Nautical needle

Installation and disturbances of the nautical needle

It is the instrument that indicates the direction in which the boat is sailing, therefore thanks to him at all times we can know which direction we are going. They are based on the magnetic properties that magnets have to orient themselves pointing towards magnetic North.

It is basically made up of magnets placed at the bottom of a disc.
called pink where the 360º of the horizon are recorded. This set of magnets and rose has in its center a conical-shaped slit called spire at whose vertex there is a vertical hard stone that is the style, this being the sharp and hard part where the set of rose and magnets rests, and whose function is the avoid friction and allow horizontal rotation of the rose, so it is usually made of a hard material.

All this is put inside a casing called mortar. Closed at the top by a glass, if the spire rotates about a medium in the mortar, which is air, we will call it dry needle, while if this medium is an aqueous mixture of distilled water and alcohol we will call it liquid needle. It has painted some lines of faith that coincide with the bow and stern lines.

We achieve the stability of the needle with a system of Cardan suspension which deals
of always keep the needle parallel to the horizontal planeIn this way, we see that the needle is not a fixed element to the vessel, but rather the needle tilts on the vessel to always remain parallel to the horizontal plane in addition to damping vibrations.

To function correctly, nautical needles must meet two essential qualities: Sensitivity and Stability. The first of them is the property that the needle has, to accuse the smallest fallen angle by the boat on its course. While the second is defined as the property that the needle has, of not be affected by the mechanical effects of the ship, that is, since the boat is always in motion, whether pitching or rolling, the needle necessarily It must be an independent element of the ship, that is, it does not have to be affected by these rolling and pitching. One way to increase the sensitivity of the needle is using multiple magnets, and thus we manage to increase the magnetism captured.

The facility must be in the longitudinal axis within the plane of the center line and with the faith lines in the bow-stern direction to facilitate reading. As far as possible, it will be kept away from electronic navigation devices.

The magnets take the direction of the Earth's magnetic field, so if they suffer any alteration they will will create disturbances in the vicinity of the magnetic needle.

These may be due to:

• Installation of electronic devices nearby.
• Defective electrical installations.
• Air bubbles in the mortar.
• Placing mobile phones nearby.
• Placing metal tools nearby.
• Electric storms.
• Nearby lamps with too much intensity.

Needle Deflection: Definition

The magnetic needle should always point to magnetic North, however it suffers from a phase shift due to the presence of iron masses and electrical and electronic circuits of the boat itself which create a magnetic field that adds to the effect of the Earth's magnetic field, producing what is called the needle deflection, which is defined as: the angle (Δ) What shape of the magnetic meridian with the direction marked by the needle. Therefore:

• Rm = Ra + Δ
• Ra = Rm – Δ

Like the dm:

If the detour is towards W will be negative If the detour is towards E will be positive.

Diversion board

He detour varies depending on the heading to which you navigate, so to obtain it you have to consult the diversion board, or knowing the total Correction, which we will analyze in the next section and the magnetic declination. 

• Ra
• DETOUR Ra
• DETOUR Ra
• -2.0o 285o -2.5o 300o -3.0o 315o -3.5o 330o
• DETOUR
• -3.5o -3.0o -2.5o -2.0o
• 165o 0.0o 225o 180o -0.5o 240o 195o -1.0o 255o 210o -1.5o 270o

Before lifting a board, a compensator will have tried to compensate the needle by placing magnets next to the log, leaving in the end the residual deviations, which are those reflected in the board. The table indicates the deviations to each heading, in increments of 10o or more degrees. The smaller the increment, the more accurate the table will be.