[QUOTE=tomoose;1447592]reference (degrees).
The sub/ship is zipping along on a heading of 315 degrees (relative to north). A crew member yells out, "ship spotted, 090 degrees!". The crew instinctively look 90 degrees to the right of the centerline of the boat.
I quoted the portion of tomoose's post that I think will help you the most.
When the lookout says 90 degrees, he is telling you that he has spotted a ship at 90 degrees from the center of the his boat. The lookout does not know the course as he is looking though his binoculars while on duty in the conning tower. But he does know the the target's relative position to his boat, because he knows the bow of his own boat is always deemed to be pointing at at 0 degrees. The lookout is saying, "I do not know what true course our boat is heading, but at 90 degrees from our sub I have spotted a possible target." The possible target that he has spotted is at a position 90 degrees relative to his boat. That is its relative bearing. Why is it called "relative" bearing? Because it is determined in reference to the direction of our boat, which, without considering our boat's true direction (course), is deemed to be zero degrees.
Target's true bearing: We know from the map that the true course of your boat boat is 315 degrees. That is its direction in relation to true north. (Look at the map and confirm this.) However, we do not know any information about the true course of the target, as it could be moving towards your boat, parallel to it, or away from it. To figure out the true course of the target, you have to plot the target's course over time using the pencil tool, and then use the compass tool to determine its course. It the target's course is parallel to your boat, its true course would be 315 degrees also, but its longitude and latitude would be slightly different.
Got it?