Old WNS thread - was the 'expert' right? (long post)

[timbartlett]

Re Mapis M
I know it's considered clever to disparage anything wikipedia says, but it's a lot easier to cut and paste from http://en.wikipedia.org/wiki/SS_Andrea_Doria than to type out the same essential facts from any of the countless printed references available:-

The original inquiry established that in the critical minutes before the collision, Andrea Doria gradually steered to port, attempting a starboard-to-starboard passing, while Stockholm turned about 20 degrees to its starboard, an action intended to widen the passing distance of a port-to-port passing. In fact, they were actually steering towards each other — narrowing, rather than widening, the passing distance. Compounded by the extremely thick fog that enveloped the Doria as the ships approached each other, the ships were quite close by the time visual contact had been established. By then, the crews realized that they were on a collision course, but despite last-minute maneuvers, they were unable to avoid the collision.

In the last moments before impact, Stockholm turned hard to the starboard and was in the process of reversing its propellers attempting to stop. The Doria, remaining at its cruising speed of almost 22 knots (41 km/h) engaged in a hard turn to port, its Captain hoping to outrun the collision. At approximately 11:10 PM, the two ships collided.

 

[hlb]

So, to recap. It is a bright clear day. We see that we are on a colision course with a super tanker from some miles away. We are the stand on vessel. We have many choices of action, except turning to port . How ever Col regs says. We must hold our course and speed!!

We are aware that the super tanker can not stop within 12 miles and can not turn very fast.

So we must carry on knowing that the super tanker is not going to change course one inch.

Just before we tw#t the super tanker, we are now allowed to turn to port. Whether this is three feet away, thirty yards, or half a mile, is unclear.

Right. I think I've got it now.

 

[jhr]

Haydn,

Surely none of this applies to you anyway, 'cos you're on autopilot?

 

[jimg]

Haydn,

Surely none of this applies to you anyway, 'cos you're on autopilot?

Ah, but he has got a <-- button to press!!

 

[hlb]

Haydn,

Surely none of this applies to you anyway, 'cos you're on autopilot?

I know none of it applies to me. I decided that I was not going to whats it's name anyway, but going to thingamijig instead. You know. That place just behind the super tanker.

 

[RIB_imposter]

6. Rule 7d(ii) is absurdly worded and has no basis in the laws of physics

Nothing absurd about it. Large vessel (and/or tow) relatively close. Lets say it occupies 15 degrees of you "field of vision". If a fixed point on that vessel remains at the same compass bearing you are on a collision course. But if it moves by 10 degrees (an appreciable amount) are you going to "clear it"? Not necessarily you may just smack the stern rather than the bow.

HLB - I think I understand what you are saying - by making a small adjustment to course early you are preempting the existence of a collision situation and therefore avoiding having to apply the specific rules for a collision. However a 3deg change at 1 nm only puts you <100m to port of where you would be. Is that enough to pass safely? Is it enough for the watchkeeper on the ship to know you will pass safely?

 

[hlb]

However a 3deg change at 1 nm only puts you <100m to port of where you would be. Is that enough to pass safely? Is it enough for the watchkeeper on the ship to know you will pass safely?

--------------------------------------------------------------------------------

Yep I know. I'd radio'd the ship to chuck me a box of matches down as I passed.

 

[jfm]

Nothing absurd about it. Large vessel (and/or tow) relatively close. Lets say it occupies 15 degrees of you "field of vision". If a fixed point on that vessel remains at the same compass bearing you are on a collision course. But if it moves by 10 degrees (an appreciable amount) are you going to "clear it"? Not necessarily you may just smack the stern rather than the bow.

The point you eventually hit - the stern in your example - MUST be on a constant bearing to you, else you will not hit it. That's just basic geometry.

When looking at the vessel that subtends 15degrees (ie a scarily close vessel or a more distant long tow), it is important for us as helmsman to observe whether there is ANY point along the length of the "target" boat whose bearing doesn't alter. That's the exact point you'll collide with. When looking at a long tow, dont be duped by the fact the bow is changing bearing. Check the stern too. If they're both changing bearing the same way, you'll miss the whole thing. If the bow is changing bearing in opposite direction to stern, you'll hit it somewhere in the miiddle

It is geometrically not possible for all points along the target boat to change bearing and for you still to hit it. If you're going to hit it, the part you'll hit is on a constant bearing

This is much more relevant to a long tow. If another boat is subtending 15degrees of your view you're way too close and need to do something urgent and not muck about observing its bearings. A 100m boat that subtends 15degrees is only 380m away from you, 45 seconds from impact at 20kts, sheesh! In practice, you are nearly always taking collision avoidance deciscions when the other boat subtends say <5% in your field of view

This is not the most serious bit of lousy Colregs drafting - far from it

 

[benjenbav]

It is geometrically not possible for all points along the target boat to change bearing and for you still to hit it.

unless you are on a curving trajectory yourself when all points on the target will constantly change up to the point of intersection (aka the crash site). eg a gradual but constant turn to port.

 

[RIB_imposter]

It is geometrically not possible for all points along the target boat to change bearing and for you still to hit it. If you're going to hit it, the part you'll hit is on a constant bearing

OK mathematically you are correct. But the key word in the colregs is "appreciable" which I take to be about "perception" rather than physical fact. They could say "neither the bow nor stern, both changing in same direction" etc as you did - but they are wordy enough as it is. If the other vessel is changing course or speed then again it may create a perception of change in angle which is not going to clear you. I think they are really saying "my compass bearing said we will miss each other" is not a defence!

