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-   -   Collision Avoidance, Cones of Uncertainty, and Appropriate CPA (https://www.cruisersforum.com/forums/f90/collision-avoidance-cones-of-uncertainty-and-appropriate-cpa-189919.html)

El Pinguino 23-08-2017 19:34

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by barnakiel (Post 2462677)
....
A sailing boat is supposedly the one with the right of way (over a steamer). Most of the time.
.........

Cheers,
b.

Given that the only 'steamers' you are going to see these days are merkin aircraft carriers and SSNs ( and you won't be seeing them ) I wouldn't be pushing my luck :biggrin:

ramblinrod 23-08-2017 19:35

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by StuM (Post 2462762)
It's actually set out in COLREGs.

Rule 7 - Risk of Collision
...such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change


Yup, when you operate a small boat, collision avoidance is not that difficult if one simply keeps watch, stands on, gives way, and applies some common sense as required.

The is no math to do, no cones of silence required. Just don't f' around in the shipping lanes and you'll be fine.

Most intelligent sailors don't run up the centre of a shipping lane, route, or course head on. When one is crossing a ships course, at right angles (as they should), turning off a little bit from 5 nm away is more than ample. If in the event one miscalculates, just luff up until you can safely pass astern. And yes, there is absolutely no reason to pass a full mile astern. You can if you wish, and it is safe to do so, but a full mile certainly isn't necessary.

David M 23-08-2017 20:59

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
This is why the Rules say "early" and "apparent" action to avoid a collision. You don't even have to know second-grade addition in order to comply with early and apparent.

If you get to the point of an imminent collision, you have already broken at least one rule.

Apparent means very obvious to the other vessel. One degree of course change....bad. 30 degrees of course change....good.

Jim Cate 23-08-2017 23:22

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Most intelligent sailors don't run up the centre of a shipping lane, route, or course head on.
True, of course, but there are places where meeting ships on near reciprocal courses is fairly common, and that do not meet your classification.

EG, up and down the east coast of Australia. Not as busy as the English Channel, but with significant ship traffic, some N bound, some S bound and some peeling off for destinations to the East. There are no designated "shipping lanes", no TSS spots, and one finds ships at varying distances from the coast, going both ways. And it isn't always a matter of avoiding just one, nor of the conflicting ships all being going the same way. When you are caught in the middle of a pair of N and a pair of S bound ships, it isn't all that simple to calculate how to dodge them all, so standing on as required by COLREGS seems a good practice, especially if you are broadcasting AIS info.

Life here has been much better since I installed AIS 1

Jim

conachair 23-08-2017 23:39

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2462823)
Yup, when you operate a small boat, collision avoidance is not that difficult if one simply keeps watch, stands on, gives way, and applies some common sense as required.

The is no math to do, no cones of silence required. Just don't f' around in the shipping lanes and you'll be fine.

Most intelligent sailors don't run up the centre of a shipping lane, route, or course head on. When one is crossing a ships course, at right angles (as they should), turning off a little bit from 5 nm away is more than ample. If in the event one miscalculates, just luff up until you can safely pass astern. And yes, there is absolutely no reason to pass a full mile astern. You can if you wish, and it is safe to do so, but a full mile certainly isn't necessary.

easy peasy ;)

https://youtu.be/pzJwXxUY3MM

BTW, ships will often have standing orders for no CPA less than 1 mile so you being getting battered by the wash tucked in to their stern will freak them out a bit, not a very nice thing to do. In the channel anyway, with the miracle of ais it's common to have them manoeuvre to give you exactly 1nm CPA, which is you crossing thier bows maybe 3nm ahead.




What happened to the add video button?

bobgarrett 24-08-2017 01:18

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Some excellent thoughts on this topic, and we all must bear in mind that ship collisions are rare.
But why is that? Because of the colregs and the professional application of them.
Like others I will look at handheld compass bearings as well as AIS. However, those who think they have avoided a low CPA by a minor course correction might learn otherwise if they had also watched their AIS and seen a ROT figure for the ship a few miles away. I would contend that it may well have been the ship that avoided the collision not you.

StuM 24-08-2017 01:20

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Jim Cate (Post 2462910)
True, of course, but there are places where meeting ships on near reciprocal courses is fairly common, and that do not meet your classification.

