Why does the deviation differ from the last deviation table?

The magnetic field of a vessel is always changing in small amounts. Some can cause the deviation to change from the present deviation table. This can create problems in navigation when using the magnetic compass, as the enlarged deviation causes the magnetic compass to behave erratically and also cause the compass card to move excessively when the vessel is rolling.

The cause of the increase and changes in deviation can have different origins. There are multitudes of influences which can cause a magnetic compass to become unreliable. Not only the cargo can have influence on the ships deviation also changes in the ships steel, lightning strikes and installation of nearby electronic devices can have an effect.

How/where does the compass adjustment take place?

Depending on the port and port stay of the vessel, the compass adjuster will usually make a pre-inspection to check the magnetic compass, last deviations table, compass logbook and check if all the needed data and correctors  (spare) are available. If during this pre-inspection the compass adjuster finds something wrong our fully certified compass service department can overhaul, repair or replace your damaged compass or binnacle in time for the vessel to leave without any delay. This pre-inspection is dependant on your schedule and availability.

If any correctors are missing or damaged we have the most common types in stock for fast delivery. Also we have spare magnets of all types of magnetic compass manufacturers in stock, so there is no need to cancel the compass adjustment due to the

non-availability of the correct magnets.

If all is found in good working order the compass adjuster will keep in close contact with the vessels Port Agent and will board the vessel prior to departure where he will sail with the vessel out to sea. There the compass adjuster will perform the compass adjustment during a compass swing(s) and remove/ decrease the deviation close to zero. The deviation that is left will be noted on the deviations table and handed over to the master prior debarkation.  Depending on ships size the compass adjustment can also be

completed inside port limits to minimise costs.

How long does the compass adjustment take and what delays are there for the ship?

Usually the actual compass adjustment itself takes 1 hour 30 minutes of swinging the ship. After the compass adjustment the compass adjuster leaves along with the pilot.

What has influence on the validity of the deviation table?

The main reason for compass adjustment and issue of new deviation table is an increase in deviations. However, inspections by Port

State Control, Vetting inspectors and Flag State Audits can also trigger the need for adjustment of the compass.

How can I check that the compass is working properly?

The only way to check that a magnetic compass is working correctly before magnetic compass adjustment is to use a small screwdriver to deviate the magnetic compass heading 2 degrees.

After the screwdriver has been moved away, the magnetic must return back to the starting heading within 5 to 10 seconds.

What causes the deviation change at certain latitudes and in different hemispheres?

One of the most common causes of deviation is caused by an incorrect placed amount of Flinders bar during a previous compass adjustment. This is indicated by increasing and decreasing deviation when a vessel is sailing on Easterly (SE-NE) and/or Westerly (SW-NW) headings in a large difference in latitudes.

A certified compass adjusters can remove these deviations.

Because the compass adjuster needs the data from the compass logbook to decrease these changes in deviation it is of the utmost importance that all data in the compass logbook  is true and accurate to be sure the compass adjustment  is successful.

Also the last deviation table which was

handed to the master during the last compass adjustment should be available.

How long do I wait before readjusting the on-board compass of a new build vessel?

Depending on the length of the vessel, it can take a period of time for the magnetic field in a new build vessel to settle. For vessels 100 meters in length 5 to 6 months and typically  8 to 9 months for vessels greater than 180 meters.

Why does the compass binnacle only have 1 or no globes?

Due to the influence of the ships magnetic field on the magnetic compass it may be the case that on some headings the deviation is over compensated and then there is no need to remove 1 or even both Globes

(D-correctors) during the compass adjustment.

An inspector found that there is a significant difference in the lifeboat(s) compass heading, why?

Lifeboats have their own magnetic field which is usually too small to affect their magnetic compass.

However, because this lifeboat is on-board the ship, the ships magnetic field has large influences on the lifeboat(s) magnetic compass as this compass has not been adjusted for this extra influence.

After all if the lifeboat is used it will no longer have the     influence from ships magnetic field and     magnetic compass will show the

correct heading.