 

[jfm]

unless you are on a curving trajectory yourself when all points on the target will constantly change up to the point of intersection (aka the crash site). eg a gradual but constant turn to port.

Yeah sure. Likewise if t'other boat is turning. Or eaither boat is not constant speed. The only point I'm making is that Colregs is badly written on this point. I don't think what you say (which is perfectly correct) exonerates the Colregs draftsman (does it?)

 

[jfm]

OK mathematically you are correct. But the key word in the colregs is "appreciable" which I take to be about "perception" rather than physical fact. They could say "neither the bow nor stern, both changing in same direction" etc as you did - but they are wordy enough as it is. If the other vessel is changing course or speed then again it may create a perception of change in angle which is not going to clear you. I think they are really saying "my compass bearing said we will miss each other" is not a defence!

No worries, I think we agree the trigonometry! I remain of the view that 7dii is lousily drafted, though other parts are worse. If you consider that 7dii is well drafted, let's just agree to differ

Anyways, while looking at the flashing yellow light thread I checked something in the lights part of the regs. Check out the draftsmanship in Rule 20b. The first "or" should unquestionable be "and" (or a comma). The second "or" is ok. The third "or" should be "and do not". This is unquestionable. Getting "and" and "or" mixed up is a pretty big screw up. The drafting is just terrible, and each time you read them you see more mistakes.

 

[benjenbav]

As you know, I'm only pulling your leg.

R7(d)(ii) would be clearer if it read [addition in italics]:

"Such risk may sometimes exist even when an appreciable bearing change (referenced to a fixed point on the other vessel) is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range."

or by way of reductio ad absurdum:

"If you're really close or the other vessel is really big the fact that bits of it appear to be sliding away from you doesn't mean you'll miss it entirely."

 

[benjenbav]

Getting "and" and "or" mixed up is a pretty big screw up.

Pre-emptive strike coming up here:

PLEASE no-one suggest "and/or".

As one of my colleagues is fond of saying, "If you can find this formulation in Shakespeare, let me know and I'll start using it."

 

[jfm]

As you know, I'm only pulling your leg.

R7(d)(ii) would be clearer if it read [addition in italics]:

"Such risk may sometimes exist even when an appreciable bearing change (referenced to a fixed point on the other vessel) is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range."

or by way of reductio ad absurdum:

"If you're really close or the other vessel is really big the fact that bits of it appear to be sliding away from you doesn't mean you'll miss it entirely."

I know you're pulling my leg . What you write brings us to the philosophical point that the Colregs are unclear as to whether they're just rules or whether they're hints and tips on how to drive a boat. The paragraph you've drafted is a hint and tip, not a rule. To make it a rule it has to be something like "The watchkeeper shall take into account that such risk may sometimes exist even where...", but of course that's still a hint and tip dressed up as a rule. There's no point in having a rule that requires you merely to think about something, cos it'll never be provable that the accused didn't think about it. So you might as well scrap the whole thing. I still say the Colregs are terribly drafted and we all get by without smashing our boats cos we're sensible folk who can work it out for ourselves. But it's not very satisfactory when you get bg ships smashing into each other. They need a re-write, BJB! We could do it on this forum

 

[hlb]

We could do it on this forum

Yep, I can see it now. If the raggies are involved, there will be thousands of rules, all excluding them.

If Tim Bartlett is involved......... Well I suppose super tankers can only stand so much bashing, even with little boats.

I'd make all ships go clockwise round the world, then they cant bump into each other. Problem solved.

 

[MapisM]

Re Mapis M
I know it's considered clever to disparage anything wikipedia says, but...

Don't worry, since I pretend to be clever, I neither wish to disparage wikipedia just to be considered clever, nor I need to read it to know what I'm talking about.
And yes, I did say that I would have refrained from commenting further.
Besides, trust me if I tell you that these days, in spite of this longish post I'm now typing, I have very little time for these debates, and I can only have a look at this hour, ar the expense of some overdue sleep.

BUT, you're forcing me to clarify a couple of things.

Firstly, the collision we're talking about.
Secondly, why I came to the conclusion (even before this last post of yours) that hlb was spot on when he said that, reading your posts, "if you aint got a clue, teach" is what springs to mind.

Re. the collision, in a nutshell, the real, sad story is as follows:
On one hand, an extremely experienced captain did exactly what any other experienced captain would have done - A to Z.
Otoh, a third officer in his mid twenties made a huge evaluation mistake, and acted (respecting colregs!) accordingly, even when it became obvious that he should have changed his course of actions to avoid a disaster.
Mind, the above is nowadays considered a fact, even in the wikipedia page you're quoting, if you just take the time to scroll down further instead of quoting just the "original inquiry". Though I'm sure you already did.

Re. clueless, you might have noticed that I didn't reply to your post #37, where you carefully picked some pieces of truth, extrapolating them from their context, to support your viewpoint.
That's the typical approach of people who would rather deny or try to revert even the most obvious evidence, than admit to have possibly said something slightly wrong.
Fair enough I thought, each to their own. And I decided to bow out of what was becoming a boring academic debate.
But obviously you must have been strenghtened by my silence, 'cause you felt the need in your post #44 to make that pointless comment I had to reply to. And now again with wikipedia, you're picking one statement out of a context just to support your own opinion, regardless of the truth.
Besides, mind, I'm sure you're perfectly aware of that.
Now, sorry, but after dealing for decades with these behaviours on a daily basis, I'm now fed up enough to not stand them anymore in real life - let alone in a forum.
So, feel free to further bash or distort anything I said.
Rest assured that I won't waste one more minute on this or other similarly useless posts of yours.
Nice night.