I installed a new Ritchie compass on my Hunter 45CC boat. It has a 10 degree deviation. How can you correct the deviation? The crew at the bottom did not work! Any idea? Thanks, Viktor
Compass deviation
- Thread starter Viktor Eysselein
- Start date
Deviation is complicated, and has a lot to do with the magnetic field of your individual boat. You may be able to send it in to have some of the deviation taken out of it, but like I said, the deviation has much to do with the field of your boat.
Deviation is usually not consistent across all 360 degrees of the compass. It changes at each heading. Sailors that are serious about their manual compass make a “deviation card” - recording the deviation from your actual magnetic heading at major bearing points. You can do this by comparing your GPS heading with your compass (be careful about wind and current if you’re doing it this way). Even better, you can line up two, fixed objects by site (find their heading on your chart), and read the deviation out that way. The GPS way is a whole lot faster.
My compass is off by as much as 8 degrees.
Also, be careful about true (T) heading vs. magnetic (M). This is called variation and it changes depending on where you are on the globe. Nautical charts will show the variation on the compass rose.
Deviation is usually not consistent across all 360 degrees of the compass. It changes at each heading. Sailors that are serious about their manual compass make a “deviation card” - recording the deviation from your actual magnetic heading at major bearing points. You can do this by comparing your GPS heading with your compass (be careful about wind and current if you’re doing it this way). Even better, you can line up two, fixed objects by site (find their heading on your chart), and read the deviation out that way. The GPS way is a whole lot faster.
My compass is off by as much as 8 degrees.
Also, be careful about true (T) heading vs. magnetic (M). This is called variation and it changes depending on where you are on the globe. Nautical charts will show the variation on the compass rose.
Check in your local area for a compass tech. The deck should be able to correct " local" interference from electronic and other boat gear and issue you a Deviation Card... after all neutralization, in my area there is a 17 degree deviation between True and Magnetic North....
Hi sailme88 - not to be a stickler but it's important since both corrections have to be applied to a magnetic compass when you convert from a magnetic heading to a true heading. The compass tech will issue a deviation card, and the local variation is 17 degrees. Both the variation and the deviation have to be taken into account to adjust your course into a true heading.
Here's an article on it with instructions:
The Difference Between True and Magnetic Heading - airplaneacademy.com
You’re flying along and ATC instructs you “turn to heading 220” and so you turn your plane until the numbers on your screen or instrument change, but what exactly are you heading towards? Why do we use two methods of showing our choice of direction and where did it all begin? Or more...
airplaneacademy.com
We're in roughly the same area, our variation is about the same. I'm on the Piscataqua River.
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Of course the Professional Mariner article is talking about more sophisticated compasses used by professionals. A Richie compass, which you can buy at Walmart, on a sailboat doesn't need that treatment. Remember that you probably can't tune out all the deviation but you can reduce it to minimal or insignificant. Insignificant means that it is little enough to be within ones ability to steer a course - like 5 degrees. "Though I have to admit that modern auto pilots do a good deal better than that. Of course variation you can't do anything about except move to an area with less of it.
If you haven't already read this:
If you haven't already read this:
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,131
We grow up thinking, Life is simple and there are constants to rely on.
The North Pole is moving... and has been for years..
Then we begin to wonder... what else is changing.
- The north pole is fixed in the Arctic where Santa has his workshop.
- The weather is the same Winter-Spring-Summer-Fall.
- The Magic 8 Ball is always right.
The North Pole is moving... and has been for years
..Then we begin to wonder... what else is changing.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,131
Yes it is in the sky a far distance from the earth.
Not affected by the magnetic shift of the earths core..
But...
While it is always there...
will it always point "North" as the earth wanders and tilts about on it's path around the Sun?
Not affected by the magnetic shift of the earths core..
But...
While it is always there...
will it always point "North" as the earth wanders and tilts about on it's path around the Sun?
The good news is that magnetic N has gotten closer to true N over time!We grow up thinking, Life is simple and there are constants to rely on.
Then we discover the real world...
- The north pole is fixed in the Arctic where Santa has his workshop.
- The weather is the same Winter-Spring-Summer-Fall.
- The Magic 8 Ball is always right.
The North Pole is moving... and has been for years
View attachment 221894
Then we begin to wonder... what else is changing.
Thanks for that helpful post. Nice to see that at least someONE understands this difference between variation and deviation. Too bad it took so long (not for you to post but that the right answer didn't appear immediately.)Hi sailme88 - not to be a stickler but it's important since both corrections have to be applied to a magnetic compass when you convert from a magnetic heading to a true heading. The compass tech will issue a deviation card, and the local variation is 17 degrees. Both the variation and the deviation have to be taken into account to adjust your course into a true heading.
Here's an article on it with instructions:
The Difference Between True and Magnetic Heading - airplaneacademy.com
You’re flying along and ATC instructs you “turn to heading 220” and so you turn your plane until the numbers on your screen or instrument change, but what exactly are you heading towards? Why do we use two methods of showing our choice of direction and where did it all begin? Or more...
We're in roughly the same area, our variation is about the same. I'm on the Piscataqua River.
Truly frightening that more of you don't get it right off the bat. Using incorrect terms seems to be too prevalent on the internet these days, and getting worse. How about amps and amp hours?
A little research would go a long way for the OP. I keep suggesting books , but what do I know? The internet was originally supposed to help us communicate and do research, now it's just become a place for lazy people to ask others to do their homework for them.
Thanks, Stu. I learned about deviation and variation when I took my Captain's license class. I probably would have made the same mistake had I not been required to take the class by the USCG. Everyone makes mistakes, brother.Thanks for that helpful post. Nice to see that at least someONE understands this difference between variation and deviation. Too bad it took so long (not for you to post but that the right answer didn't appear immediately.)
Truly frightening that more of you don't get it right off the bat. Using incorrect terms seems to be too prevalent on the internet these days, and getting worse. How about amps and amp hours?
I never took any classes. I read Duttons and Chapmans. Each of them covers this BASIC material in great detail.
Yes, Polaris is on the move. However given the distance from earth it will take several life times before we notice.
To go back the OP's question. Inside the compass housing there are 2 small magnets of pieces of iron. A screw attached them will rotate them in the housing to help zero out any deviation. In reality the deviation is seldom eliminated, however it can often be reduced.
Most compass cards are only accurate to ± 2.5° or less. That is more than close enough for most navigation so long as charts are on board and the eyeballs still work, and someone on board learned to navigate without relying on Navionics.
This might help...Thanks for that helpful post. Nice to see that at least someONE understands this difference between variation and deviation. Too bad it took so long (not for you to post but that the right answer didn't appear immediately.)
Truly frightening that more of you don't get it right off the bat. Using incorrect terms seems to be too prevalent on the internet these days, and getting worse. How about amps and amp hours?