Deviation Card ... do you ?

[thinwater]

Until I bought my first GPS, about 30 years ago. It was not a chart plotter, just speed, bearing,, and lon/lat. But that was still a miracle that felt like cheating.

 

[prestomg27]

Given the accuracy that i can hand steer a course in a heavy sea is more than +- silly degrees i use the compass with a guide along with the chartplotter and gps tracks/course

 

[dunedin]

No. We were well into our second season, and nearly 5,000nm logged, before I realised we never take the cover off the ships compass.
Only used very rarely - eg in very thick fog in very strong tide swirls just inside Corryvreckan, when needed to work out which way being spun.
Generally we navigate visually to next island/headland, and if offshore use digital compass (big digits on display much easier to use).
Hand bearing compass also carried which are generally considered less subject to deviation.

 

[Chiara’s slave]

No. We were well into our second season, and nearly 5,000nm logged, before I realised we never take the cover off the ships compass.
Only used very rarely - eg in very thick fog in very strong tide swirls just inside Corryvreckan, when needed to work out which way being spun.
Generally we navigate visually to next island/headland, and if offshore use digital compass.
Hand bearing compass also carried which are generally considered less subject to deviation.

I sincerely hope our hand compass isn’t. I generally stand on a float and hold the shroud if I’m using it, which must be at least 12ft from anything ferro or electrical.

 

[Skylark]

My boat has two wheels and two steering compasses. A compass deviation card had been created for both by the commissioning dealer when I bought the boat.

Using the ubiguitous Iris 50 handheld as a reference, I like to check and compare to the deviation card once per season.

 

[jlavery]

Planning to, if we actually have much deviation when I get round to checking. I'll check it against the autohelm heading, i.e. electronic compass.

Electronic compass has already been auto-swung, and then verified by observing that overlaid radar echos (radar taking ship's head from autohelm) are directly over the relevant artefact on the plotter chart.

Made a nice deviation card for our Reactor 25 when we were living in New Zealand 35 years ago, by taking opportune bearings as we sailed.

Meanwhile, on Arpeggio, wondered why we veered wildly off course one day while I did some maintenance. Something to do with operating the battery drill next to the saloon table, which houses the electronic compass!

 

[Boathook]

I considered doing a deviation card but have found the compass overall reasonably accurate over the years and it seems to agree with the autohelm compass. Like other posters a main problem is the person on the helm.

 

[johnalison]

I considered doing a deviation card but have found the compass overall reasonably accurate over the years and it seems to agree with the autohelm compass. Like other posters a main problem is the person on the helm.

That is OK until errors add up and lead to trouble and I don't think that accepting small errors as normal is good seamanship. A handbearing compass is only free from errors if it is properly sited, though errors should be small in normal use. It is usually recommended to sight along the boat's fore-and-aft line from well away from the boat to be absolutely sure when checking the main compass, but in practice I just average out a number of measures.

 

[Refueler]

The use of a HH compass to determine deviation is a stopgap method when nothing else is available ... it relies on you having the HH far enough away from influences.

The best is transits .....

 

[Roberto]

I made one, once, mostly for fun, max difference was 3-4 degrees.

Has anyone made a deviation card for the fluxgate compass ?

 

[Concerto]

On my first boat I fixed a fire-extinguisher bracket too near the compass and gave it 14 degrees of deviation. The compass was a Sestrel Minor and I bought a small book on compass correction. The principles are fairly simple and for a small boat dealing with coefficients A & B, ignoring C,D , E and heeling error was sufficient and gave correction to within a degree. I don’t doubt that to do it properly on a more complex boat is a job for pros though. Since then I have never done a card but have occasionally used a hand bearing compass from outside the boat just to confirm that any errors are minimal.

No deviation chart for either steering compass or electronic heading for the autopilot. Last year I discovered why my autoplit sometimes changed direction without me touching it. This short video shows the problem and solution.

 

[srm]

Yes, when I ran a charter yacht. I would do a full swing each spring using the shadow pin on the compass card and the sun. Just had to get a clear evening with the sun low enough, it did not take very long and only needed two sun bearings to be calculated for start and end of swing. This was pre-GPS and as hull and deck were steel a hand bearing compass was useless so the main compass was also used for taking navigation bearings.

Since then, no. When I returned to sailing my own boats GPS was established. We use the cockpit compass as a steering guide/confirmation once plotter vector shows required ground track. This has not been a problem over quite a few thousand miles of coastal, offshore, and ocean sailing.

 

[Poignard]

I have a Sestrel grid compass which is well away from anything magnetic. Seems to provide sufficient accuracy for my needs.

 

[Refueler]

Fond memories of Pelorus and College Yacht Tectona in West Country ..... checking the Dev card ..

 

[srm]

On m YM Instructor course I was on the helm, at night. There was a convenient distant shore light to aim for, but I would check the compass every now and again. The Examiner came in to the cockpit. I quietly asked him to remove the magnet from his pocket. He was indignant at first, then realised he had his camera's light meter in his pocket.

 

[lustyd]

You can imagine there was a bit of "WTF??" going on till I figured it out!

I had a very similar moment when I for some reason looked down at a hand bearing compass once instead of using it properly. My brain then tried to compensate and the main compass started to look wrong too and all seemed right with the world because I was reading two compasses backwards! It's amazing how the human brain works so hard to make things seem right that it takes even longer to get it to work out what's up.

 

[[194224]]

I inherited one with my boat but probably 20 years out of date. No worthwhile variation here.

The question concerns deviation not variation.

 

[William_H]

Just out of interest the requirements for aircraft compass deviation adjustment and correction card. (prior to GPS being so popular) Compass swing every 3 years with engine running radios on. In the case of single engined aircraft swing compass after engine change or overhaul. This latter due to proximity of engine to compass. (engine steel parts are tested for cracks using magnetic field which is supposed to be neutralised but may not be) The compass almost always mounted high on the wind screen away from instrument panel. Generally away from any other portable influence.
For us amateur boaties there are no requirements. Plus of course GPS has made navigation much less dependant on ded. reckoning.
One interesting question relates to proximity of engine to compass. In theory if the engine is under the compass then it can effectively be to the left or right of compass when heeled over. This could make a difference to deviation. Especially if compass has been adjusted to allow for engine influence. Does this matter to deviation in the real world? ol'will

 

[Buck Turgidson]

I started making one using the BG heading sensor which I spent some time calibrating but I found that putting my hand mic up in the cockpit where I like to keep it meant the deviations were different when there was radio traffic and it varies depending where exactly the hand mic is so I've relegated my sestrel to decorative duties only. I can read heading on my Triton 2 Nav instrument and the sensor is fixed on deck well away from anything that will change its deviation. Of course if the electrics went down I would use the mag compass.

 

[MADRIGAL]

The principles are fairly simple and for a small boat dealing with coefficients A & B, ignoring C,D , E and heeling error was sufficient and gave correction to within a degree.

Fresh from a navigation course, I was keen to make a deviation card. While removing most of the compass error on N-S and EW courses using the built-in compensation magnets, I found that the compass card was marked in 5-degree increments. I couldn't find a course which had more than 5 degrees of deviation, so I gave up the project. johnalison's correction to with a degree would be more than enough for me; I'm lucky if I can steer my small sailing boat within 5 degrees of a course in any kind of a seaway.