Seiwa SW AP01 - Manual (Page 34)

Figure 3.5. Socket connections for S81.02 fluxgate.
Steel Vessels
Steel hulls distort the natural pattern of the earth's magnetic field. In many cases these
deviations can be adjusted out through the calibration procedures. In others, a strong
vertical field component may exist which will prevent the compass giving good
performance. It is recommended that the compass be mounted temporarily so that the
best site can be found by experimenting. The following notes should help find the best
mounting:
1. In the first instance, try siting the compass unit below decks but centrally
within the vessel. Keep well clear of vertical steel bulkheads and position
the compass at least 45 cm (18 in) above a steel floor.
2. As an initial check, complete the other steps in the installation and turn the
autopilot onto STANDBY. (The rate gyro option must be turned off for this
test.) Turn the vessel through a full circle, noting at 45 deg. intervals the
difference between the heading displayed and a reference (eg ship's)
compass.
Should the deviations exceed 30 deg. in any position, keep re-siting the compass until
a position giving less than 30 deg. error is found. If errors still exceed 30 deg., the
compass should be mounted above deck level, preferably in the dog house near a
window. If this is done, repeat (2) above.