Hand Bearing Compass - compensation for dip angle

[cabo_sailor]

Originally Posted by Lodesman

I think you're all taking the piss. Magnetic flux lines are essentially parallel to the earth's surface, except when close to the poles. Unless you're an extreme sailor, it should not matter much.

Could you elaborate that please, excluding the reference to urine?


Sent from my iPhone using Cruisers Sailing Forum

[El Pinguino]

Originally Posted by Lodesman

I think you're all taking the piss. Magnetic flux lines are essentially parallel to the earth's surface, except when close to the poles. Unless you're an extreme sailor, it should not matter much.

Oh no they aren't.......and yes it does ( with a HBC anyway..).

One little aside and this can be seen in the Silva and Plastimo information re 'Zones".

As the magnetic equator isn't the same as the standard 0* equator it follows that dip isn't constant at any given latitude.... ie Dip at 40*S in Bass Strait is not the same as dip at 40*S in South America... this can be seen in Plastimo's definition of zone B and zone C '* Zone B : South Atlantic, Indian Ocean, Central Pacific, Tahiti, Reunion Island.** Zone C : South Pacific, Central and South Australia, New Zealand, New Caledonia.'
If fitting out for global cruising I would be buying a Plastimo Zone B which has no ballast at all.
A zone A compass with ballast under the south seeking needles will be double damned when you go south....

[El Pinguino]

A picha https://commons.wikimedia.org/wiki/F...ation_2010.pdf

A lot of diagrams are very simplistic and do indeed suggest that dip only appears near the poles...

[GrahamHO]

Originally Posted by Lodesman

I think you're all taking the piss. Magnetic flux lines are essentially parallel to the earth's surface, except when close to the poles. Unless you're an extreme sailor, it should not matter much.

No he's not taking the "piss". I am in Ottawa Canada at the moment. I have in my hand an orienteering compass I bought in Auckland New Zealand where I mainly live.
The red north pointer is pointing decidedly down and the needle almost jams on its surround.
We were taught all that at school and did experiments in science. As others have said the lines of magnetic force dip into the magnetic poles and a normal magnetic compass hardly works near those magnetic poles as it would be pointing down as early explorers found. And that is the way they charted where those poles were ( they move )


My cruise at the moment is by B777 and A320. I carry an orienteering compass not for the flight but because the sun is in the "wrong" place in the Northern Hemisphere.
A bit of off topic trivia is that my altimeter equipped Sony phone told me those planes are pressurised to 6,900' when flying at 35,000'

[buzzstar]

[QUOTE=mulangi;1890642 I find that when I use a compass that I bought
Can anyone shed light on this topic.
Thanks,
[/QUOTE]

On reading more of the responses, this is an even better question than it was at first blush. The answers are hugely important, and cumulatively valuable for anyone planning on cruising a fair distance when a compass is or may be important or even vital.

One of the responses notes the difficulty in finding a person to handle the problem even if it is properly recognized. Maybe Cruisers Forum could create a spot for such persons to place their name or business name, address, phone, and email, with the persons using their service (or, unfortunately, others) able to comment on price, rapidity of handling, results, and overall satisfaction. It could be a big help for a lot of folk (including me if I go cruising in the future).

[barnakiel]

We have a Plastimo puck and when we bought ours (around 2003) their website clearly described the zones and the product numbers.

b.

[Wotname]

Originally Posted by buzzstar

…………...

One of the responses notes the difficulty in finding a person to handle the problem even if it is properly recognized. …………..

If push comes to shove one could find the nearest aviation instrument repair facility. Some of these guys regularly adjust magnetic needle compass for dip. Even if they can't handle your marine compass, they will know who can.

[StuM]

If it's hand bearing compass, why not just tilt it up or down slightly while sighting?

[Wotname]

Because on some HBCs, the needle will foul the casing and/or one can no longer see the card properly with the prism viewfinder.

But the method does work in some instances.

[GrahamHO]

One of the responses notes the difficulty in finding a person to handle the problem even if it is properly recognized. Maybe Cruisers Forum could create a spot for such persons to place their name or business name, address, phone, and email, with the persons using their service (or, unfortunately, others) able to comment on price, rapidity of handling, results, and overall satisfaction. It could be a big help for a lot of folk (including me if I go cruising in the future).[/QUOTE]

In Auckland New Zealand I have used a compass expert called Dave.
Phone +649 4453336
That is from my contacts in my phone.
Sorry that's all I have with me and it's a couple of years old but he is / was the acknowledged expert there. I'm not there just now.

[GrahamHO]

Originally Posted by StuM

If it's hand bearing compass, why not just tilt it up or down slightly while sighting?

If it's a hand bearing compass and you are sailing both hemispheres why why not just get 2 hand bearing compasses? A northern and a southern one. Or buy the correct one for your own hemisphere?

[El Pinguino]

Originally Posted by GrahamHO

If it's a hand bearing compass and you are sailing both hemispheres why why not just get 2 hand bearing compasses? A northern and a southern one. Or buy the correct one for your own hemisphere?

Thats why I suggested to the OP at #5 not to chuck his old one....

[GrahamHO]

Originally Posted by StuM

If it's hand bearing compass, why not just tilt it up or down slightly while sighting?

Stu, I've just done an unscientific test with my Silva orienteering compass I purchased in Auckland NZ that I have with me in Ottawa Canada right now. If I put it flat on a table I can rotate the whole compass 360* and the needle rotates with it in other words not working as intended. If I hand hold it and tilt it down (towards north) it is very sticky but will tell me where north is. I think this is because the pivot that the compass pointer pivots on sticks. This is a good quality fluid damped compass. The whole compass needs pointing down around 15* / 20*at a guesstimate to even show about where north is and doing so tends to jam the pivot. If you were trying to sight a headland for example you would be looking at the waves.


I'm no expert but I think that if a compass is compensated for the Southern Hemisphere it would be worse in the North than if it were not compensated at all. But any good compass will be and should be compensated for the hemisphere it was marketed for. I'm sure compass suppliers can deliver appropriate compasses for opposite hemispheres given suitable notice.


My little compass is fine for just telling me where North is at the moment as I'm not using it for navigating. I have a good hand bearing compass back in my boat and I believe it would act in a similar fashion in the north.


I also have a compass on my phone as most people do, but I'm not sure how they work (by GPS??)

[charliehows]

I've got a suunto handbearing compass with an adjustable dip scale specifically for magnetic variation - if you look closely at any decent chart it will show the date the chart was mapped and the add or subtract amount of mag. var. over time - ie how many degrees movement to +/- per year after the mapping date. It can be substantial. My little compass requires a jewellers screwdriver to reset the var. but you can just calculate as you go along.
But -- in the 'taking the piss' dept. - the bloody things hop about so much all the fine measurements are irrelevant. Mostly its 'look out for some bloody big rocks roughly in that direction' is about as accurate as i ever seem to get.

[charliehows]

In the nth sth hemisphere dept. ive used my suunto in the sth is of nz 40ish sth i think, and in the north of thailand 18ish nth - seemed to work as well in either place.