## Coefficient change due to change in latitude

Coefficient:

Maximum coefficient is caused by one or more ship’s force.

Maximum coefficient is caused by permanent Magnetism+induced magnetism.

Coefficient is measured in degrees.

Coefficient is not a force but produced from force.

Coefficient B, C – change with change in latitude.

Coefficient A, D, E – don’t change with change in latitude.

**Explanation:**

Coefficient B:

B = Bp + Bi

Cause:

Ship’s permanent component (P).

Induced by Z into VSI, F&A.

Effect of parmanent magnetism:

PQR force – Constant deviating force.

PQR – Will not change with change of latitude.

For a constant PQR deviating force,

If magnetic latitude increase – DF(H) get smaller (deviating force get bigger)

If magnetic latitude decrease – DF(H) get bigger (deviating force get smaller)

So, Dev varies as 1/H.

At equator, with strong DF(H), it is harder to deviate compass needle.

Vertical soft iron (VSI):

Ships VSI induced by only Z.

We know, If Magnetic latitude change – both Z change and DF(H) change.

If magnetic latitude increase – DF(H) get smaller (deviating force get bigger)

Also, if magnetic latitude increase – Z get bigger (deviating force get bigger)

So, dev varies as tan dip (Z/H)

If magnetic latitude decrease – opposite.

Coefficient C:

C = Cp + Ci

Cause:

Ships permanent component (Q).

Induced by Z into VSI, athwartship.

Effect of parmanent magnetism:

PQR force – Constant deviating force.

PQR – Will not change with change of latitude.

For a constant PQR deviating force,

If magnetic latitude increase – DF(H) get smaller (deviating force get bigger)

If magnetic latitude decrease – DF(H) get bigger (deviating force get smaller)

So, Dev varies as 1/H.

At equator, with strong DF(H), it is harder to deviate compass needle.

In Practical, Ci doesn’t exit.

Coefficient A, D, E – don’t change with change in latitude.

Coefficient A:

Cause:

Induced by H Unsymmetrical, if vessel swing too quickly.

Coefficient D:

Cause:

Induced by H into HSI, F&A.

Induced by H into HSI, athwartship.

Coefficient E:

Cause:

Induced by H Unsymmetrical distribution of HSI.

Therefore, Ships HSI (F&A, athwartship) induced by only H.

Horizontal soft iron (HSI):

Ships HSI (F&A, athwartship) induced by only H.

We know, If magnetic latitude change – DF(H) change.

But, deviating force due to DF(H) also change.

Therefore, we can tell, if DF(H) get bigger deviating force get bigger.

If DF(H) get smaller deviating force get smaller.

Again, we also know, If magnetic latitude increase – DF(H) get smaller (deviating force get bigger)

So, resulting deviation from HSI remain same in all latitude.