fluxgate v traditional compass variation

[stefan_r]

Are fluxgate compasses any less susceptible to local magnetic fields (engines etc) than traditional compasses?

I want to invest in a good quality hand bearing compass and am not sure which way to go.

I have a motorcruiser with twin diesels and therefore want to avoid local variation.

Cheers
Stefan

mailto: stefan@athito.com

 

[AndrewB]

Fluxgate compasses sense the magnetic field and so are just as susceptible to variation as are conventional compasses - also to deviation for that matter, so beware if your boat is steel.

Gyro compasses eliminate variation, but are unsuitable for small boat use.

 

[stefan_r]

ahhhh okay...suggestion for handheld?

I am after a decent handheld compass - any suggestions, from what I see (price not included) there isn't much of a difference between electronic and card compass.

What have you got?



mailto: stefan@athito.com

 

[Twister_Ken]

Re: ahhhh okay...suggestion for handheld?

With an h/b compass there should be less problem with boat induced deviation because you have the choice of where to use it, and can pick a place as far from iron and steel lumps as possible. It's worth experimenting on your own boat to find such a spot (which is also safe to work from).

As to fluxgate or trad, the electronic ones sometimes come with nice extras like being able to memorise bearings, so you don't have to write them down. OTOH, there's very little to go wrong with a trad compass, so maybe it's swings and roundabouts.

FWIW, mine is a trad 'hockey puck' mini compass, from Plastimo.

But a more intersting question might be how often nowadays do people use h/b compasses. In my case, it's usually only to take anchor bearings.

 

[AndrewB]

Re: ahhhh okay...suggestion for handheld?

A fluxgate handheld of the Autohelm type is great for taking bearings, just point and shoot. But it's poor for some other purposes, e.g. running down a course holding a constant bearing on a waymark (of course, we do that with GPS these days).

All handhelds are quite useless on my own boat, since it is steel.

 

[Guest]

Deviation should not be a problem with either compass as long as you are sensible about where you use it. I understand however that you have to be careful to keep the electronic ones horizontal when taking bearings.

The memory and the "snapshot" abilities are the only advantage of the electronic ones. With practice it is just as quick and easy to use a trad. compass and for inshore pilotage these are the only ones that are any good. I've been an instructor with my own school for over ten years and we use h/b's a lot - we take a few fixes but the Scottish west coast requires a lot of careful pilotage!

I can recommend the Plastimo Iris 50.

 

[LadyInBed]

What about Binoculars?

I hardly ever use my HBC (I normally use transits when I’m anchored). I have often thought that Binoculars with a built in compass might be a better idea. Has anyone any user experience?

 

[hugh_nightingale]

Re: fluxgate v traditional HANDHELD

The request, I believe, was for a handheld - traditional or electronic.

As they are both "compases" they will both suffer the same way from any near magnetic material, either on the boat itself or in the earths surface.

Therefore, as noted by other posting, you will need to find a suitable place on your own boat where there is least deviation. Both are just as good for taking hand bearings. Both have to be held near horizontal, in fact some fluxgate compasses have in built tilt compensation so are better than trads.

The advantage of electronics is the memory, again as noted somewhere else.

Do note that the fluxgate has other errors, both fixed and cyclic. These are caused by the ferrite or other magnetic material used and the orthogonality of the sense coils. The beauty of electronics, if you pay enough, is that these can be detected and stored in a deviation correcting table, you may even be able to do your own, regular, calibration.

You have to rely on the traditional compass having an accurate scale, it could just as equally have marking errors. However, we have found the Iris 50 very good.

You still have to rely on the mark one eyeball.

 

[Twister_Ken]

Re: What about Binoculars?

Nigel,

I've used them, They are a delight in daylight when you can see what you're looking for and if the sea is relatively smooth. Bins for bearings is really a two handed operation so you can't easily take a bearing whiile hanging onto a shroud, for example. Also when it's rough it can be difficult to keep the object in the right place for long enough for the card to settle.

Bins are useless at night if you're looking for a flash. If it's not in the field of view at flashing time, you don't see it. At least with a handbearer, you've got much broader vision and will see the flash, even if you don't get lined up for a bearing on it in that cycle.