Once you lay out a course on your chart, you need to convert that course to the proper compass course to follow. You may need to do some conversions between true, magnetic and compass courses. Fortunately, this is not difficult. The basic conversion formulas are intimidating when written out, but there is a user-friendly way to make calculations that involves making a list, filling in the values and doing some simple math. Here is the list:

True
Variation
Magnetic
Deviation
Compass

There are a variety of mnemonics to help remember this, such as "True Virtue Makes Dull Company." The idea is to fill in values by pulling information from charts and tables, and calculate the rest. When proceeding down the column, add westerly and subtract easterly variation and deviation. Obviously you do the opposite when working up the column. For example:

True – 145
Variation – 10E
Magnetic – 135
Deviation – 5W
Compass – 140

Gene BjerkeTable 1
Gene BjerkeTable 2This means you start with the true heading of 145 degrees and subtract 10 degrees to account for the variation (both pieces of information gleaned from your chart) to arrive at the magnetic course of 135 degrees. You then add 5 degrees to account for deviation (information that is specific to your boat, and comes from your tables) to arrive at a compass heading of 140 degrees. Thus you would steer a compass course of 140 to maintain a magnetic course of 135 or a true course of 145. These are all exactly the same course, just measured in different ways.

STEERING WITH THE COMPASS

When steering by compass, the first thing is to trust your unit. In my early days, I sailed into a bay and looked around. The compass said to go one way, but it looked to me like I should go a different way. So I went the way I thought I should go and ended up on the opposite side of the bay too late in the day to make it to my destination. Not a good scene.

To make sure that you can trust it, keep anything that might attract the magnets several feet away from the compass. That includes tools, knives, flashlights, portable radios – anything that might include iron or magnets. When in doubt, keep it away.

A modern compass is a robust instrument. With a little care it will last for many years. Cover your compass to protect it from the sun when you are not using it. As you are cruising about, check that it reads correctly on your familiar courses. If the card sticks or a bubble develops, take it to a proper compass repair shop.

Next, remember that although the card appears to move, it is really the boat changing directions – the card generally stays steady. This may make it easier to know which way to turn in order to get back on course. But don't correct too much. Beginners tend to try to correct every little deviation from the course. That will lead to endless sawing away at the helm, or what a mate once referred to as "writing your name with the wake." Know that a boat will tend to wander somewhat as it gets pushed around by the waves, but it will wander in both directions. The best helmsmanship consists of doing the minimum amount of steering to make the boat stay on the required course.

So relax, look around and pay attention to other things beside the course. Watch the tides, the winds and the bow against the horizon. Getting a feel of the world around you helps give you a sense of what is happening to the boat. And check the compass at intervals to make sure you are still going where you want to go.