EG, up and down the east coast of Australia. Not as busy as the English Channel, but with significant ship traffic, some N bound, some S bound and some peeling off for destinations to the East. There are no designated "shipping lanes", no TSS spots, and one finds ships at varying distances from the coast, going both ways. And it isn't always a matter of avoiding just one, nor of the conflicting ships all being going the same way. When you are caught in the middle of a pair of N and a pair of S bound ships, it isn't all that simple to calculate how to dodge them all, so standing on as required by COLREGS seems a good practice, especially if you are broadcasting AIS info.

Life here has been much better since I installed AIS 1

Jim

Generally, I find the problems occur when they peel off to destinations to the West (i.e they are heading in to Gladstone, Rockhampton, Mackay,Townsville etc while I'm transiting North or South and holding just inshore of the two way routes) :)

four winds 24-08-2017 01:39

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I've crossed with big ships offshore maybe about a dozen times only. Two in the last week while coming back up to AL from FL.

On a good night I can see the glow off the deck lights before the ship appears. And begin noticing the bearing then. A few times I have been able to notice thier course change from a constant bearing. How did they know I was under sail, maybe my speed. Maybe they eventually see my lights showing sailing. I don't know.

But my hat's off to the professional mariners out there. I feel comfortable saying that each time they passed one or two miles ahead or astern.

I do my part, I stand on. And they appreciate it. Once, a skipper hailed and said, "Hey sailboat, thanks for being a stand-up stand on sailor". I called back, "Your welcome cap, ..... wait, there's a boat out there! ..(slight pause, big laugh)... gotcha!, have a good night".

I've never had to alter course for a big ship offshore.

Alan Mighty 24-08-2017 01:56

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by StuM (Post 2462928)
Generally, I find the problems occur when they peel off to destinations to the West (i.e they are heading in to Gladstone, Rockhampton, Mackay,Townsville etc while I'm transiting North or South and holding just inshore of the two way routes) :)

I've found that Gladstone Harbour and Brisbane Harbour give excellent service to yachties. Gladstone Harbour requires (or used to) yachties to log in with them by VHF. In Moreton Bay, Brisbane Harbour on VHF12 gives clear info on traffic and in the past has delivered good service disciplining both commercial and recreational traffic.

See the AIS heat map from marinetraffic dot com: E Aus Coast heat map.gif

Alan Mighty 24-08-2017 02:02

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
The AIS heat map around your waters, StuM, looks pretty impressive too.

rramsey 24-08-2017 03:00

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
There's another thread on the recent collision of a USN vessel (US Navy Destroyer Collision Again!!!) that might be of interest to this discussion.

As I understand it, USN vessels often run "dark", e.g. no way to pinpoint them. No radar, I presume, no AIS. I am not sure if that means no receiving AIS because that too might be detectable. This means that the sole responsibility for avoiding collisions rests on the USN vessel. We probably should assume that the crew is highly trained and very professional and yet collisions seem to happen. Assuming they run dark, the other vessel involved has no way of avoiding the collision as it is not aware in any way that there is a USN vessel crossing their bow.

That (maybe) being the case it shows that avoiding collisions is best done by all vessels involved and that it is also up to us, as WAFI's, to do our part. Being slow and small, I think the best we can do is, to be abundantly clear about our intentions (e.g. don't suddenly change course if not absolutely necessary) and radio in. I have been told by captains of large vessels that they anticipate well in advance and change course if required. They hate WAFI's then changing course (in the false belief that that avoids collision) without need or communication, thereby bringing themselves back into the path that leads to recreational antifouling getting a sun tan.

Abundantantly clear, to me, means anticipate well in advance, 5nm is probably reasonable (as it is 10 to 15 minutes to CPA for large vessels), make your move and stick to it. If the large vessel changes course and brings you in danger, get on the radio immediately to co÷rdinate a safe solution.You have only minutes to avoid a collision.

Maybe a silly remark, but still: if in doubt, aim for the other vessel. By the time you get there it will be long gone (unless it is anchored of course, in which case you're gonna look as silly as a baboon for sinking your yacht). Don't keep aiming for it, of course, aim once and stick to your course.

ps. Have also seen 30ft yachts trying to sink a 300mtr container ship. Unsung heroes of our messed-up gene pool :trash:

rabbi 24-08-2017 03:01

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
AIS is a wonderful thing. not always.
Standing on is a wonderful thing. not always.

AIS plus standing on can be dangerous.


