Why, in this world of GPS and other networked marvels, is that so important? Isn’t it enough to know where the boat’s going, and isn’t that the same thing?
Well, no. Where the boat’s pointed and where it’s going aren’t always the same. In fact, they rarely are. A current will cause a boat to move over the ground in a direction different from that in which the boat is pointed.
If we’d had our compass, we’d have known, from the bearing information provided by the GPS, where exactly to look for the mark, and we wouldn’t now be facing a charge of damaging government property.
No matter what vehicle we’re steering, a fixed reference of some kind is an essential aid to pointing it in the desired direction.
Your marine hardware specialists know that while the compass can’t tell us where we’re going, it can tell us what direction we’re steering, which makes it unique. And far from being made redundant by electronic devices, the compass adds to their value. For example, by comparing COG from our GPS to the course steered by the compass, we can detect the presence of a crosscurrent.
Go to http://www.raritaneng.com and see how you can find more information as well as get assistance on marine hardware and on improving your compass using skills at Raritan Engineering.
Adjusting the Compass
A magnetic compass, as long as it’s in good physical order, will always point in accordance to the magnetic field surrounding it. If that field was the Earth’s alone, it would be utterly reliable, but the compass isn’t monogamous, and it’s easily led astray. Onboard magnetic influences-such as those created in some electrical devices and by iron-cause a compass to point askew from magnetic north, an error called deviation.
A professional compass adjustor will “swing” the compass by checking it against known references, such as a proven range or ranges on structures or geographic features. Once on the range, he’ll have the boat slowly motor along the cardinal directions-north, south, east, and west-as indicated by the boat’s compass while he reads the bearing on the range with a pelorus.
Posted at the navigation station, the deviation card allows the navigator to convert a course laid on a chart to a course to steer. Conversely, it allows him to correct a bearing taken by the ship’s compass on a landmark to a magnetic bearing.
Once the ship’s principal compass has been swung and adjusted, have the adjustor also swing and make up a deviation card for any other compass that might be used for navigation, including the one that supplies heading data to the autopilot.
Prior to the widespread use of GPS, you took compass bearings off recognized features in the landscape and plotted them on a chart to figure out where you were.
Because your GPS knows where it is, it can also calculate where it is in relation to any other location in terms of range (distance off) and bearing.
Create a waypoint in your GPS with the coordinates of an accurately charted and identifiable feature, say a lighthouse. Set the waypoint as your destination and steer toward it. The farther you are from the waypoint the better, but a couple of miles provides sufficient accuracy.
Some sailboats and a good many powerboats have two helm stations, each with a compass. Only one of these can be the master compass, so you have to designate one. On a sailboat, this would probably be the one you use when motoring.
Another issue is parallax. This arises when a boat’s steering station is off-center or, on a sailboat, when you steer from the side of the cockpit. If you’re standing behind the starboard helm station and looking over the bow, you’re not sighting down the boat’s centerline. If you aim the bow toward a mark, the boat won’t be heading toward that mark.
So don’t forget these helpful points on how to improve the use of your compass. 1) Keep in mind the movement of the current; 2) create a waypoint in your GPS; and 3) keep in mind parallax.
Click here and see how Raritan Engineering has more information on marine hardware and on how to improve your compass skills.