Compass spinning problem

[Bill Fletcher]

The compass on my CD 27 spins (i.e., rotates) whenever I am underpower and accelerate beyond approx. 60 or 70 capacity. Has anyone experienced this problem? Any suggestions on how to remedy it?

Bill
"Sandra Marie"
CD'27



fletch@loa.com

[BSinskie]

Bill,
If I read/interpreted your question correctly you say that when you run your engine at or close to maximum reccommended RPMS the compass deviates. How much does the heading change when you speed up the engine? Maybe your alternator is creating a magnetic disturbance. That is the best guess I have, how to correct it I don't know.

(Before I get slammed, just kidding about the who needs a compass when you have GPS)

[Larry DeMers]

Hi Bill,

Well, of course your compass should not be doing this. You have my engineering interest on this problem. Could you provide more info on this please?
What compass do you have and where is it mounted?
Is it lit with a night vision bulb? (ie:Is there 12vdc running to it?)
Is there wiring in and around the area where the compass is located//within 3 ft. anyway?
By 60 to 70, do you refer to percent of max. HP or what?
Has it always done this, or is it only recently?
If only recently, have you added any electronics or wiring to the boat?
Have you associated the spinning with a specific RPM, or is it happening whenever the engine runs, but gets worse when it reaches 60-70% of power? In other words, what else is happening when this occurs?

In theory and in fact, current passing thru a conductor will create a magnetic field. The field is proportional to the current in the conductor, and the polarity of the field depends entirely on the polarity of the current in the wire..ie: if the current is flowing from end A to end B or vice versa. A compass would need to be within the sphere on influence of the field to be affected, and this is usually stated as about 1 meter. The other possibility is that vibration is getting to the compass card, setting up resonances in the card itself, causing it rotate. If this were the effect happening, I would exppect to see the card reverse rotation at some frequency too.

How old is the compass, and is it in good condition, with the proper amount of fluid in the bowl?

Shoot some answers to me, and I'll think on it a tad.

Cheers,

Larry DeMers
s/v DeLaMer
Cape Dory 30

The compass on my CD 27 spins (i.e., rotates) whenever I am underpower and accelerate beyond approx. 60 or 70 capacity. Has anyone experienced this problem? Any suggestions on how to remedy it?

Bill
"Sandra Marie"
CD'27

demers@sgi.com

[Anthony P. Jeske]

Bill:
I suspect it's a vibration induced event. You can easily verify this by detatching the compass from the bulkhead and revving up the engine. If in fact it is vibration, the fix wil be easy also.
Let us know how this turns out.
Good Luck
Tony Jeske
CD-25D #141
San Diego



ajeske@ixpres.com

[Bill Fletcher]

Hi Larry,

Here's what I can recall (she's been on the hard for merely a few months and already my memory is fading): While I don't recall the type of compass I have (shameful), I do recall that it is mounted on the starboard cockpit bulkhead (I'm assuming orig. equipment for a 1977 CD'27); the compass has a night vision bulb and to my knowledge there is no other wiring around the immediate area, and I've made no recent electronic upgrades; when I referred to "60 to 70" I meant to say approx. 60 to 70 percent of recommended maximum RPMs (my best guess), and I only notice the compass spinning/rotating when the engine is accelerated to that range, otherwise the compass seems fine; this past season was my second season sailing her, and I noticed the problem about halfway through the season--which is, of course, not to say that the problem hasn't been around for some time earlier.

As to the amount of fluid in the bowl, I'm clueless, but would be interested to hear how you check and maintain the appropriate level of fluid.

Hopefully, you can point me in the right direction (sorry, it had to be said)!

Bill
CD'27
"Sandra Marie"

Hi Bill,

Well, of course your compass should not be doing this. You have my engineering interest on this problem. Could you provide more info on this please?
What compass do you have and where is it mounted?
Is it lit with a night vision bulb? (ie:Is there 12vdc running to it?)
Is there wiring in and around the area where the compass is located//within 3 ft. anyway?
By 60 to 70, do you refer to percent of max. HP or what?
Has it always done this, or is it only recently?
If only recently, have you added any electronics or wiring to the boat?
Have you associated the spinning with a specific RPM, or is it happening whenever the engine runs, but gets worse when it reaches 60-70% of power? In other words, what else is happening when this occurs?

In theory and in fact, current passing thru a conductor will create a magnetic field. The field is proportional to the current in the conductor, and the polarity of the field depends entirely on the polarity of the current in the wire..ie: if the current is flowing from end A to end B or vice versa. A compass would need to be within the sphere on influence of the field to be affected, and this is usually stated as about 1 meter. The other possibility is that vibration is getting to the compass card, setting up resonances in the card itself, causing it rotate. If this were the effect happening, I would exppect to see the card reverse rotation at some frequency too.

How old is the compass, and is it in good condition, with the proper amount of fluid in the bowl?

Shoot some answers to me, and I'll think on it a tad.

Cheers,

Larry DeMers
s/v DeLaMer
Cape Dory 30

The compass on my CD 27 spins (i.e., rotates) whenever I am underpower and accelerate beyond approx. 60 or 70 capacity. Has anyone experienced this problem? Any suggestions on how to remedy it?

