They must be on the two ends of the ship..And the ship is sailing east to west (or west to east)..
--->looks east <-----looks west
------> ship sailing west to east.
isn't it ?
The marines are standing on opposite SIDES of the ship, not ends!
Hence they need to be sailing anywhere BUT east to west or vice versa!
Pick any two points on opposite sides of the ship and draw a line between them.
Now put that line on the east/west axis.
Providing that there is room for these marines to see each other, they could be travelling in almost any direction!
Sorry, wrong. Your solution is fine, but you shouldn't have corrected mannu. His is correct because there is no definate "side" of the ship. If you want to be technical then the ends are just another side of the ship, only pointier. Although, it doesn't really matter which direction the ship is going because if one were halfway between the front tip and the right middle while the other was halfway between the back tip and the left corner, then if the ship was going north-east they would still be able to see each other. If I'm COMPLETELY wrong about correcting you, I appologize greatly. It is 3:35 A.M. here. So, I am a bit tired since I got up at 7:00 A.M. yesterday morning.