Calendar: Events NPS Press Room What to Visit: USS Pampanito Balclutha C.A. Thayer Eureka Alma Hercules Eppleton Hall Small Craft Visitor Center Museum Library How to Visit: Directions & Hours Pampanito Tickets Online Education Programs Facility Rentals Maps Membership Join Us Donate About Us: Join Us! Donate Volunteer Wish List Contact Us Publications History Trustees Bylaws(pdf) Financial(pdf) Jobs Search Maritime.org
 2 BEARINGS: RELATIVE AND TRUE A bearing is a number which tells the direction of another ship or object. A lookout gets bearings by sight, a conning officer by looking through the periscope, a sonar operator by listening through his gear. After contact is made with a target, the sonar operator keeps reporting bearings continually. Therefore, he has to know what bearings are, and how to read and report them. Relative Bearings Usually a sonar operator reports relative bearings because they tell direction in relation to own ship. Imagine two lines drawn from the center of the submarine: the first through the bow dead ahead, and the second to the target. The angle between these two lines, measured clockwise from the first line, is the relative bearing. A target dead ahead is at 000 degrees relative. Since there are 360 degrees in a circle, dead astern is at 180 degrees relative. These three diagrams show relative bearings of 50 degrees, 160 degrees, and 240 degrees. 7 True Bearings The sonar operator may also be ordered to report a target's true bearing. Imagine two lines drawn from the center of the submarine: the first to the North Pole, the second to the target. The angle between them, measured clockwise from the first line, is the true bearing. A target due North of the submarine is at 000 degrees true, due East at 090 degrees true, due South at 180 degrees true, due West at 270 degrees true no matter where the submarine is heading. Only when own ship is heading due North, will a target's relative bearing and its true bearing be the same. Note how the true bearings are measured in the figures below. 8 Reading a bearing indicator Below is a picture of a bearing indicator. It has three parts: 1. The outer scale represents relative bearings. Zero always points to your own submarine's bow. 2. The inner scale represents true bearings. Zero always points to true north, no matter where your submarine is heading. 3. The diamond-shaped bug has two tips which point out on both scales the direction in which the projector is facing. This is how to read the bearings 1. Read the relative bearing at the outer tip of the bug. 2. Read the true bearing at the inner tip of the bug. NOTE: You can also read your own submarine's course on the true (inner) scale by noting the degrees directly below zero relative. 9 When own ship changes course The diagrams below show that the relative bearing changes when own ship's heading changes. But the true bearing, measured from the motionless North Pole, is fixed. Therefore keeping the true bearing in mind helps the operator maintain contact with a target, no matter where his submarine is heading. Know these general terms The direction of a target may also be described in a more general way, as shown in the diagram at the right. Ahead, astern... port and starboard...bow, beam, and quarter...these are familiar words. But you must learn to know these eight combinations by heart, so that the instant you hear any one of them, you get a picture of the general direction of the target in relation to your submarine. 10

Copyright © 2013, Maritime Park Association
All Rights Reserved
Legal Notices and Privacy Policy
Version 1.10, 22 Oct 04