Short Answer
Safety Note
A compass is a tool, not a guarantee. It must be part of a broader navigation and safety framework. Always cross-check critical data—bearings, positions, weather, tides—with official sources such as national hydrographic offices, coast guard broadcasts, and updated paper or electronic charts. Never use a phone or tablet as your only navigation device; a compass and paper chart should be your backup when electronics fail. Keep paper charts for your sailing area, and know how to plot a position by hand. Take a certified navigation and safety course from a recognized sailing federation or coast guard auxiliary. Follow the International Regulations for Preventing Collisions at Sea (COLREGS) and local maritime rules at all times. A compass can tell you where north is, but only a well-trained, situationally aware sailor can use that information to keep the boat and crew safe.
FAQ
What is magnetic declination and why does it matter?
Magnetic declination is the angle between true north (used on charts) and magnetic north (where a compass needle points). It varies by location and changes slowly over time. If you ignore declination, your compass course will be off by that angle, which can put you miles off course over a day of sailing. Always check the chart's compass rose and apply the correction.
How do I take a bearing from a chart?
Draw a line from your position to your destination. Place the compass edge on the line with the direction-of-travel arrow pointing toward the destination. Rotate the housing until the orienting lines are parallel to the chart's north-south grid lines and the orienting arrow points north. Read the bearing at the index pointer. That is the true bearing; convert it to magnetic by applying declination.
Can I use my phone's compass instead of a real compass?
A phone compass can be useful for a quick check, but it is not reliable enough for primary navigation. Phones are affected by magnetic interference, battery drain, and water damage. A quality baseplate compass or a properly adjusted steering compass should be your primary magnetic navigation tool, with the phone as a backup only.
What is a back bearing and when should I use it?
A back bearing is the reciprocal of a bearing—180° opposite. If you take a bearing to a landmark behind you and it matches the back bearing of your intended course, you are on the line. It is a quick way to check for cross-track error without plotting a full position fix.
How do I correct for compass deviation on my boat?
Compass deviation is caused by metal and electrical fields on your boat. It varies with heading. The standard method is to have a professional compass adjuster 'swing' the compass—rotate the boat through known headings and record the errors—then create a deviation card. You apply the deviation correction in addition to magnetic declination when converting between true and compass courses.
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