A wild assed guess is not the way to sink these ships.
There is a good way, depending on what they are actually doing
First, we have to decide what you mean by zig zag
In the first instance, a ship or convoy will typically travel 10-20nm in one direction, then they will all turn to a new bearing for another 10-20nm
In this case observation and planning will put you in a good attack position.
However, I do not think you are talking about this case.
I think you are talking about the case when you have the convoys bearing and speed figured out, and the they panic and go slightly mad.
In this case, they do not zig zag as such, they do something called constant helming.
This looks like a nightmare to target, because the AOB is constantly changing.
But if you remember a few things, you can consistently get good hits in.
In the below example the red line is what you see the enemy ship doing.
See anything interesting about this diagram?
Excuse the poor paint image, it is late and I have had a few beers
The red line is what you see the Japanese ship doing, but -
and this is the key - he is doing it along a base course.
Treat this like any other target, and start plotting again.
For example, I would plot the following, over about 5 minutes
The three minute rule still applies in this case, because rather than trying to find out the ships absolute speed, you are trying to find out its speed
along its base course.
Although to be honest with you, I would rather plot it for 5-10 minutes and use the nomograph to get the speed. In this situstion using just 3 minutes could be a bit unreliable!
It will take a bit longer than usual for a good solution (I go for 5-10 minutes), but treating the ship as if it is travelling along the base course will usually give you a pretty good solution.
Special Case
What do I do if I am just about to fire and they get freaky?
This has happened to me so many times
The Japanese ship is just about to cross my periscope and something freaks them out and they start constant helming. Either the ship sees my periscope, or one of the escorts detects me.
I have come up with a good rule of thumb for these circumstances.
Keep your
AOB/enemy ship course the same, and make your solution speed 2/3 of what it was before they freaked out.
I use this a lot, and get hits more often that I get misses.
Hope this helps