When we first added an active AIS to our boat I expected that this would make us more visible and give clear info on our course to all big ships out there. So standing on would be more prudent than altering course to avoid close encounters, which we did before.

Didn't really work out well: On our first night passage after adidng AIS we were sailing between Italy and greece, with lights on, broadcasting our AIS position. We have been passed very close by a huge container ship and a cruise ship.

CPA was around 300m but felt much closer (no clue if the antenna position was part of the calculation). Not a problem for them but frightening for us.
I bet without AIS they would have stayed clear, but AIS told them we are safe so they just kept course.

If huge ships are passing us with 30kn there is not much we can do, especially not if we stand on until the last moment. Now we alter course early and significantly enough for them to notice, and/or we hail them on VHF.
Just what we did before we had AIS.

Dockhead 24-08-2017 03:28

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2462823)
Yup, when you operate a small boat, collision avoidance is not that difficult if one simply keeps watch, stands on, gives way, and applies some common sense as required.

The is no math to do, no cones of silence required. Just don't f' around in the shipping lanes and you'll be fine.

Most intelligent sailors don't run up the centre of a shipping lane, route, or course head on. When one is crossing a ships course, at right angles (as they should), turning off a little bit from 5 nm away is more than ample. If in the event one miscalculates, just luff up until you can safely pass astern. And yes, there is absolutely no reason to pass a full mile astern. You can if you wish, and it is safe to do so, but a full mile certainly isn't necessary.

And this, on the other hand, I agree with completely.

I've written it many times on here -- if you are sailing in harbors or bays or approaches to harbors, then you have a huge advantage compared to sailing in open water -- you know where the ship is going to be. All you have to do is stay out of the channel or fairway until he is safely past. This makes all other collision avoidance techniques unnecessary.

And yes, passing behind by a couple of cables can be fine, when you're crossing a fairway or channel and it is clear you will actually pass behind.


The only thing wrong is projecting this formula onto an entirely different situation -- a crossing in open water. The problem is that in open water, unlike in pilotage waters where the commercial traffic is following defined fairways or channels, you cannot know exactly where he will be 10 minutes from now. It was said in another thread, something like "You don't have to be a mile away, you just have to avoid being in the exact same place as he is -- it's easy." The problem is -- what is this "exact same place"? You don't know and can't know. "Just alter course by one degree at five miles and you'll be fine -- 180 feet is enough space." I hope it's now clear why this doesn't work.

rramsey 24-08-2017 03:29

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by rabbi (Post 2462945)
AIS is a wonderful thing. not always.
Standing on is a wonderful thing. not always.

AIS plus standing on can be dangerous.


When we first added an active AIS to our boat I expected that this would make us more visible and give clear info on our course to all big ships out there. So standing on would be more prudent than altering course to avoid close encounters, which we did before.

Didn't really work out well: On our first night passage after adidng AIS we were sailing between Italy and greece, with lights on, broadcasting our AIS position. We have been passed very close by a huge container ship and a cruise ship.

CPA was around 300m but felt much closer (no clue if the antenna position was part of the calculation). Not a problem for them but frightening for us.
I bet without AIS they would have stayed clear, but AIS told them we are safe so they just kept course.

If huge ships are passing us with 30kn there is not much we can do, especially not if we stand on until the last moment. Now we alter course early and significantly enough for them to notice, and/or we hail them on VHF.
Just what we did before we had AIS.

You're probably right ... AIS should not change our behavior. It just means you and they see things sooner.

Pelagic 24-08-2017 03:36

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Many here are over thinking the issue of how much for course change ....and trying to create a one fits all guideline.

Firstly COLREGS recommends a course change that is sufficient and READILY APPARENT TO THE OTHER VESSELS.

That makes sense and a simple technicque I employ at night when making a decision to alter course is to OVEREMPHASIZE the course change at fist.

That often results in a change in the running lights they see from me, which I hold for about 5 minutes if sea room allows, so they know my intentions.

I also do that during daylight

Then I bring back course to an appropriate CPA.

Appropriate CPA is really dependant on sea room.

If you have lots of sea room, what is to be gained from being inside 1nm CPA. ...??

Masters give standing orders of calling them to the bridge inside 1 nm CPA.... to make sure they are not disturbed with stupid stuff.

So why not in a passing situation simultaneously adjust so that both captains can get some rest?

Obviously in a limiting channel 1nm is not practical and the captain should be assisting the watch keeper.

Hope all that makes sense.


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