VFI, Heeling error

VFI, Heeling error

VFI
Vertical Force instrument.
Graduated compass needle attached with sliding weight.
Rides on a sharp pivot point.
Housed in a brass case.
Graduated compass needle can align itself with Earth’s magnetic field.
Sliding weight can move in or move out from center.
By measuring the sliding weight distance, vertical force is found.

Heeling error Cause:
Ship’s permanent component (R).
Induced by Z into VSI, acting through the compass position.
Induced by Z into athwartship HSI, when vessel heels.
Compensation:
Vertical force instrument (VFI) when vessel upright.

First cause of HE:
Ship’s permanent component (R).
By convention,
If vertical force downward: +R. (In NH)
If vertical force upward: -R. (In SH)
Since, most vessels are built in northern hemisphere, so it is said that vessel have: +R.
Remember,
Max HE deviation on N or S heading.
Zero HE deviation on E or W heading.
HE varies as cos compass course.
+R causes HE deviation to high side.
-R causes HE deviation to low side.

Second cause of HE:
Induced by Z into VSI, acting through the compass position.
Remember,
HE varies as cos compass course.
In Northern hemisphere, HE deviation to high side.
In Southern hemisphere, HE deviation to low side.
At equator, no induced.

Third cause of HE:
Induced by Z into athwartship HSI, when vessel heels.
Remember,
HE varies as cos compass course.
In Northern hemisphere, HE deviation to high side.
In Southern hemisphere, HE deviation to low side.