Figure 10-8.--F and Q coils.
F1-Q1 and FP-QP Coils
magnetization, the result of the two magnetic fields
would be equal to zero. This is not possible to attain,
In many installations the conductors of the F and Q
and as a result, the M-coil field is always considerably
coils are connected to form two separate circuits
less than the vertical field. The vertical permanent
designated as the F1-Q1 coil and the FP-QP coil. The
magnetization of a ship is constant while the vertical
F1-Q1 coil consists of a F1 coil connected in series with
induced magnetization varies with magnetic latitude,
the Q1 coil so the current is the same in both coils. The
roll, and pitch, but not with heading. Consequently, the
same is true for the FP-QP coils in that they are also
M-coil field strength must be changed when the ship
connected in series and the same current is in both coils.
changes magnetic latitude to keep the M-coil field as
Installations with both F1-Q1 and FP-QP coils are known
nearly equal and opposite to the field produced by the
as split-coil installations because the F and Q coils are
ship's vertical magnetization.
split into two coils.
The F1-Q1 coil is used to counteract the magnetic
F and Q Coils
field produced by the ship's longitudinal induced
magnetization. The coil field strength depends on two
The F (forecastle) coil encircles the forward
factors--the ship's heading and the magnetic latitude.
As the ship's heading and magnetic latitude change, the
one-fourth to one-third of the ship and is usually just
ship's longitudinal induced magnetization changes
below the forecastle or other uppermost deck. The Q
accordingly.
(quarterdeck) coil encircles the after one-fourth to
one-third of the ship and is usually just below the
The FP-QP coil is used primarily to counteract the
quarterdeck or other uppermost deck, as shown in figure
magnetic field produced by the ship's longitudinal
10-8.
permanent magnetization, and it is sometimes used to
provide some compensation to supplement the M coil
The F and Q coils counteract the magnetic field
produced by the ship's longitudinal permanent and
induced magnetization. The shape of the magnetic field
produced by the ship's longitudinal permanent and
longitudinal induced magnetization and the two fields
are directed below the bow and stem of the ship. Look
at figure 10-9. Here, you can see that the ship's
longitudinal permanent magnetization is constant, but
the longitudinal induced magnetization changes with
heading and magnetic latitude. The F- and Q-coil field
strengths must both be changed whenever the ship
changes course or magnetic latitude. These field
strengths must also be changed if the coil field strengths
would not have the proper values to counteract the
changed longitudinal induced magnetization. Note that
both adjustments must be made, one for the F-coil field
Figure 10-9.--Longitudinal field of ship and neutralizing
strength and one for the Q-coil field strength.
fields of F and Q coils.
10-7
