[Dave_E]

Hi All,

I am installing my new plotter next month. Here's the deal. My compass is installed, compass swing every year, no problems with the compass. When I set the plotter where I'd like it to be (permenantly) I get some compass movement (2-4 degrees). My question is can I mount the plotter and then re-swing the compass for acuracy, knowing that I just threw it out of whack with the plotter placement? I don't see why I couldn't... might have to use a correction card more than I'd like.

Dave

 

[Frogwatch]

Whats causing the swing? It is probably the DC input. Maybe use twisted dc input wires.

 

[jerryrlitton]

Hi All,

I am installing my new plotter next month. Here's the deal. My compass is installed, compass swing every year, no problems with the compass. When I set the plotter where I'd like it to be (permenantly) I get some compass movement (2-4 degrees). My question is can I mount the plotter and then re-swing the compass for acuracy, knowing that I just threw it out of whack with the plotter placement? I don't see why I couldn't... might have to use a correction card more than I'd like.

Dave

What you are refering to is compass deviation. Sure, re swing it and if you want to do it right is get a deviation card to mount close to your compass (because you will never get all the deviation out). The card will have every 30 degrees the course you want to the course you steer. For instance 030 degrees steer 032. In addition when you are swinging turn on all the electronics you normally have in operation such as radar, depth sounder and the like. They all can make a difference. Just for grins turn on the auxiliary, the alternator if it is not filtered/shielded may also show some deviation. Also the big belt buckles and swords will cause deviation....

 

[celenoglu]

Deviation is the result of electricity passing through the wires. Even if you swing the compass the error will deviate according to device being running or turned off. To have a healthy angle after swinging the compass the plotter should always be running.

 

[Gladrags1]

A lot of interference from chart plotters is caused by the magnetic door for the sd card. Usually this is located on one end of the plotter. If you install the plotter keeping the door 11" away from the compass you should have less deviation.

Tod


Sent from my iPhone using Tapatalk

 

[hellosailor]

RTFM.

Does the manufacturer say anything like "DO NOT INSTALL WITHIN 36" OF ANY COMPASS" or something like that?

Some electronics emit magnetic fields, and they're not always consistent.

 

[capta]

Though we have a compass under our plotter at the helm, we rarely use it when the plotter is working; the plotter should give you a pretty accurate course, if you need one. We find ourselves either sailing on landmarks or towards a way point, using the chartplotter.
If the chartplotter failed and you needed the compass, perhaps it would be best to just remove the chartplotter when you need the compass, and not adjust it for the plotter, especially if the deviation changed depending if the plotter was on or off.

 

[jerryrlitton]

Deviation is the result of electricity passing through the wires. Even if you swing the compass the error will deviate according to device being running or turned off. To have a healthy angle after swinging the compass the plotter should always be running.

Any ferrous metal close to a compass can cause some deviation. You don't have to have electricity.

 

[MarkofSeaLife]

Whats causing the swing? It is probably the DC input. Maybe use twisted dc input wires.

I think Froggy gets the teapot or whatever the prize is. That a simple no cost trick to try that may do the, ummmm, well, trick.

If that doesnt work then I agree with CaptA: who the hell uses a compass??

 

[jerryrlitton]

If that doesnt work then I agree with CaptA: who the hell uses a compass??

How about when the chart gives bearings from two or more known points to fix a hazard in the water? You had best have an accurate or swung compass to fix that hazard? That's a problem when people put too much faith in the electronic God. We have them in aviation too.

 

[Capt Len]

Sometimes it's good to look at the bigger picture. Took a boat to San Diego once (before GPS or plotters). Compass would swing 30/40 degrees when the engine started and slowly come back as batteries charged. Turned out the output wire bypassed any switches and went up to dash ammeter and to both + terminals. Another vessels auto pilot would go screwy as more oSr less cans of food were stored in the same locker .In my own case , I have to be careful where I stick my sword when helming.

 

[ReefMagnet]

How about when the chart gives bearings from two or more known points to fix a hazard in the water? You had best have an accurate or swung compass to fix that hazard? That's a problem when people put too much faith in the electronic God. We have them in aviation too.

The thing here is that the typical recreational mariner would tend to use a hand bearing compass for this purpose of which compasses of this type normally don't have deviation calculated or factored into bearings read. I've only used my fixed compass for steering ever since GPS become standard equipment so the accuracy of the reading isn't important. If, OTH, I had the problem that the OP has and wanted an accurate reading I'd consider simply creating two deviation cards for the compass; one for plotter off and the other for plotter on (assuming some of the other excellent suggestions offered don't work).

 

[jerryrlitton]

Maybe a third card, to be used when wearing the sword.