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Old 18-08-2017, 04:39   #1
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Collision Avoidance -- Dealing with Multiple Targets

I'm working on a guide to collision avoidance, and one of the subjects is dealing with multiple targets.

A crossing in open water with a single vessel cannot be that complicated. There will be one way to turn which will increase the CPA. Do it at the right time, and all is good.

But as we all know, sometimes you don't have complete freedom. One of those situations is when the one turn which increases CPA is an awkward one -- one which creates a green to green pass, for example, or one which requires a turn to port from an angle which is risky in case the other vessel turns to starboard. Another situation is when you are dealing with multiple targets at once.

Anyone have any good technique or insight to share? I can't say that I do anything especially ingenious myself. I try to figure out whether there is one turn which increases CPA to all targets at once (even if it's a 180). If not, then I try to figure out whether there is some turn which will create an acceptable CPA with all targets (which can be complex to figure out, but using OpenCPN and displaying the different position at CPA makes it a lot easier). OR, if TCPA is much different, then you can turn one way with respect to the closer target, then turn again.

It's much more complicated if you are stand-on with respect to any of the targets -- makes you wish you weren't. I have a guilty confession to make -- one time in the North Sea passing through a gaggle of ships going in different directions, I falsely raised a motoring cone, to give myself freedom of maneuver, when I was not actually entitled to it.

Dealing with multiple targets at once is also the classic case for needing to use the radio. To explain to one vessel that you will be doing such and such, because you've got another vessel somewhere you have to stay clear of, or to request some action by the stand-on vessel to help resolve such a situation, or to request a give-way vessel to hold course and speed.

Anyone have anything to add to this?
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Old 18-08-2017, 06:08   #2
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Re: Collision Avoidance -- Dealing with Multiple Targets

I am guessing that you are thinking of channel traffic near there UK. In the PNW , the rules are frequently set aside in deference to military security. A clear turn in whatever direction maintains the most clearance from those activities may not be enough to avoid an up close and personal encounter with escorting vessels. They will come to you.
There are many considerations. Tidal currents, rocks, commercial vessels and even other pleasure craft are thrown into disarray. Vessels under sail are viewed as erratic as they try to maintain some semblance of VMG toward their destination while being forced out of the way. Tempers flare as fishermen resist being moved off their preferred spot. I wish you the best and wish we could bring order to the mess.
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Old 18-08-2017, 06:42   #3
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Re: Collision Avoidance -- Dealing with Multiple Targets

My understanding is that the navigation rules are all based on two vessels crossing, overtaking or otherwise maneuvering in close proximity.

When a third vessel becomes involved, technically, all the crossing and overtaking rules do not apply. One is left to apply rule 2.
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Old 18-08-2017, 07:23   #4
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Re: Collision Avoidance -- Dealing with Multiple Targets

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My understanding is that the navigation rules are all based on two vessels crossing, overtaking or otherwise maneuvering in close proximity.

When a third vessel becomes involved, technically, all the crossing and overtaking rules do not apply. One is left to apply rule 2.
No, that's not quite correct. The steering and sailing rules continue to apply -- with respect to each crossing vessel individually. But Rule 2 allows you to deviate somewhat according to the necessities of the situation. And you apply Rule 2 to govern your actions when the other rules don't tell you what to do.
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Old 18-08-2017, 07:25   #5
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Re: Collision Avoidance -- Dealing with Multiple Targets

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Originally Posted by IdoraKeeper View Post
I am guessing that you are thinking of channel traffic near there UK. In the PNW , the rules are frequently set aside in deference to military security. A clear turn in whatever direction maintains the most clearance from those activities may not be enough to avoid an up close and personal encounter with escorting vessels. They will come to you.
There are many considerations. Tidal currents, rocks, commercial vessels and even other pleasure craft are thrown into disarray. Vessels under sail are viewed as erratic as they try to maintain some semblance of VMG toward their destination while being forced out of the way. Tempers flare as fishermen resist being moved off their preferred spot. I wish you the best and wish we could bring order to the mess.
I have no ambition to "bring order to the mess" -- I'm just trying to produce a handy guide for yachtsmen, which contains all of what is best practice.
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Old 18-08-2017, 07:36   #6
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Re: Collision Avoidance -- Dealing with Multiple Targets

