Compass Fundamentals: Nautical Compass

Compass Fundamentals: Nautical Compass

Abigail ScottByAbigail Scott
Updated on 8/13/2022

If you are sitting in the cockpit, looking at the nautical compass will tell you which way the boat is pointing, but it won't necessarily mean where it is going. Your bow may be pointed ENE slightly even if you're drifting in the northeast. All of this is considered to be a component of "navigating," but for the time being, let's focus on the compass that is located on your deck.
A land compass is often round and flat like a pocket watch, and it may also be mounted to a flat base. On the other hand, a "marine" compass refers to the dome-shaped bulb compass that is used by many boaters and has a dial that revolves on a pivot. Typically, it will have an N/S needle that is free to rotate. The majority of kayakers will either permanently or temporarily fasten these components to the bow deck of their craft by employing a bungee cord, strap, or some other type of tie-down system.

nautical compass

In a marine compass, the N-S line of the compass should be orientated so that it passes through the pivot point on the compass display and an index mark on the base of the compass. This type of line is known as a "lubber's line." This line should be linked with the centerline of the vessel, with the bow pointing north and the stern pointing south. Taking the time to properly align the N-S line is essential because even a minor deviation of a few degrees might cause your readings to be inaccurate.

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The Compass Rose And Its Variation On The Compass

The compass rose, which is found printed on the majority of nautical maps, is used in combination with the maritime compass. The rose contains essential information that can be readily applied to the navigational system represented by the compass.

On a compass rose, the circumference of the outer ring denotes "true north" or "geographic north" (see the last article for details on how a compass works). The true North is located at 0 degrees on this outer ring of the compass. The direction corresponding to the geographical North is printed at the top of the map. As a result of the fact that there is a difference between the real North and the direction in which the compass needle actually points – which is referred to as the Magnetic North – the compass needle or dial does not actually point to the geographic North Pole (except in very few places on the globe).

On a nautical compass rose, the following ring inward is the second ring of 360 degrees; however, it is rotated slightly to show the amount of magnetic variation in that particular region that is covered by the chart. The amount of variation is depicted as a rose with its center cut out to reveal it. If you look at it alongside the outer ring, you'll notice that the "North" indicator on the second ring has been shifted to the east or the west by the same number of degrees that are shown on the rose. If, for example, the variation for the area, as shown on the rose, is 12 degrees East, then the North point on the second/inner ring (magnetic North) will be 12 degrees further to the right (east) than the actual True North point. This is because the magnetic North is based on the Earth's magnetic field rather than the Earth's magnetic north pole.

nautical compass

The charm lies in the straightforwardness of utilizing a compass in conjunction with nautical charts. Magnetic bearings are typically used to assist in the reading of charts. You can read directly from the map onto the compass – and back again – without having to make any modifications or perform any math, thanks to the inner ring, which gives you the ability to identify all of the magnetic bearings of landmarks and other similar features.

Sweet, eh? You do not need to make any compass adjustments for variation or true North if you decide from the map that a point of land is 75 degrees (based on the inner ring) from where you are. You may then use that bearing to navigate to the end of the land.

However, things are not always as straightforward as that; factors such as wind, current, and individual paddling styles all contribute to the indirect nature of that approach. If you paddle for thirty minutes and then take another reading, you might discover that the temperature at the destination has risen to seventy-eight degrees. That indicates that you have strayed a little bit to the east of your course. You will need to make some adjustments in order to fit within this new heading. If you maintain your initial heading of 75 degrees but have been drifting, you will arrive at your destination further along the shore than you had planned.

Deviation Of The Compass

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Accuracy

When utilizing a compass, there is one more thing to remember. How can you be sure that the compass is pointing to magnetic north and not, say, the hatchet that you have stashed below deck? You may have to cope with something called "compass deviation." It is simple to establish the joint or opposing bearing using a compass because the dial encompasses the full 360 degrees. The reciprocal of the north is south, which is 180 degrees, or one-half of the whole circle of 360 degrees. The angle that is the common of 110 degrees, which is approximately ESE, is 290 degrees, which is approximately WNW. Position the compass such that it is perpendicular to a clearly defined line that runs between two specific things in order to test for any deviation. First, turn around and take a bearing in the opposite direction immediately behind you ("back"/"away" bearing), and then take an approach on a conspicuous landmark on the line in front of you ("toward" bearing). The second bearing should be the reciprocal of the first bearing, which is equivalent to 180 degrees. Check to determine if the load needs to be adjusted in order to correct it if it is off by several degrees. If this is not the case, you may need to alter how you are reading.

deviation

Suppose you are going in the direction of a bearing that is 280 degrees; the standard approach, sometimes known as the "behind" bearing, should be 180 degrees less, or 100 degrees. Instead, it reads 88 degrees. You are off-kilter by twelve degrees, according to the compass. You will need to alter your reading and select a bearing that is more representative of the norm in order to account for this variation. This indicates that your "toward" bearing is off by 6 degrees, whilst your "back" bearing is off by 6 degrees. You must consequently adjust your away approach by adding half of the compass deviation of 12 degrees and adjust your "toward" bearing by subtracting that same amount. Regrettably, this departure is subject to change. If you are worried that your compass is not accurate, you need to do it frequently.

Considerations To Make When Determining Your Course Bearing

Marking a course line on a piece of tracing paper and then transferring that line to the compass rose is an easy and accurate approach to determining what bearing you need to take in order to reach a specified destination. This may be accomplished by following these steps:

1. Choose the path that you would like to follow. Could you make a note of it on your graph?

2. Trace the True N-S line and the course line onto the sheet using a sheet of acetate or tracing paper, whichever you have available.
3. Place the overlay that contains your course as well as the True North-South line on top of the Compass Rose that is written on the chart.
4. Verify that your True North-South line is aligned with the lines on the chart, and then adjust your overlay such that the course line passes through the middle of the Rose. Maintaining its centered position, move the course line until the end of it touches Rose's inner ring (Rose's inner circle serves as the magnetic bearing ring).

5. The compass bearing that is given on the inner ring is the bearing that you should follow in order to arrive at your destination.

The Art Of Hedging Your Bets

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When making a long crossing, some kayakers find it more convenient to steer purposefully slightly wide, either to the right or the left of their mark, in situations where visibility is poor or when the effects of a current are being felt. They are aware that after they reach their objective region, they must then travel either left or right in order to hit the mark exactly. If everything else remains the same, a relatively minor adjustment to the intended bearing can provide you with a "side" advantage.

You calculate that if you take a bearing of 45 degrees, you will arrive at the easternmost point of the headland that you are looking for. Although the amount of drift that will occur will be modest, you still want to add some insurance to your path, so you purposefully steer to a cove that is slightly farther to the left (west) than 45 degrees. When you reach the opposite beach, even if there is fog or some other kind of reduced sight, you may be relatively confident that your objective is a short distance to the right (east).

If you take a glance at the nautical compass, you will be able to determine in which direction the boat is pointed, but this does not necessarily guarantee where it will end up.