a collision course.

This would be true only if both vessels were mathematical points, rather than bodies with dimensions, and only if you had perfect knowledge about the bearings between those points.

We actually discussed the issue of this uncertainty, in some depth, a few years ago.

What that means is that we can't be sure to get to a safe CPA by just changing any vector any amount, from what APPEARS to us to be a collision course.

But I agree with Ping of course that all this is way outside the scope of the exam question qua exam question.

I do agree that any small change in either course and/or speed may not create a sufficient CPA however I am seeing this as an exam question and we are given as a fact that the relative bearing is constant - there is no ambiguity here, unlike what might arise in real on water conditions.

Although not mentioned in the quoted post, my previous posts have described an initial heading change of ~70 degrees (from close hauled to broad reach- deep enough to show my stern light to the other vessel) before coming back up to a beam(ish) reach. i.e. still a course change of 45 degrees. This degree of course change coupled with the significant increase in speed achieved from falling off from being close hauled to reach would most surely provide a solution of an acceptable CPA.

Not saying by falling off to the degree I have described is the answer wanted by the RYA but I do suggest it would the satisfy the requirements imposed by the colregs - but as always, I am happy to be shown where my understanding is in error.