I have a USCG unlimited radar endorsement on my license. This means that once every five years I have to go show that on a paper plotting sheet and on a radar simulator that I can do a two contact maneuver. This means I have to alter course, always to starboard, around two other vessels so as to pass at a specified closest point of approach (CPA). (Usually given by the "old man" in the standing night orders)

This works fine for ships who are going at speeds that are somewhat close to each other. 15 knots and 25 knots for example. But with sailboats versus a ship, 5 knots versus 25 knots for example, there can be so much difference in speed that there may be no solution for passing at a CPA of 2 miles for example.

So, get on the radio and make passing arrangements. I don't understand why so many people with pleasure boats are so resistant to do this. Professional mariners appreciate the contact. They live a mostly boring life on the bridge of a ship and appreciate the human contact from outside the vessel. I have been there, I know. They absolutely do not want to hit you....that is really bad for their licenses and their careers besides the more pressing goal of not wanting to kill anyone.

When you the stand on vessel starts changing your course, the ability for them to figure out your intentions is dramatically reduced. Being predictable for avoiding a collision is critical.

If you have AIS you will already know the name of the ship long before you can read the name on the hull, so you can say their name when you hail them on the radio which makes things much easier. A professional mariners ears will perk up when they hear the name of their vessel on the VHF. Being a sailing vessel you in all likelihood will be the stand on vessel. So be the stand on vessel and do not break the law by altering your course until it becomes apparent that they are not taking proper action to avoid a collision. If you cannot raise them on Ch 16 then try Ch 13.

Don't turn to port unless in extremis....make turning to port your absolute last option. When seeing you they 99% of the time, (like a good professional mariner), will turn to starboard. Turning to port will counter the proper turn to starboard that they made or soon will make.

With ARPA making a 2 mile (or whatever) CPA is a no brainer. So talk to them and let them do their turn to starboard to make their CPA, and you can continue sailing along safely.
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Old 18-08-2017, 08:16   #7
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Re: Collision Avoidance -- Dealing with Multiple Targets

What I mean is that for the sailboat itself, there may be no course alteration available for passing at a specified CPA. Besides, being the sailing vessel, you for most situations are the stand on vessel.
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Old 18-08-2017, 08:36   #8
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Re: Collision Avoidance -- Dealing with Multiple Targets

I agree with radio contact but this may not always be appropriate, where traffic control is heavily occupying the bandwidth (thinking of areas still in reach of Dover coast guards radio for instance).
I personally take an early course change and it most usually works fine (I do have AIS transponder so large vessels can interpret it early) and have seen several big ships (900' or more) slightly alterating theirs to allow me to continue.
Preventing any CPA shorter than safe being the primary goal, it happened I just hove to awaiting the large ships to pass safely. Stopping is also quite visible on the AIS.
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Old 18-08-2017, 08:47   #9
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Re: Collision Avoidance -- Dealing with Multiple Targets

If 16 and 13 are jammed then still stick to the COLREGS, always.

There is never a time or situation when the COLREG's are thrown out the window and it becomes a free for all. The COLREG's are internationally adopted law. I know there are some who think there are situations when the COLREGs do not apply....not true.
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Old 18-08-2017, 08:58   #10
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Re: Collision Avoidance -- Dealing with Multiple Targets

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If 16 and 13 are jammed then still stick to the COLREGS, always.

There is never a time or situation when the COLREG's are thrown out the window and it becomes a free for all. The COLREG's are internationally adopted law. I know there are some who think there are situations when the COLREGs do not apply....not true.
This is correct of course, and this thread is not really to discuss that.

