A Simplified Guide to Small Marine Craft Navigation.

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Chapter 7 (v.1) - Reading the Compass Card.

Submitted: December 05, 2016

Reads: 141

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Submitted: December 05, 2016

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Reading the Compass Card.

 

There are three different notations used in reading compasses. In practice, you will rarely find a compass card showing all three of these notations. Some show only two notations, but most only one.

The three notations are as follows.

 POINTS NOTATION, in which each quadrant of the card is divided into eight equal parts, the division mark being called a point, each with a distinctive name such as North-by-East ,written as N x E, North-North-East, written as NNE, North-East by North, written as NE x N, and so on. Each point is thus 11%° apart and the term point is still used with this significance. Although the points notation for the compass reading is now largely obsolete, the system is frequently used for indicating general or approximate directions, such as the wind direction in weather forecasts. Sailing Ships used to steer to the nearest point or half-point, but with the advent of power-driven vessels steering became more accurate and the compass card became graduated in degrees.

QUADRANTAL NOTATION, this was the first system of degree marking adopted. Each quadrant of the card being graduated into 90° with zero at North and South, and 90° at East and West. In this notation, the cardinal directions were simply named North, South, East and West, while intermediate directions were named in degrees from North or South towards East or West. The direction of South-East, for example, was described as South-forty-five East and written as, S45°E‘ the direction West-North-West was described as North—sixty-seven-and-a-half West and written as, N67%”W.Four.

THREE-FIGURE NOTATION, The system from 000° to 359° is what most modern compass cards are graduated in since there is no longer any reason for retaining the somewhat confusing old style. Whereas it is true that it is impossible to steer a small craft to exactly a degree, most experienced navigators agree that the points or quadrant notations and the confusing conversion involved to and from the three-figure notation necessary for chart work is likely to lead to unnecessary errors.  Therefore, for navigation it is recommended the three-figure notation system be used for all navigational purposes, bearings, courses and steering, since as previously stated the older system can be very confusing.

In addition, any navigator should be aware of the other systems and be able to convert from one system to another should the need arise. Therefore, all navigators should make themselves thoroughly familiar with the compass card in all its forms.

Small Marine Craft steering compass cards usually show the three-figure notation in abbreviated form. This is because the cards are small and the compass must be clearly legible at some distance and sometimes in a poor light, so the degree markings and figures must be well separated and hold. The ’number of markings and figures will depend on the size of the compass card.

The smallest cards would be marked as shown on the right-hand card in the illustration below, at every 5°, each 10° mark being bolder, and figures every 20°. Larger cards may be marked as shown in the left-hand card in the illustration at every 2° and 5°, with bolder marks and figures every 10°. The last digit, and the first up to 100° is omitted to permit a larger figure being shown. For example, against the 020°a number 2 and against the 280°a number 28 is shown, and so on.

 

 

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The Points and Quarter Points Notation System

 

 

 

  

The Quadrantal Notation System

 

 

 

 

 

 

 

 

 

 

 


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