Chapter - 09

The Compass

Trust Your Compass

As An introductory remark we should like to advise everyone to *^- believe in his compass. Many more disasters have occurred on account of one's disbelief in his compass than to the contrary. It is true that the compass has errors but these errors are easily determined and after they have been determined make the compass as accurate as a watch. Therefore, believe what your compass tells you and it will always guide you to safety provided you are careful not to let any magnetic substance cause any unknown error.

The Magnetic Poles

When reference is made in this text to a magnetic north pole, it must be understood that this is not a precise point toward which the compass needle points exactly. It does point to it, approximately, because the needle tends to align itself with lines of force surrounding the earth, terminating at the North and South Magnetic Poles, the locations of which do not coincide with the geographic (true) poles. Since these lines of force are not straight, the compass may point slightly east or west of the magnetic north pole at any given point. The magnetic north pole is located in an area somewhat north of Hudson Bay; the geographic (true) north pole is at the extremity of the earth's axis of rotation.

What The Compass Is

The compass is nothing more than a magnet suspended so as to be allowed to swing freely in a horizontal plane. In theory, an ordinary knitting needle magnetized by drawing a toy magnet along its length a few times, and suspended from the center by means of a thread so that it can swing in a horizontal plane, is as much of a compass as the ones we use on our boats to-day. If such a needle is magnetized and suspended it will immediately assume a north and south position.

But the compass, as we know it, consists of a number of magnetized needles bound together, and suspended or pivoted from beneath. On this bundle of magnetized needles we have a card mounted to give us a better sense of direction, and allow us to determine directions other than north and south, which would be the only two indicated by the magnetized needles if we had no card mounted thereon.

There has been little or no change in the mariner's compass for centuries. In theory and construction, it is practically the same as it was more than one hundred years ago. The only changes which have been made are refinement in its construction, and the markings on the compass card.

The Dry Compass

The older compasses were known as dry compasses; that is, simply magnetic needles and a card pivoted at the center. Naturally such an arrangement was very sensitive and responded to the motion of the ship very freely. With the coming of the steam engine, and later, the internal combustion motor, it was found that the vibrations set up by the machinery were such as to keep the compass card in constant motion, which naturally made it unreliable as a navigating instrument. The development of the liquid compass followed, and this type overcomes to a large extent the difficulty and trouble experienced with the dry compass.

The Liquid Compass

The liquid, or wet compass, is practically no different from the dry compass, with the exception that a liquid generally consisting of a mixture of 55 per cent, water, and 45 per cent, alcohol is introduced into the bowl of the compass, and then the latter is sealed up. The liquid not only prevents the compass needle and card from responding to small vibrations due to power plants and the sea, but also tends to buoy up or float the needle and card, and thus make it rest more lightly on its pivot. This allows the card to turn more freely as the ship is turned, or rather to hold its position more steadily as the ship's bow is turned away from the compass.

The smaller and less expensive compasses use kerosene as the filling liquid, and some of the newer makes use oil instead of alcohol and water. On account of the nature of the various kinds of fluids used, the compass as we know it is practically non-freezable in ordinary latitudes.
 
One of the great advances in the construction of modern compasses is the development of the spherical compass. This has a hemispherical shaped glass top which magnifies the card. Furthermore, with this type of construction, the card is much steadier.

The Lubberline

Compasses are fitted with a gimbal ring to keep the bowl and card level under every circumstance of a ship's motion in a seaway, the ring being connected with a binnacle or compass box by means of journals or knife edges.

On the inside of every compass bowl is drawn a vertical black line called the lubberline, and it is imperative that the compass be placed in the binnacle or on the boat so that a line joining the pivot and the lubberline shall be parallel to the keel of the boat. Thus, the lubberline always indicates the compass direction on which the boat is heading.

The Cord

While a compass card may be graduated in either points or degrees only, most of those used today on pleasure craft show both systems. The outer edge of the card has its circumference divided into 360 degrees, usually with each tenth degree numbered. This reads from 0 degrees at North clockwise around to 360 (0).

Just inside this there is a concentric circle graduated in 32 major divisions known as points, each subdivided ordinarily into half-points and quarter-points.

An older type of card had degree markings running from 0 at North and 0 at South to 90 degrees at East and West.

The card divided into 360 degrees is known as the Navy type, while the one divided into both degrees and points is used by the Merchant Marine. On the Navy card, the only points indicated are the four cardinal and four inter-cardinal points, shown by heavy markers.

Points

Division of the compass card according to points is a most interesting one. While the use of the card divided into degrees from 0 to 360 is becoming more popular, many boatmen prefer the point system. It is well to be familiar with both.