I'm interested in specific tactics for multiple targets - the Rules don't give us a lot of guidance.
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Old 18-08-2017, 09:02   #11
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Re: Collision Avoidance -- Dealing with Multiple Targets

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Originally Posted by Dockhead View Post
I'm working on a guide to collision avoidance, and one of the subjects is dealing with multiple targets.
Why? The collregs are there to do exactly that and have been written as the standard for all mariners. If anyone has problems following them they need more training/experience.
I do agree that some of the situations in N. Europe get exceedingly complex hence the TSS's and small boat channels. If you have never sailed there it is hard to imagine but, as you know, a night entry to Portsmouth could involve a cruise ship, couple of container ships, some large military vessels under escort, several ferries crossing it all and a few HUNDRED pleasure boats, the channels are narrow with strong tides and some right angle bends just to add to the fun. It is a complement to the general standard of seamanship of everyone that there are not more incidents. My advice to anyone visiting such an area and not used to that level of traffic is to arrange for a local pilot, does not have to be commercial, most of these places have local yacht clubs and sailing schools that could put you in touch or supply a crew member with local knowledge. Will be well worth their expenses to lower your stress levels!!!

PS, I know Cowes, did my Yachtmaster assessment there
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Old 18-08-2017, 09:49   #12
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Re: Collision Avoidance -- Dealing with Multiple Targets

I agree multiple targets is a big complication (a bit like the three body problem and worse!).
An additional issue arises when there are not just multiple ships to be avoided but the ships have multiple small targets to avoid.
For example I have done three cross-channel trips this year with yacht rallies and we were very aware of the challenges presented to ships attempting (and succeeding, thankfully) in avoiding us.
As said on another post when it gets complex I agree that using the VHF can be a good move. Experience has shown that ships are happy to confirm what action they are or will take so everyone is confident of understanding.
I know some say that some ships don't respond on CH16 but on the one occasion, some years ago, when this happened to me a quick DSC call got an instant and helpful response.
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Old 18-08-2017, 10:14   #13
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Re: Collision Avoidance -- Dealing with Multiple Targets

Traffic types and conditions and actions can be different, tho the rules basically are the same.


the large commercial ships in our area :

San Pedro Channel : On catalina passages from the mainland of southern california those large commercial vessels are constrained to a traffic lanes and they are making mucho knots.

We have no electronic wonders, no radar, just our eyes and good sense.

1. Take a bearing on the large commercial vessel. If it is any where near a collision bearing we take early ample action and pass the ship on his stern. They are constrained to the traffic lane. We are a sailing vessel, lucky to be makng 5 or 6 kts. So, we make an obvious plan to pass astern.

2. The other large ship situations are in Long Beach and L.A. harbor. Especially at the narrow entrances at the jettys for both Long Beach and L.A. Harbor We stand clear . In the harbor anchorage area, we watch for any sign of those large ships underway, and making way. Or getting ready to make way. Avoid any possible problems ahead of time.

3. Been sailing out of Newport Bay, CA. for nearly 40 years, almost daily as an instructor and during the summer, you can have more than a thousand boats of various types to avoid, or they to a avoid you...

those are, several fleets of yacht club dingy races, mostly kids in sailing dingys, and same for fleets from different youth sailing organizations that are learning to sail and the instructor skiff is keeping an eye on his or her charges.

Then we have the sailing vessels, like me who are teaching lessons, plus , other sailing vessels heading out to see, or just day sailing in the harbor.

Add to that, the yacht club sanction sail boat regatta racing in the harbor on large and fast racing boats. These guys are very serious and think they are in the finals of the America's Cup. Not all that friendly to other vessel traffic.

Now comes the power boats. Booze cruisers, regular bay cruisers, salesmen doing demos, fishing vessels, commercial , and privately owned. Add in the large mega yachts of Newport, mostly with professional skippers. And the balboa ferry, all three of them crossing the harbor . Short distance.

And, the commercial charter tour boats, that do their constant newport harbor scenic cruises. Some of these are 100 toners. Oh , forgot, the 100 ton Catalina bound ferrys departing or returning to or from catalina.

And, also skippers like myself on revenue motor vessel bay and outside day charters, or heading to or returning from catalina.

Not done....toss in the small out board power boats, and small outboard rental boats, and the electric boats, and the wind surfers, oared Italian gondolas. etc.

