Deviation Card ... do you ?

[AntarcticPilot]

I do and I don't! My main compass is a fluxgate one linked to the navigation electronics. This constructs its own internal deviation table during setting up, which involves steering in circles. So I don't have a printed deviation table, but the compass has one internally, which it applies to the readings automatically. I also have a magnetic bulkhead compass that is mainly a backup. That doesn't have a deviation table, but I do check it against the fluxgate compass from time to time and have never noticed a significant error.

I note that an error of a degree or two is probably immaterial to us on small craft; we are very unlikely to hold a course or take bearings with that accuracy.

 

[Refueler]

I do and I don't! My main compass is a fluxgate one linked to the navigation electronics. This constructs its own internal deviation table during setting up, which involves steering in circles. So I don't have a printed deviation table, but the compass has one internally, which it applies to the readings automatically. I also have a magnetic bulkhead compass that is mainly a backup. That doesn't have a deviation table, but I do check it against the fluxgate compass from time to time and have never noticed a significant error.

I note that an error of a degree or two is probably immaterial to us on small craft; we are very unlikely to hold a course or take bearings with that accuracy.

I challenge anyone with a typical boaty compass to steer to or take bearing correct to one degree ..... its always a compromise averaged .... based on - that'll do !

 

[jamie N]

Concerto's problem in #31 was the same as I had in a one man submarine, which was controlled by foot pedals. An "engineer" had replaced the aluminium toecaps on the pedals with steel ones from a RedWings safety boot, and not told anyone.
The gyro was in between the 2 pedals......... .
The "engineer" added to his helicopter airmiles going back to the beach the very next day, and we converted the pedals back to standard.

 

[Momac]

In addition to the MFD and a back up tablet I have two magnetic compasses plus a hand bearing compass on my boat. I know with certainty that none of the magnetic compasses are precisely correct.
I only use the magnetic compass to keep a steady course as it can be easier on the eye than the MFD. So don't feel any need to consider the compass to be a precise instrument.
But all depends where folks expect to go boating and whether there is any fear of reliance on electronic devices

 

[oldgit]

Being merely a coast hugging hobby boater have only once ever used a compass in anger.
Cruising along along the North Kent coast on autopilot looking for the Copperas / Reculver bouys when a mist descended.
Whitstable Harbour became dimly visible on the bow, it should have been well out of sight to starboard.
Something wrong perhaps ? for want of something better to do turned off the auto pilot.
Fortunately had put a few waypoints with compass heading on my paper charts.
There followed an interminable hour more or less holding a compass heading while keeping a very close eye on the depth sounder before the relief of seeing one of the bouys.
Nor sure if sticking ones head out of the window and anxiously listing for anything coming the other way really helped.

The only positive , the reassuring fact that due to having less than 15-20 feet of water under your keel, you were more likely to go aground than bump into anything big or expensive.

It later turned out the fluxgate had failed.

 

[Alicatt]

No, being on a canal it's all relative, you can only go where the banks take you

 

[Porthandbuoy]

No deviation card. I compare my magnetic compass when underway against the GPS Navigator (displaying magnetic) and it's within a few degrees on all points of sail. There are 4 adjusting magnets (or are they iron rods, I don't know) below the compass. I've never touched them and wouldn't know where to begin.

 

[RupertW]

No deviation card. I compare my magnetic compass when underway against the GPS Navigator (displaying magnetic) and it's within a few degrees on all points of sail. There are adjusting magnets (or are they iron rods, I don't know) below the compass. I've never touched them and wouldn't know where to begin.
View attachment 168896

GPS and magnetic always roughly agreeing seems extraordinary unless you are in an area with few tides or currents or you always go exactly with the current or exactly against it.

 

[Mudisox]

I swing my compass every year, and also check the auto pilot heading with main compass before a big crossing, I often find that the occupier of the guest cabin has put a magnetic "something" close to the autopilot compass.

 

[Porthandbuoy]

GPS and magnetic always roughly agreeing seems extraordinary unless you are in an area with few tides or currents or you always go exactly with the current or exactly against it.

In the Firth of Clyde and off Aran. Minimal tidal influences. But as I said "within a few degrees". Totally different scenario when you head round the MoK and head for the the likes of Islay, Mull, Jura, Gigha and all points N & W.
I remember many years ago, sailing from Barrow to Glasson and my son, about 10 at the time, asked "Where are we going dad?"
I pointed off to port, "Over there son. Glasson dock."
"Well why are we going this way?" he said, pointing out into the Irish Sea.
There then followed a long conversation with sketches, about tidal vectors, leeway and the difference between True and Magnetic North. Thirty years later he still remembers that 'lightbulb moment' when it suddenly clicked in his head and it all made sense. Wouldn't have worked in a classroom environment, but because we were doing it for real, and he could see the effects, it all made sense.

PS. can I just add, the main reason for comparing the magnetic compass with the GPS heading is in case someone has left an oil can, a magnetic screwdriver or a pair of pliers near the compass (see pic)! Mobile phones and small change will also mess with your magnetic compass.

 

[Roberto]

has put a magnetic "something" close to the autopilot compass.

My fluxgate is near the engine, when I start the engine the pilot ram gives a distinctive "bump" on one side, quite possibly the magnetic field created by the alternator starting to charge.

 

[capnsensible]

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.

Apart from the shroud....

 

[Chiara’s slave]

Apart from the shroud....

Does stainless affect compasses? It’s non magnetic, I had thought not. And it’s not a great deal of material.

 

[AntarcticPilot]

Does stainless affect compasses? It’s non magnetic, I had thought not. And it’s not a great deal of material.

Depends. I think the ones in common use (300 series) on boats aren't, but not all stainless steel is non magnetic.

 

[Chiara’s slave]

Depends. I think the ones in common use (300 series) on boats aren't, but not all stainless steel is non magnetic.

I was aware that not all is non magnetic. The grade for rigging wire is though.