Compass location revisited.

[Pat Hurley]

Hi all ... Purchased a used 2007 Marlin back in October and after running a few trips I observed the compass going haywire. Readings were all over the place on the run back in, the compass never seemed to want to settle in on course. Even while tied up in the slip I was observing 30+ degree swings on the dial. There were no electronic devices nearby IE cell phones etc. Later in the week I had my electronics guy over to quote some upgrades I want to install, and he also observed the compass movements. Flash forward I ordered a new Ritchie FN-201. Following the instructions I carefully held the compass pointed in the same direction moving towards the helm and over the factory mounting hole, and as I lowered the compass into position observed a change or variation of 60+ degrees. "WOW" ... So, per Ritchie instructions if the variance exceeds 15 degrees the compass should be located elsewhere ?? Now granted GW mounts all Marlin compasses in the same place on the Marlin centered with the Helm Wheel so what gives ? Could there be that much interference with the helm steering unit ? Because as I move away from the mounting location the compass returns to point in a direction more relative to where I'm facing. I wonder if there is that much adjustment in the compensation rods to make up a 60+ degree variance ??

What say you ? What would be in the helm steering unit that causes such variance and why would GW mount it there ?

 

[wspitler]

What you are seeing is called deviation, the difference between your compass and magnetic north. (Variation is the difference between magnetic and true north.) Of course you've looked for any iron based object near the mounting location. Could be below the mount and out of sight. I'd also turn off all power, AC and DC to see if any wires such as stereo amps, lights, pumps, etc. could be impacting the compass. Before I mounted it, I'd take it away from all iron/magnetic sources and see if it is relatively accurate while away from all metal/electrical influences. You'll need to figure out what it should read with no outside influence to see if it is a compass problem. I'd then go ahead and place it in position using stainless hardware, of course. Then figure out the approximate vessel heading to see how much deviation you have. I would think 60 degrees would be difficult to correct. To adjust the compensation requires that you "swing" the compass. In other words you'll have to rotate the boat thru 360 degrees and make adjustments to minimize deviation on different headings, usually every 15 degrees or so. Unless your boat has been struck by lightning and things have been magnetized, it is unlikely that Grady's normal mounting location is highly affected by the helm and pump. I think that each compass is adjusted with the compensation screws when they leave the factory. Good Luck!

 

[seasick]

It's called declination
I don't think that is the issue. The declination will be relatively constant difference. The compass dial should not be swinging back and forth.
That could be interference but if nothing electronic has changed and the compass worked before, it's probably not electrical interference.
In most compasses, there are compensation adjusters that are small magnets that get adjusted to compensate for magnetic interference. That mechanism may come loose and cause the dial to swing. It could also be a simple and a cellulat phone or other device being too close to the compass.

 

[wspitler]

If the new compass is swinging back and forth in the slip, at rest, then there must be cyclical interference. That model compass does have adjustments for deviation, but I doubt you could compensate for 60 degrees of error. In the past on board vessels and aircraft I have "swung" the compass to develop deviation cards that give the deviation of a specific magnetic compass for the various headings. The FAA requires a deviation card for all Mag compasses for every 30 degrees of heading, with nav lights on. The deviation correction for the different headings are seldom the same. Deviation can be + or _ (East or West). Remember CDMVT where D = deviation and if my memory serves me correct, when going from compass to true, you add East.. Declination is related to astronomy or "declining" something. Since it is a new compass, it is unlikely to be swinging back and forth at rest without some outside influence. As I understood it, only the original compass gyrated.

 

[Pat Hurley]

Thanks for the input....

Boat is currently out of the water, no cell phones nearby and everything is shut off including the batteries. There is a Raymarine 12" Hybrid Touch (soon to be replaced with a Furuno TZT 3) mounted in the display area. As I stated the NEW compass is pointing in the right direction within 5 degrees give or take until it is set into the factory mounting hole which is directly above the steering column. When the compass is lowered into the mounting hole the dial turns approx 60 degrees. It leaves me to believe that the steering column is the culprit impacting the variance. As I lift the compass out of the mounting cutout and move it port or starboard 6 " it returns to a display heading relative to what it should be. I'm going to contact GW tech support to see if they experience this when doing the same

 

[wspitler]

I wonder if your steering system components, hoses, helm etc. have been replaced with a non-standard ones. Or possibly there are things installed nearby like speakers etc. that could be providing that deviation. Most helm components are mostly stainless steel and contain very little iron.

 

[seasick]

Wspitler, You are correct I was w...wro.....wron... Well you know!

 

[SkunkBoat]

It does it with all power off.

it has to be a magnetic item near the mounting location.

That could be speakers in the cabin/head/dash
vfh radio speaker
a non-stainless nut or bolt or washer holding the steering or anything nearby
a screwdriver or wrench in the glove box
Any motor..
... AP motor mounted under dash


..possibly internal components (rotor and pistons) of the helm pump got magnetized? ...possible...maybe....its a stretch... unless you had powerful speakers near it a some point and magnetized it...
If thats the case you need a degaussing coil.

 

[Pat Hurley]

It does it with all power off.

it has to be a magnetic item near the mounting location.