And, we sail, and we are not looking at any eletronic anything or talking on the VHF, we go by collision bearings, thinking and planning ahead, rules of the road, and verbally exchanging what we are going to do with any conflicting vessel. These passes can be within a few feet or yards. And it is no big deal.

This is standard , for the summer, especially on summer weekends, but also during the week as well.

You have to have situational awareness all 360 degrees, not just on the bow.

I also plan ahead, since due to wind direction, we have to tack up the harbor to our slips at the very inner end. The distance from our slip to the channel entrance is about 3.2 nm.

We have to be aware of what traffic is overtaking as well, and not wait until the last minute to tack, and not be aware of several other vessels proceeding the same direction that will trap us against the boats in the slips. Gage their speed, and what their positions will be, and tack early and not get trapped and in irons , and bash into docks, boats or pilings.

Forgot, add in all types of vessels entering , leaving or standing off the gas docks. And the mooring fields constraining the boat traffice to just yards.

Now all of this is from memory , so I may have missed a few.

Wondering, if there is a section in the book for crowded , fairly narrow harbors, with all of the above situations .

We trained our members, they are sailing the 30 foot training vessels starting with their basic lessons on how to manage all of that undersail, We also advised them on how to mange all the traffic under power as well.

1. Constant 360 degree watch. Enlist the help of the crew, and add a bow watch, and a stern watch. But, the skipper also has to program in his mind a situational awareness for 360 degrees around his vessel. Always be thinking ahead, and what if.........I also look into the eyes of the helmsman of other vessels, does he even see our vessel

2. Rules of the road, sail to power, sail to sail, power to power. And maintain 100% alertness.

3. If necessary, make an early and ample change of course so the other skipper can see what your plan is. approaching dead on or nearly dead on, I will make a definite and ample turn, and then come back to a course that will take me clear of him. Most always it is a turn to starboard. Rules are to stay on your starboard side of a channel .Not everyone knows that, or follows that rule. So, we get those folks coming bow on , looking at the high end homes, and docked boats.

4. Don't be bashful about voicing your intentions. Just put "SKIPPER " , in front of what your have to say. keep in short and simple. Wake em up !

We have found, that many skippers of boats, sail and power, do not know the rules of the road, are not paying attention, an so the burden of avoiding collision falls on you.

5. Think ahead, plan ahead, and be ready for anything that may get thrown at you.

6. Have your crew, be ready to tack, or jibe, trim sails, and maneuver without delay.

7. Or , once in the harbor, motor your vessel the 3.2 miles to the club docks. Set a bow watch, and if enough people, a stern watch as well.

8. Make a good docking, Secure the vessel properly, and have a rum.

After all that, and recalling a normal day in Newport Harbor, I think it is time to splice the main brace .

To ya, lads and lasses.
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Old 18-08-2017, 10:34   #14
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Re: Collision Avoidance -- Dealing with Multiple Targets

I am with Roland here. To try to rewrite the C regs to suit all possible situations would need a super computer.How do you work out the scenario for a number of boats of different sizes travelling at different speeds at different headings in different wind and wave conditions? I worked on a salvage vessel based in Portsmouth harbour which required extremely strong watching keeping especially at night for a slow moving vessel. Our biggest problem was when sailing west past the Isle of White at night,you could be Stand on vessel one minute and then a large ferry travelling at 3 times our speed could suddenly appear from behind the Island with right of way at a mile distant. We would make a 90 deg turn to starboard and would after passing the stern of the ferry have to make a 180 deg turn to port followed by 90 deg starboard turn when clear of the Island, that is of course if other traffic permitted. To try and make up your own rules would create anarchy and no doubt would have given us a lot more work particularly in the Body recovery realm.
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Old 18-08-2017, 10:36   #15
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Re: Collision Avoidance -- Dealing with Multiple Targets

Simple guidelines, whatever you are going to do, do it early! Maximize the other vessel(s) opportunity to react. Secondly be predictable. Avoid multiple course changes whenever possible. Assume the other guy is half asleep and does not see you. Being right in a collision is lousy consolation.
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