Last year I bought a Plastimo Mini Contest compass in Australia.
At around $200 it was half the price of same unit in Japan.
Bought it back here and fitted. I noticed that there was no compensators inside when I fitted it.
When I was testing my sheet to tiller I noticed that the compass was out by a fair bit (8 to 12 degrees).
So went back to the info sheet and found that it is preset for Zone C (which of course is Australia).

Just checked the Plastimo page:

Deviation correction :
If deviation is no more than 7? : simply draw a deviation table assessing the error, and keep it for future reference.
If deviation is between 7 and 20? : we recommend that you have your compass compensated as a start, and then draw a deviation table. The compensation procedure is a delicate operation and should ideally be carried out by a professional compass adjuster.

There are no compass adjuster within mile of where I am and I remember setting myself with a plastic screwdriver years ago,
So I will draw up a deviation chart.

Two questions.
1. What happens when someone buys a zone C compass and sails into zone A (the twilight zone)? Around the world racers?
The Plastimo advice to draw up a deviation card cannot work in the middle of the ocean where there are no marks to take bearings from.

2. With no obvious compensators, how do I adjust it.

Gary

Did you Know?A compass needle will experience 'dip' (also known as magnetic inclination) due to the spherical shape of the earth. At the equator the lines of magnetic force will be almost parallel to the earth's surface but as you move towards the poles they will be increasingly angled toward the surface giving the compass needle more 'dip'. In theory at the centre of the poles (north or south) the lines of magnetic force should be exactly perpendicular to the earth's surface. In reality what happens to the compass needle is that it becomes unstable, wanting to dip a great deal but unable to do so.Compasses are specific and pre-set for whichever hemisphere they are to be used in. This is because the needle 'dips' in an opposite direction in the northern hemisphere (head down) to that in the southern hemisphere (tail down).
Copied from the mighty internet!

Cant remember the last time I used a deviation card. With gps and plotters etc hardly anybody uses them. I have made them from a gps reading. But havnt had to use them for a long time.

Cisco, because of the magnetic dip referred to above, the needles are either offset from centre or weighted to one end so the needle remains somewhat parallel to the earths surface. The 3 zones would be south, equator and north. A cheap basic compass will be good only for the zone it was manufactured for. The needle will dip and touch the card and not move if you took it into the opposite hemisphere.

Great nemonic though

garymalmgren said..
Last year I bought a Plastimo Mini Contest compass in Australia.
At around $200 it was half the price of same unit in Japan.
Bought it back here and fitted. I noticed that there was no compensators inside when I fitted it.
When I was testing my sheet to tiller I noticed that the compass was out by a fair bit (8 to 12 degrees).
So went back to the info sheet and found that it is preset for Zone C (which of course is Australia).

Just checked the Plastimo page:

Deviation correction :
If deviation is no more than 7? : simply draw a deviation table assessing the error, and keep it for future reference.
If deviation is between 7 and 20? : we recommend that you have your compass compensated as a start, and then draw a deviation table. The compensation procedure is a delicate operation and should ideally be carried out by a professional compass adjuster.

There are no compass adjuster within mile of where I am and I remember setting myself with a plastic screwdriver years ago,
So I will draw up a deviation chart.

Two questions.
1. What happens when someone buys a zone C compass and sails into zone A (the twilight zone)? Around the world racers?
The Plastimo advice to draw up a deviation card cannot work in the middle of the ocean where there are no marks to take bearings from.

2. With no obvious compensators, how do I adjust it.

Gary

If your boat was in survey you would have to pay for a compass check or compass swing as some of us on this forum used to do years ago on aircraft. First you have to find a licensed compass bloke. Then pay his traveling expenses and at least one night in a motel. Take a day off work and spend several hours driving your boat in circles close to known lead lines. The compass adjuster uses a compass set on a tripod and compares to yours, makes a deviation table and adds correction magnets to your compass. They are like half a match stick and just get stuck on with Blu-tack. These invariably fall off but it does not matter as you will just be navigating with a plotter or GPS anyway. For survey purposes it's all about the certificate. I have a Plastimo Contest and it's immaculate. I will go months with out ever pulling off the cover!
It's variation that changes as you sail from zone to zone. Deviation is the effect of stuff messing with your magnetic compass. Steel or electrical currents etc. I would suggest making a deviation table just as a matter of interest but not bother with trying to steer a magnetic course. Stick with using True and steer with a GPS read out. I just use the heading marker on my plotter.

Trek said..
We use GPS all the time as Ramona does. But magnetic compass doesn't need a satellite network, doesn't need complex electronics to work flawlessly, doesn't need you to be moving to point to North, and will work 100 years without batteries

The fluid will leak out and the plastic gets murky. Keep the cover on the compass and you might get a few years out of them.

Ramona said..

Trek said..
We use GPS all the time as Ramona does. But magnetic compass doesn't need a satellite network, doesn't need complex electronics to work flawlessly, doesn't need you to be moving to point to North, and will work 100 years without batteries

The fluid will leak out and the plastic gets murky. Keep the cover on the compass and you might get a few years out of them.

My Suunto compass is nearly 12 years old. It was a big investment at the time, so it's been looked after - living in the cabin and only mounted when sailing. It's still full and crystal clear. I guess it all depends on how you look after them.