A compass is a wonderful tool that revolutionized travel across water. Out at sea in the middle of the ocean, there are no landmarks to guide you. Steering a straight line is remarkably difficult to do, and maintaining a course is practically impossible! A compass works on the simple principle that the Earth has a magnetosphere and the compass is merely a magnet suspended in an oil bath and allowed to orient itself with the magnetic field of the Earth itself. The pretty card that tells you North, South, East, and West is just a cheap card stuck to the magnet to make it look more impressive! The truth relies on the fact that magnetism guides us across the oceans of the world!
While we are talking about magnetism, I find it important to say that we do not have a light in our compass for use at night and this was a conscious decision that we made before we left to go cruising.
Magnetism is a phenomenon that can be created with permanent magnets and also by electromagnets. The mere act of running an electrical current down a wire will produce a, albeit very small, electromagnetic field. Why would you wan’t to put a magnet next to your compass?
Yes, compasses that have lights are shielded to protect them from this influence, making it safe to have a light in your compass so that you can read it while on watch at night.
By day, we can see the compass clearly and we look at it from time to time. The sun illuminates everything and we are sailing along without any issues. This doesn’t mean that we are glued to the compass. When the sun is shining and we can see the compass, we only look at it every few hours to make sure we are still on course.
Being a sailboat, the sails are powering the boat at all times. This means that our direction of travel is not our ideal course but instead the angle to the wind that our sails are set to. We rarely steer the boat by hand as our wind steering does all of this for us. If the wind shifts, the wind steering will alter course to keep the sails to the prescribed wind angle and this means that the sails are always perfectly trimmed, even if the wind shifts.
Wind shifts are why we check the compass. If the wind shifts, we are going to start sailing on a new course and therefore need to adjust our angle to the wind to sail to the desired course. This doesn’t happen every few minutes, instead it happens every few hours, and that is when we look at the compass.
By night, the compass is dark and hard to see (but if there is a full moon, you can see the compass with ease), but this doesn’t matter because the few times on night watch that we need to check the compass, we simply turn on a flashlight and take a look! Once that is over, we turn off the flashlight and let our eyes adjust back so we can continue to enjoy the stars.
Why is the compass of little importance while on night watch? Because the stars are out. On night watch, we simply look up at the sky and locate the North Star. If the boat is maintaining its course, all night long the North Star will stay in the same area of the sky relative to the boat. For example, if the North Star is on the port side just forward of the bimini (when viewed from the helm) then all night it should stay there since the North Star doesn’t move in the night sky. If you look up and notice that it has moved to a different part of the sky (relative to the boat) then you need had a wind shift and need to adjust the sails and windvane accordingly to bring the yacht back on course.
When setting a course, the compass is necessary. I can look into the sky and see where the North Star is but I can’t set a course by it. The compass lets you set a precise course that will get you towards your desired waypoint. Since we are at the mercy of the winds, our acceptable course is +/-20 degrees of our desired course. This means that if our desired course is 80, but the winds only allow us to sail at 74, then 74 is great! If the winds shift a bit and suddenly we find ourselves down to 65, this is still fine and we keep sailing along content with our heading. If we start veering even further and start sailing along at 58, we would consider tacking to bring us somewhere between 80 and 100. We find that we sail with the best VMG (Velocity Made Good) when we are about 70* off the wind. This means that pinching just isn’t worth it for us when we are crossing an ocean. We will sail on an undesirable course for days if it sets us up for a more favorable and more comfortable tack in the future.
All the while, we rarely look at the compass and therefore do not have a light in our compass as the very slight risk that the light might throw off the compass isn’t worthwhile for an instrument that we infrequently use!
