Reading a Boat Compass
In this age of electronic wizardry when most boats have GPS receivers that can tell your exact location and which direction points to home, a magnetic compass may seem like old technology. But not all vessels are outfitted with marine electronics and you can’t always rely on mobile navigation devices. What if the battery dies just when you’re trying to find your way through unknown waters? Or if the GPS signal is too weak? Don’t worry! The simple magnetic compass can steer you in the proper direction and help you reach your destination.
At L&M Marine, we want you to have a memorable boating experience that doesn’t involve getting lost. We’ve compiled this short guide on reading a boat compass so you can navigate safely and if you have any questions, need help with equipment on your rig, or are looking for a new or used boat, stop on by! Our dealership is in Stapleton, near Theodore and Mobile, Alabama and we proudly serve the areas of Biloxi, Mississippi and Pensacola, Florida.
The Compass Rose and Compass Variation
One of the most fascinating things about reading a compass is that it’s used in conjunction with the compass rose, also known as the wind rose or rose of the winds. In case you're not familiar with the compass rose - it’s the diagram printed on most nautical charts depicting the directions, latitudes, and longitudes. The rings and intermediate directions – North-East, South-East, South-West, and North-West – cut through the primary directions and give it a flower-like shape similar to a rose.
The compass rose includes a set of two rings, the outside ring represents the geographic directions while the smaller inside ring denotes the magnetic directions. As there is some difference between the actual direction and the location towards which the compass needle actually points, the inner ring is turned slightly to account for the variation. With these rings, you can easily make out the magnetic bearings of landmarks. And here’s the best part, you can read directly from chart to compass and vice-versa without any calculations.
Compass Deviation
Besides variation, you must also consider the deviation caused by the effect of magnetic fields generated on board the boat. How do you know the compass is pointing in the actual direction and not at some metallic objects such as the vessel’s outboard or your fishing gear packed below the deck? You’ll have to check the deviation card that comes with professionally calibrated compasses, showing the difference in degrees between the compass reading and the actual course. But if you do the adjustments yourself, you’ll have make up your own card. On most fiberglass rigs, the deviation usually ranges from +2 degrees to -2 degrees for steering compasses and if you’re using a handheld compass, in most cases they don’t require any correction.
Tips for Determining Course Bearing
The best way to pilot your boat in the right direction is to mark the desired route on a piece of tracing paper or a sheet of acetate and place it over the compass rose. Just make sure that you’ve aligned the North-South line with the chart. The next step is to move the tracing paper so that the course line passes through the center of the rose. While keeping it in the center, move the course line until its tip intersects the inner ring. The bearing you get on the inner ring is the compass bearing you need to follow. Once you’ve determined your bearing, you have a pretty good idea of how to reach your destination.
A compass is must-have navigational tool and you should know how to use it before embarking on your next adventure. Remember you can always stop by L&M Marine for more information on how to navigate your boat safely. If you want to buy a new or used boat, we offer a variety of vessels of different makes and models. We’re sure you’ll find the right fit for your budget and lifestyle. We also have a state-of-the-art service and parts department. Our marine experts will help you to keep your boat running like new. We proudly serve the areas of Stapleton, Theodore, and Mobile, Alabama as well as Biloxi, Mississippi and Pensacola, Florida.