What fluid is in a Compass?

Hi,

There seems to be many mediums.

http://www.newton.dep.anl.gov/askasci/gen01/gen01791.htm

A Compass Adjuster should be able to answer the questions you have about your particular compass.

If you live near the sea and a busy port it shouldn't be to hard to find one of these guys.

My understanding is that compases are filled with "compass oil". I know it sounds strange, but my Dad ruined a compass years ago by adding alcohol to refill it. The alcohol attacked the plastic sight dome and rendered it unuseable. I'd stick with compass oil if it was me.

http://www.vikingoptics.com/compassoil.html

I am showing my ignorance and would appreciate some wisdom from the old hands. I use a smallish fizz boat for fishing fun - not too many miles away from land typically! It is a US built boat and came with some gear. I added a GPS/Plotter together with sounders etc and rarely even look at the magnetic compass to be honest. Given that the compass is a US-fitted model it may perhaps have been balanced for that particular compass zone and obviously not the South Pacific. I know that small handheld dry compasses are balanced according to the various zones they will operate in to stop the needle dipping significantly and catching but are fluid filled compasses similarly vulnerable?? In simple terms, if I had to rely on this compass is it OK here 'downunder' where the Southern bias of the magnetic field is higher?

Hi,

Have you got a deviation card that came with the boat originally?

Have you got a fluxgate compass or heading info on your GPS Display?

If you are fishing the Kaipara it is pretty had to get lost at sea unless somehow you get out over the bar by accident.

If you have a fluxgate or other accurate heading reference just aim your bat along a steady course starting at say 000 until you see where the Maganetic one settles down, ten do this for several other points of the "compass" and work out what the difference is if there is not a set pattern that you can remember then you should make a note of it.

I have yet to see a magnetic compass that is easy to follow in a fizzboat so wish you luck with this.

I have Suunto handheld compass that I brought with me from NZ and have found recently that it seems to work just fine when I used it to assist in setting up a couple of SAT TV dishes in Nthn Europe.

If you want to set up your magnetic compass properly find yourself a Compass Adjuster in Auckland and get them to do you a proper survey and deviation card.

http://www.selfmadesailor.com/index.htm?compass.htm&2

http://www.pangolin.co.nz/c-swing.php

Hi,

I think you should brush up on your navigation theory before giving out advice like this.

It is the Variation that changes annually and from area to area not the deviation.

Deviation is affected by the irons and structure in the boat the compass is on not by the area it is in.

Hi,

Once again I am surprised by your answers.

How do you "adjust" for variation?

Is not still part of the acronym TVMDC- Timid Virgins Make Dull Companions or True, Variation, Magnetic, Deviation, Compass?

When using a Magnetic compass for real you usually have to work this little equation backwards to get the true bearing.

When I was learning I was also told that you should also regularly take Azimuths to confirm the accuracy of the Magnetic Compass as a whole.

what's in its mineral spirits.

Hi,

Don't be so sure.

Here is Post No two of this thread in case you didn't read the link

http://www.yachtforums.com/forums/44891-post2.html

Thanks guys - not immediately concerned with the issue of 'swinging' the compass to correct for variation due to extraneous metal-related forces nor geographical deviation in that similar context. I have the deviation card -somewhere! That's another story perhaps.

As mentioned I am able to correlate with the GPS on various headings and can adjust/record variation and deviation as in 'swinging'. My query really is that I have seen people with "Northern Hemisphere" handhelds and being told that the imbalance of the needle when used in the far South can cause a 'catching' of the needle which tilts quite a lot and whether this 'extra' error causing factor could also be apparent for Northern fluid filled compasses? Intuitively I think not as the range of tilt in a fluid filled compass seems far greater than the needle has in a slim handheld but I thought I would ask the wise ones.

By the way Kiwi, I can agree that magnetic compasses on a bouncing fizz boat are very much a fall back system these days especially with GPS.

I admit that I have gone over the Kaipara Bar quite deliberately, no accidental crossings as yet, and that it itself is an adventure even in decent conditions - up to 10 metre breaking Tasman Ocean SW swells and 6 knots of tide if you were otherwise stupid about weather or don't pick your tide times! I think the wreck tally at the Graveyard/North Head was something like 100 ships in a 100 years until it was closed as a NZ port of entry. Reputably the biggest harbour in the Southern Hemisphere but no lights or official nav buoys at all these days - good fishing for the good keen bloke/sheila though.

I believe you mean mineral oil.

Somewhere I read it was mineral oil, however have no reference to that.
Google yields a variety of discussions. From alcohol, to ethanol, to oil.

My guess- snake oil.

According the FAQs on Ritchie Navigation (http://www.ritchienavigation.com/service/faq.html) site:

"Until 2001, all Ritchie compasses (see exception) were filled with odorless mineral spirits. Ritchie now uses a fluid called Isopar L® that has similar properties but some added benefits over odorless mineral spirits. These can be mixed together.

Exception: Some old style Flat Top Compasses used a mix of isopropyl alcohol and water. This process was stopped in the 1960s. If you have a Flat Top Compass, it is recommended that you test the fluid to see if it is odorless mineral spirits or isopropyl alcohol."

FYI - Isopar is the brand name for a series of products from ExxonMobile.

Hi,

Blair- I agree that there isn't anything like the Kaipara elsewhere mores the pity.

When we were kids we used to get out over the Manukau Bar with my Dad quite often and it could be pretty hairy there sometimes too.

I was out in the Kaipara last December just inside the entrance over on the Baileys Beach side and we (2 blokes) caught our snapper quota in less than an hour along with a couple of pesky sharks.

I subsequently kite fished and surf casted on Muriwai, 90 Mile, Ahipara and Ruakaka with nothing like the same results.