Bill
"Sandra Marie"
CD'27

fletch@loa.com

[Ed Haley]

You have had great feedback already and I would only add some similar advice regarding the compass' errant readings. If the needle predictably rotates in one direction when the engine revs increases, I would suspect that the generator is causing a magnetic effect on the corrector magnet's magnetic field in the compass. Larry touched on this in his response. There are also many possibilities for magnetic interference in your bulkhead-mounted compass because of its proximity to electric wiring.

As Anthony suggested, it may be due to vibration but I suspect magnetic interference is playing a role.



eghaley@twcny.rr.com

[Larry DeMers]

Hi Bill,
Well, that eliminates a few ideas I had..heh. Ok, so it is either magnetic influences being felt at higher RPM, or vibration from the engine causing the card to rotate on it's own due to resonances from the engine vibration acting on the cockpit bulkhead, which acts like a large sounding board, causing the card to spin one way or the other.

I still favor some wiring carrying a larger than normal current when the engine is cranking out full power (why run that high an rpm?). My bet is that the wire is right behind the compass area on the inside of the bulkhead. Now why would this only act up at very high rpm? Well, the alternator will output more current into a heavy load when the rpms increase, so if there is a conductor that is heavily loaded or poorly grounded (ie: partially shorted making a partial contact with ground..limiting the current ot something under the that circuits breaker trip rating at one end, and being supplied with current from the alt., then as the engine spun up higher, the current would increase, to a point. The associated magnetic field would expand, encompassing the compass, and causing the card to try and align it's north pole at right angles with the direction of flow of the current. Check within 1 meter of the compass's back surface for wiring that may be the culprit.


Cheers,

Larry

Hi Larry,

Here's what I can recall (she's been on the hard for merely a few months and already my memory is fading): While I don't recall the type of compass I have (shameful), I do recall that it is mounted on the starboard cockpit bulkhead (I'm assuming orig. equipment for a 1977 CD'27); the compass has a night vision bulb and to my knowledge there is no other wiring around the immediate area, and I've made no recent electronic upgrades; when I referred to "60 to 70" I meant to say approx. 60 to 70 percent of recommended maximum RPMs (my best guess), and I only notice the compass spinning/rotating when the engine is accelerated to that range, otherwise the compass seems fine; this past season was my second season sailing her, and I noticed the problem about halfway through the season--which is, of course, not to say that the problem hasn't been around for some time earlier.

As to the amount of fluid in the bowl, I'm clueless, but would be interested to hear how you check and maintain the appropriate level of fluid.

Hopefully, you can point me in the right direction (sorry, it had to be said)!

Bill
CD'27
"Sandra Marie"

Hi Bill,

Well, of course your compass should not be doing this. You have my engineering interest on this problem. Could you provide more info on this please?
What compass do you have and where is it mounted?
Is it lit with a night vision bulb? (ie:Is there 12vdc running to it?)
Is there wiring in and around the area where the compass is located//within 3 ft. anyway?
By 60 to 70, do you refer to percent of max. HP or what?
Has it always done this, or is it only recently?
If only recently, have you added any electronics or wiring to the boat?
Have you associated the spinning with a specific RPM, or is it happening whenever the engine runs, but gets worse when it reaches 60-70% of power? In other words, what else is happening when this occurs?

In theory and in fact, current passing thru a conductor will create a magnetic field. The field is proportional to the current in the conductor, and the polarity of the field depends entirely on the polarity of the current in the wire..ie: if the current is flowing from end A to end B or vice versa. A compass would need to be within the sphere on influence of the field to be affected, and this is usually stated as about 1 meter. The other possibility is that vibration is getting to the compass card, setting up resonances in the card itself, causing it rotate. If this were the effect happening, I would exppect to see the card reverse rotation at some frequency too.

How old is the compass, and is it in good condition, with the proper amount of fluid in the bowl?

Shoot some answers to me, and I'll think on it a tad.

Cheers,

Larry DeMers
s/v DeLaMer
Cape Dory 30

The compass on my CD 27 spins (i.e., rotates) whenever I am underpower and accelerate beyond approx. 60 or 70 capacity. Has anyone experienced this problem? Any suggestions on how to remedy it?

Bill
"Sandra Marie"
CD'27

demers@sgi.com

[Mark Yashinsky]

Do you have any problems w/ your batteries overheating or boiling dry??? Source of high current might be a stuck regulator. Do you have a tach, whose wire goes near the compass??? If this were engine vibrations, do other things in the galley or do the cockpit locker hatches vibrate??? If its enough to affect the compass, you should be able to feel it.

[Bsinskie]

I have read in my owners manual that a diesel engine should be run at 80% max rpms, (in my case the max is 3200 so I run at 2500, and there is a governor to prevent me running over 2500) and that the engine should be sized for the boat so that it only takes 80% to achieve hull speed. I have also been told that it should be run at 80% to prevent carbing up. have I been told the wrong info?

[Bill Fletcher]

No, I haven't had any problems with the batteries and don't have a tach--I do get some engine vibrations.

Thanks for the responses. You've all armed me with some good information.

Bill
"Sandra Marie"
CD'27



fletch@loa.com