Deviation Card / Table?

[jackdale]

How many of you have a deviation card / table on your boat? I have sailed about 40 different boats. Four had deviation cards / tables. Yes, many of them had deviates on board too. ( I had to get that in first)

[cal40john]

Yes I have made one. Cruising in Puget Sound I've never bothered to use it. Some say using the GPS to create a table is flawed, but I did it on a lake, windless day, autopilot steering a constant course on each of the headings, went back on a couple of the headings to check repeatability.

Made one and used it on my trip to Hawaii on a Cal 34 many years ago.

John

[JiffyLube]

I've compaired my compass to the chartplotter, and they are very close to agreeing on all points of sail.

[MarkJ]

We don't even use the compass very often.
It basically agrees with the GPS and Fluxgate compass on the Auto Pilot. I only use it when hand steering (an hour a day or so) or when things get whacky in a squall.

with the 3 all being slightly different all the time I guess we just mentally allow for it

Mark

[Stillraining]

If I was crossing an Ocean I would ..no need in PNW to concern ourselfs...currents will mess with you around here way more then a bit of deviation is going to...got to love them GPS for quick VMG's...I glanced at my compass now and then just to feel nautical...and make a mental note Im still headed away from home or back to it.

[jackdale]

So is the deviation card going the way of the sextant?

As a coastal navigation instructor, I devote an entire evening to variation, deviation and the ship's compass.

How many out there have calibrated their fluxgate compass, so that deviation is not (should not be) a problem?

We recalibrated the one on the teaching boat after the rudder sensor was reinstalled after it came unglued.

Jack

[Connemara]

Voted yes, created it myself, but that's a bit of a stretch... I have a list of deviations for about half a dozen angles, which I put together last summer. But it's not complete and the data is still in the back of the log, rather than on a nice laminated card.

If there had been a category called 'working on it' that's what I would have clicked.


Connemara

[Cheechako]

probably less of a necessity with GPS now, however, if you just use your GPS to create a general one you might find that you are off significantly on certain headings... usualy due to some other part of your boat. This is good to know.

[Vasco]

With the advent of fairly cheap fluxgate compasses most folks don't bother anymore. I compare my magnetic compass to the fluxgate on my autopilot as it's not a bad habit to get into. I also have a hand bearing compass that is a fluxgate compass so that can be used in a pinch. I would not bother unless being struck by lightning and then you'd need the compass swung and corrected anyway.

[nautical62]

Originally Posted by JiffyLube

I've compaired my compass to the chartplotter, and they are very close to agreeing on all points of sail.

I also checked with the same results and decided that any small deviation there may be was not significant to my navigational requirements.

[David M]

I agree that for smaller vessels, a deviation card is probably unnecessary. The margin of error for steering a smaller vessel is so great that probably most of the time it is greater than the deviation error. You should have some idea though how much your deviation error is. If your Ships Compass error is 10 or 15 degrees at times, then yes, that's significant and you need to know that.

For ships, its a different story. They need their cards since they can be steered to within a few degrees depending on the sea state...although they do use gyro's. Gyros can fail and obtain gyro error as well.

I don't think its a wise idea to think that GPS replaces a compensated compass with a deviation table. GPS is not fail safe. The Earth's magnetic field is fail safe...the DOD cannot turn it off at will.

[Captn_Black]

Originally Posted by David M

The Earth's magnetic field is fail safe...

This isn't always true....
But most areas where it's not are marked on charts...

[GordMay]

Originally Posted by David M

... The Earth's magnetic field is fail safe...

Maybe not - think pole reversal and/or geomagnetic shift, not to mention variation.

[maxingout]

I have checked deviation as a navigational exercise, but I never used it in practice. When sailing offshore, we go with the winds, and I don't need a deviation card to get from the Canaries to the Caribbean.

I use my compass to get a general idea of heading, and I use a handheld compass when it's necessary to enter a pass on a particular heading. The handheld compass is suspended away from major magnetic influences, and so mostly I take only variation into account when sailing through pases and entering ports.

[GordMay]

Let’s not confuse Variation with Deviation.

The effect of Variation is the same for all boats in the same area at the same time.
Deviation is specific to the boat and the course it is sailing on, and varies with the boat's heading. For each course we steer, there will be a different deviation to apply - hence the deviation correction card.

Variation (Declination):
Magnetic variation is the difference between True Bearings and Magnetic Bearings and is caused by the different locations of the Geographic North Pole and the Magnetic North Pole, plus any local anomalies such as iron deposits. Variation is the same for all compasses in the same location and is stated on charts, along with the date it was measured and annual rate of change.

Deviation:
Magnetic Deviation is the difference between Magnetic Bearings and Compass Bearings. Deviation varies for every compass in the same location, and depends on such factors as the magnetic field of the boat. The value will also vary depending on the orientation of the boat. Magnets and/or iron masses can be used to correct for deviation so that a particular compass will accurately give Magnetic Bearings. More commonly, however, a deviation correction card will be drawn up listing errors for the compass which can then be compensated for arithmetically.

Goto:
Navis.gr - How to apply the Compass Error