That could be speakers in the cabin/head/dash
vfh radio speaker
a non-stainless nut or bolt or washer holding the steering or anything nearby
a screwdriver or wrench in the glove box
Any motor..
... AP motor mounted under dash


..possibly internal components (rotor and pistons) of the helm pump got magnetized? ...possible...maybe....its a stretch... unless you had powerful speakers near it a some point and magnetized it...
If thats the case you need a degaussing coil.

Good call ... I'm going to try to pinpoint the source with a small handheld compass next visit to the boat. All indications is it 's coming from the steering mechanism.

 

[seasick]

I was going to suggest the small compass. A little cheap one will do and maybe better than a good compass. . Move it around and watch the needle. One end of the needle will point to the magnetic source, By moving to different locations you will be able to triangulate the source. You may also see the tip of the needle lean down or up. That can tell you if you are at the plane of the interference ot hogher or lower.

 

[DennisG01]

Along the lines of what was mentioned above, I'm thinking there is something non-stock added/modded under the helm or in front of the steering wheel. Look around for anything that seems to be an add-on and inspect the hardware that was used. Because you're dealing with a used boat, you're also dealing with the "previous owner" factor and that will be near impossible for anyone, including Grady, to help with since we/they are not there. Suggestions/ideas we can help with - but you'll have to do the majority of the investigative work. But, feel free to post a bunch of pictures of your helm area and inside/behind the helm and maybe we'll get lucky and spot something.

 

[DennisG01]

Oh... just for good measure and possibly "get lucky"... disconnect the negative cables from all batteries and see if the issue goes away.

 

[Pat Hurley]

.... as an update I had purchased a new compass (throwing spaghetti) thinking the old one was bad. It wasn't. Same reaction observed. My belief is the steering unit is the culprit. I had asked the local electronics guy if he had a Degaussing tool ... His response : What's that ? At that point I had nothing to say and just laughed. In the meantime My auto pilot digital readout and GPS compass read outs suffice. I keep a very good Suunto KB compass onboard. The mounted one is for looks only

 

[wspitler]

The cyclical nature is the confusing part. If you are experiencing cyclical deviation with all power sources off on the boat, there must be something external to your boat in that area causing it. Could be nearby radar electrical wires etc. If it does not occur at sea, clear of all possible sources then that’s when you need to align your system and be able to count on your magnetic wet compass.

 

[Fowl Hooked]

My compass hasn't changed but the components around it have and that was my culprit. AP pump on my 265 was mounted under the instrument panel, compass is centerline right in front of the helm and maybe 12-15" from the pump. Pulling the old one out I didn't notice any movement but dropping the new one, and it's apparently much stronger motor, in caused massive movement and my compass now reads 270-330 no matter what direction I'm pointing. As it doesn't sound like you've changed anything else it could be that the new compass is more sensitive to interference and I'd look for anything in the area, many likely causes have been mentioned. Weird that it swings even with no power, if it's magnetic interference I'd have thought it would deviate some number of degrees but then hold fairly steady. Boat gremlins.

 

[Fishtales]

Sounds like gremlins to me Pat. Have you been in the Bermuda Triangle lately?

Can you isolate the compass with metal or something to definitively show it is the location? Do you have access to another like boat? Did you have the prob with the previous compass? Could that model have a unique sensitivity? Just asking as I gave the same model and never observed such issues.

 

[Pat Hurley]

Sounds like gremlins to me Pat. Have you been in the Bermuda Triangle lately?

Can you isolate the compass with metal or something to definitively show it is the location? Do you have access to another like boat? Did you have the prob with the previous compass? Could that model have a unique sensitivity? Just asking as I gave the same model and never observed such issues.

Bermuda Triangle ....hahaha you read my mine Dan. Definitely a head scratcher. Compass(es) work fine until you place them in the mounting hole. I've looked all up in there to see if someone left or dropped a magnetized driver head or something, but have yet to see anything. Best I can tell is somehow the steering mechanism became magnetized. It sits right in line with the compass mounting hole. I would like to try a degaussing tool on it (if someone local to me has one).

 

[seasick]

Was the compass removed or bumped hard when the pump was worked on.
If so , a compensating magnet in the compass may have moved or broken causing the needle to freeze.
To check if that is the case, remove the compass and move it away from the boat.
It should work as you move it around. It may not be accurate though since in theory it was adjusted for the magnetic fields in the boat.
Your new pump may not be magnetically shielded . Test the compass first and if that shows that the compass is good, contact the pump manufacturer for guidance.

One other question; Is the compass frozen all the time or only when the boat is powered?

 

[Pat Hurley]

Was the compass removed or bumped hard when the pump was worked on.
If so , a compensating magnet in the compass may have moved or broken causing the needle to freeze.
To check if that is the case, remove the compass and move it away from the boat.
It should work as you move it around. It may not be accurate though since in theory it was adjusted for the magnetic fields in the boat.
Your new pump may not be magnetically shielded . Test the compass first and if that shows that the compass is good, contact the pump manufacturer for guidance.

One other question; Is the compass frozen all the time or only when the boat is powered?

... No damage. Also as stated I purchased a brand new one, same outcome

 

[Halfhitch]

...and no previous owner installed some neodymium magnets somewhere to hold a door or drawer closed?....just trying to imagine what it could be.

Is there a magnet in a VHF mic hanging nearby? Did someone install an aftermarket steering wheel? ......this is a WTF moment for sure.