The coordinates could be worked out by looking at Hoban’s map in the map room, the 'X's on the map represented where the ship was at each time (six x's, six times). The arrow is the direction that the ship is moving, thus each x is a step further in time. I can't remember if it was letters or numbers on the x or y plane, but only one of those ways worked for the given coordinates. If you figured that he fell at 6:00, then he must have been at the 6th x, with those coordinates you're set.

Although I half guessed on the location on the ship, it is known that Orrin saw him fall from his porthole in the stockroom; whatever was above that porthole must have been where Hoban fell.

Hope that helps!