Prayer to bona alma:
- correct the post 4 with the correction from the post 5
- delete in the post 4 remarks that are not necessary anymore
- delete the post 5
- delete this post
...and pray with me that bmad concedes it is the Best Answer

Correction: B sends: - if(measurement<4) measurement else 7-measurement. P.S. It would not be bad if the table in my previous post magically appeared in a fixed font.

We know that A sees B=334 and c=334 - A CANNOT see B=335 and C=334.
(Not to confound with: "As this information in not available to him, he ASSUMES he has 334 or 335.")
So my first answer was correct. In the 2nd try, I got lost and could not correct quickly enough.

I like the Phil1882 idea of modulo and tried the following rule:
It works for some examples for N=4 (with no counterexample so far). The next steps should be an exhaustive computer simulation and a strong therie. Someone is willing to continue?

They can follow other than mirror paths to meet at the same point.
If they meet, they meet at the diagonal. The probability (for each one) to get to a particular point on the diagonal is:
Pascal's triangle/(2 power n).
I hope someone finds a formula for the product.

If I posted this problem, I would ask to clarify:
1) why the lines H and I cannot be parallel;
2) crossing trajectories do not necessarily imply that the ships collide.
BTW, the sea should be endless (so that H does not reach her destination before colliding).

You got the first part to 97% - I wanted to hear "section of a pipeline along the trajectory". The tank of the U.S. scenario corresponds quite well to the pipeline, just the section of a tank is not measured in 1/m2, so the second part of the problem is still open.