The deviation chart

If we are allowed to sail in zones 1 and 2 we necessarily take on board a deviation chart where values ​​are indicated deviation from our steering compass which we update every five years.

The process to draw a deviation curve is easy but requires following a rigorous methodology. Stated simply, it is to subtract the indication of direction given by a secondary compass, situated in a boat free magnetic influences, the indication of the direction given by the compass of government.

Importantly, the concept of deviation is purely magnetic, so we have to compare directions relative to magnetic north and not make the mistake of comparing the magnetic compass heading of government with the true course that indicate equipment electronic navigation as for example the GPS signal. Today may seem a bit illogical that, having electronic equipment on board that indicate real directions, we have to develop a tablet magnetic detours, but the rules is mandatory. Anyway I am particularly of the opinion that we should never forget navigate without the help of electronics that, during the voyage, may fail for a thousand reasons.

The deviation chart
Posted on 04/04/2017by Jordi Maseras
If we are allowed to sail in zones 1 and 2 we necessarily take on board a deviation chart where values ​​are indicated deviation from our steering compass which we update every five years.

The process to draw a deviation curve is easy but requires following a rigorous methodology. Stated simply, it is to subtract the indication of direction given by a secondary compass, situated in a boat free magnetic influences, the indication of the direction given by the compass of government.

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If the boat has two or more stages, you only need to have the tablet Main compass. Photo: Jordi Maseras.

Importantly, the concept of deviation is purely magnetic, so we have to compare directions relative to magnetic north and not make the mistake of comparing the magnetic compass heading of government with the true course that indicate equipment electronic navigation as for example the GPS signal. Today may seem a bit illogical that, having electronic equipment on board that indicate real directions, we have to develop a tablet magnetic detours, but the rules is mandatory. Anyway I am particularly of the opinion that we should never forget navigate without the help of electronics that, during the voyage, may fail for a thousand reasons.

Turnout tablet a pleasure boat.
Turnout tablet a pleasure boat.
To start drawing tablet will use a compass deviation of situating Dials standing on the foredeck. To do this, we will choose a day of good visibility and calm sea. Once away from the coast at least 3 miles, will match a dial with compass delay and describe various circles, with the least possible radius and low speed. While performing circles, dialing delay must be constant. In this way we will ensure that the area is free from disturbances. Otherwise, we will choose another area and repeat the operation until we find a place free of disturbances. When we find the right place, we will take 15 courses in 15 degrees starting from a first reading heading north. (0, 15, 30, 45, 60, etc.). In each heading we write down all the differences between the two measures that mark. Registered securities may be negative or positive. When we have finished operation will only move data to the tablet detours and thus obtain the offset curve.

If the resulting curve indicates values ​​between -7 ° and + 7 will suffice to consider the data indicated by the table to perform a calculation direction. If indicated values ​​between +/- 20 ° +/- 7 ° and the compass on board must be compensated by clearing system (small screw on the back). If the curve indicates greater than +/- 20º values ​​need to change the location of the measure to remove him from the ferromagnetic effects acting on it.