As mentioned above, the card is divided into 32 major divisions known as points, each one of these points having a particular name. The four principal or cardinal points are known as North, South, East and West.
 
The inter-cardinal points are the ones midway between the cardinals, and these are given a name which is a combination of the points which they bisect; that is, the point midway between North and East is known as Northeast, etc. This gives us eight divisions.

We now subdivide these eight divisions in half, and once again we give these eight new points names which are combinations of the two points which they are midway between. For example, the point midway between North and Northeast is North Northeast. That point midway between South and Southwest is South Southwest.

The illustration above shows four types of cards available today. Card A has its outer edge divided into 360 degrees, quarter-points concentrically arranged on the inner circle. Card B is Navy style, divided into 360 degrees, clockwise from 0 at North to 360, every 10th degree numbered. Cardinals and intercardinals are the only point divisions indicated on this type of card. At C, the quarter-points show at the outer edge while the 360-degree divisions are superimposed upon the quarter-points. At D, the card is divided into quarter-points only. Many prefer cards C and D for sailing vessels because of their plainness

To get the additional 16 points it is simply necessary to divide points which we have already determined in a similar way as before. Here again the new points will have names corresponding to the points to which they are adjacent. The word "by" will be used in all of these 16 new points. For instance, the point between North and North Northeast is known as North by East, because it is adjacent to North, and in an easterly direction from North. The point between Southeast and South Southeast is known as Southeast by South, because it is adjacent to the inter-cardinal point Southeast, and in a southerly direction from it.

Quarter Points

For the purpose of steering more accurate courses than would be possible by following only 32 points, we must subdivide the points into halves and quarters. The naming of these quarter points is most interesting, and must be thoroughly mastered by the motor boatman.

Naturally it will be seen that every quarter point might have two names; that is, it might refer to the point either to the right or to the left of it. For example, the quarter point just to the right of North could logically be called North 4. East, or it might be called North by East ¾ North. Either of these designations would probably convey to the man at the wheel the course which it was desired that he should follow. However, and perhaps unfortunately, there is a certain method of calling these quarter points, and again we are confronted with two methods instead of one.

The older method appears to many to be the most logical one, although both are correct.
Pages 118 and 119 give a complete comparison of the point and degree methods of naming compass directions. It is not assumed that this table will be memorized but its existence should be kept in mind for future reference.

Mounting The Compass In The Boat

A compass may be of the most expensive type and, in itself, highly accurate yet useless in running courses if it is incorrectly installed in the boat. The lubberline, as has been pointed out, represents the boat's head but only if the compass itself is so placed with respect to the keel or boat's center line that it too will lie in a line parallel with the keel.

When possible, it is well to have the compass in the boat's center line, over the keel. It should be located ahead of the wheel at a height where it will be easy to read and in such a manner that the helmsman's eye can drop down to it easily without actually having his attention diverted from the course ahead.

If the center of the compass cannot be placed amidships directly over the fore and aft keel line, then a line should be struck parallel to the keel line and the lubberline should lie in this line.

Preferably the wheel and compass, if they must be on one side, should be on the starboard side, giving a clear view of the danger zone from dead ahead to two points abaft the starboard beam.

Electrical wires near a compass may affect it. When two wires are contained in a single cable, the effect of each is neutralized. In the case of single conductor wires, it is well to twist pairs together for the same reason.

The above illustration is intended to indicate one of the two ways of naming the quarter points of the compass. The arrows indicate the numerical order of naming the quarter points, viz.: ¼, ½ and ¾, or ¾, ½ and ¼, depending upon the direction of the arrow. In this method of naming the quarter points (which is known as the older method) we work from each cardinal and inter-cardinal point toward the 22½-degree points as indicated by the arrows, thus, N ¼ E, N 2 E, N ¾ E, N x E, N x E ¼ E, N x E ½ E, N x E ¾ E, NNE. Now note how the fractional points change, thus: NE x N ¾ N, NE x N ½ N, NE × N ¼ N, NE x N, etc.
 
The illustration on the right indicates the other or newer or Navy method of designating quarter points. As before the arrows indicate the numerical sequence of the fractional points thus: N ¼ E, N ½ E, N ¾ E, N x E, N x E ¼ E, N x E ½ E, N × E ¾ E, N NE, N NE ¼ E, N NE ½ E, N NE ¾ E, NE x N. Now a change to this: NE ¾ N, NE ½ N, NE ¼ N, NE, NE ¼ E, NE ½ E, NE ¾ E, NE x E, NE × E ¼ E, NE x E ½ E, NE × E ¾ E, E NE, E NE ¼ E, E NE ½ E, E NE ¾ E, E x N, E¾ N, E ½ N, E ¼ N.

The table on pages 118 and 119 also shows the two methods.

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