Collision Avoidance -- Dealing with Multiple Targets

[Dockhead]

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?