The bow on a ship or boat is the front part of the vessel and the front part of the bow, or point of the bow, indicates the direction the vessel is heading or its bearing. A change in direction is indicated by the points of a compass which are measured in degrees, like the 360 degrees of a circle, 0 degrees being directly north. When the question was asked, "Bearing?", the answer came back, "three degrees on either bow", meaning no more than three degrees to the right or to the left. The vessel was heading at 139 degrees on the compass, so three degrees to the left (port) would be 136 degrees, and to the right (starboard) would be 142 degrees.