Collision Avoidance -- Dealing with Multiple Targets

[El Pinguino]

Originally Posted by Dockhead

Did anyone say that? If someone did, I didn't notice it.....
I would also mention that if I had to choose between AIS and radar, I would keep the radar.

Actually if I were forced to choose between a chart plotter and radar, I would also choose to keep the radar.

I guess that shows what an old fart I am.

Its a bit of a mindset in ships large and small... new stuff = good stuff. Seen it with Transit SatNav... electronic DR assumed to be where you were... 'is electronic is good'. How many yachts did that put on reefs in the SW Pacific in the 70s/80s? Rather a lot I imagine.

Followed by GPS positions plotted on paper charts ( ignoring that lat/long was 2 lines and we had always been told to take 3 bearings with the third being a check bearing) ... the datum issue....

Then the 'Chart Plotter'! Same chart.... same datum issues ^^^^

And now AIS which some seem to think is god's gift....

I had to think about it but like yourself ... radar rather than AIS.

I view AIS as an early warning system when deep sea ....

[Dockhead]

Originally Posted by El Pinguino

Its a bit of a mindset in ships large and small... new stuff = good stuff. Seen it with Transit SatNav... electronic DR assumed to be where you were... 'is electronic is good'. How many yachts did that put on reefs in the SW Pacific in the 70s/80s? Rather a lot I imagine.

Followed by GPS positions plotted on paper charts ( ignoring that lat/long was 2 lines and we had always been told to take 3 bearings with the third being a check bearing) ... the datum issue....

Then the 'Chart Plotter'! Same chart.... same datum issues ^^^^

And now AIS which some seem to think is god's gift....

I had to think about it but like yourself ... radar rather than AIS.

I view AIS as an early warning system when deep sea ....

I totally agree that "new stuff = good stuff", but different "new stuff" is more or less revolution and more or less convenience.

Radar = revolution
GPS = revolution
Chart plotter = convenience
AIS = part revolution, part convenience

If I have a simple GPS (I used for many years an old Garmin wrist GPS made for runners) and decent radar set, I can do everything I do now with similar results. The plotter dramatically reduces workload and makes it easier to single hand in pilotage waters. AIS greatly reduces workload in collision avoidance, makes better data much more quickly available, and also makes it much easier to single hand.

Before GPS was a whole different ball game. We had LORAN on my Dad's old boat, but it was so clunky to use that we mostly did three point fixes and DR, and still hit the bricks from time to time (thank God for towing insurance ).

[ramblinrod]

Originally Posted by roland stockham

One thing I have not seen much mention of so far is AIS. Personally I have found it one of the most useful developments of the last few decades and would put it on a par with GPS as a safety aid. Yes like GPS there are issues with it and over reliance is one of them! In the same way that you get problems if people rely only on GPS and don't use radar, mark 1 eyeball and common sense you have problems. With AIS if you spend all your time looking at it and get into a 'virtual navigator' mode or assume that it make you visible to every one then you have a problem.
That said I think it contributes a few very important things to the mix in these complex situations. We can assume now that all large ships have AIS fitted and can confirm that by observing their signal (which is not the same as them looking at it!). If you have a transponder you also give them the same advantage. The big difference is that it also give an estimate of CPA which is faster and often I find more accurate than plotting with a compass. This allows better planning in complex situations. However I find the most useful information is that it shows rate of turn. Quite often it is hard to judge whether large ships are changing course by visual observation, you need to wait for their aspect to change. AIS tells you immediately that a target is responding to the situation by, say turning to starboard. I confirms they are taking action. I have been amazed to watch ships alter course by adegree or two at 10 miles out to adjust passing distances while they are still a dot on the horizon to me. Like GPS it takes a while to learn to get the best from AIS and maybe this is an area where we could develop some guidance for small boat sailors, whether new to sailing or new to AIS. I can thing of a few poor vis nights in the English Channel when I would have offered up my first born for such tech but then that was before we even had GPS but then again many people used to sail more cautiously, but that's another thread!!!

Wait a minute...You have personally witnessed large ships change course by only one degree from way out? Stop it! All the powers that be on this forum say that is not possible and simply won't work! Have all of these flawed maneuvers resulted in maritime tragedies like we've been warned here?

[ramblinrod]

Originally Posted by Pelagic

Another solution could also be to slowly turn away from the congestion , even back onto a reciprocal heading until the traffic clears so that you can return to your course.
This allows you to maintain control in strong currents and take further avoiding actions if necessary.

What we are discussing here are extreme conditions so i agree that stopping to wait out the congestion is a valid tactic

But not the only one!
....keep in mind that a vessel underway but not making way, still has an obligation to avoid a collision under the rules

Slowly turning away from congestion is a solution (if it can work). Turning to a 180 degree course is a solution (if it can work). I stated that if there is NO solution the only appropriate course of action is to sound 5 short blasts and stop; there is simply nothing left to do, other than display a "not in command" or "at anchor" symbol (in which case, others will need to do same if they have no solution).

[roland stockham]

Originally Posted by bmz

I agree with you; AIS is a godsend for collision avoidance. However, I have a problem with clutter on AIS; sometimes I have a half a dozen or more collision intercepts showing on my chartplotter (I don't want binnacle clutter either).

I have long since turned off my audible alarms. The technique I have found most successful is to focus on the class A intercepts, and ignore the class B until they are within a couple hundred feet of my vessel. But I have gotten a lot of negative feedback over that.

What you do about AIS clutter?

To clarify; When I talked about watching ships adjust course by a very small amount this was on passage in the Caribbean sea. I had just fitted a transponder and was on passage from Aruba to Panama and was surprised to see ships making very small adjustments at 10-15m out so as to increase clearing to pass 2m off. The course changes are not visible by any direct observation including radar but did show up on AIS. It was a nice confirmation that the system works! Clutter was not an issue as it was rare to have more than 1 ship per day within range. Once close to Panama I found it best to close the range down to 3 to 5 miles to avoid clutter. Generally in the canal zone everything is channeled into lanes and you don't have a melee of small craft and ferries to worry about but the ability of AIS to look down a channel and sea a ship coming round a bend was very useful on the rare occasion I did need to cross a lane. So far I have found AIS to be very good in combination with radar because it give a more accurat course and speed and shows rate of turn. I also find that it does no suffer from as many false cause by radar being reflected of waves and AIS will pick up a target at much greater range (80m is my current record!!).