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Deck Hand
Posts: 11
Home Port: St James, NC
IP Logged | I have a 2007 Meridian 368 with a Danforth Compass on the bridge. I've checked the azimuth on the compass with the Northstar chartplotter and an additional Garmin GPS...both Northstar and GPS are synched, but the Danforth Compass is about 10 degrees off. I can't find any literature on how to "realign" the compass heading correctly. I did a forum search and didn't turn anything up.
Does anyone have .pdf file or instructions on how to go about resetting the compass to show correct azimuth? Thanks. |
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Admiral
Posts: 1235
Home Port: Jersey City, NJ
IP Logged | Are you sure the reading you got from your GPS is magnetic and not true? You also need to check for any metal around your compass that can throw it off.
There are adjusting magnets inside the compass and there is a procedure for doing it. It requires some skill though. Do you have a hand held compass? Take a bearing with that and compare it to your compass. |
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Admiral
Posts: 1235
Home Port: Jersey City, NJ
IP Logged | If you do need to adjust it, here are the instructions from Bowditch:
http://www.irbs.com/bowditch/pdf/chapt06.pdf
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Admiral
Posts: 416
Home Port: Longboat Key, FL
IP Logged | One of the first things I did when I got my boat was have the compass professionally adjusted to compensate for the magnetic variation in Florida versus Washington where it was built. It was only about 5 degrees off but enough that it bothered me in the event of a GPS failure in open water. I was amazed at the complexity of properly calibrating a compass. The guy I used set up a tripod with an orientation compass on the dock (no movement), made repeated long site lines to the horizon from the boat to the dock and the dock to the boat, took into account the surrounding magnetic influences (electrical wires, equipment, etc.), and rechecked it twice by spinning the compass with some large magnetics. My compass is always in sync with my GPS and chart plotter. |
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Deck Hand
Posts: 11
Home Port: St James, NC
IP Logged | Pete - thanks for the info. Think this is what I'll have to do...the directions to calibrate on your own in open water is really too hard to do, but the variation in the compass and my plotter/GPS is certainly distracting as you said it was for you as well. Was this a person from a Marine shop or from a Marine Instrument sales shop? Curious how to find such a guy here in Southport, NC.
Bill |
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Admiral
Posts: 1235
Home Port: Jersey City, NJ
IP Logged | For those who don't know, here is a little primer.
Variation is the difference between True and Magnetic. As Pete said, it is different wherever you are but the Variation is always indicated on a chart and it can increase or decrease as time goes by. That change is also indicated on the chart. You have to look at the date of the chart. The compass rose on the chart shows both True and Magnetic. The Magnetic North Pole is different from the real North Pole. That's what causes the variation.
Deviation is the difference between what Magnetic is and what the compass reads on your boat and is caused by metal on your boat around the compass that can throw it off. You can adjust for this using magnets that are built into the compass for this purpose. This can change if you install new electronics or other metal near the compass.
Your GPS can be set to display True or Magnetic. Generally, compasses are not adjusted to compensate for variation in a given area. You should set your GPS to read Magnetic and compare that reading to your compass. You can also look at the true reading on your GPS, look up the variation on your chart and compare that to your compass. The Variation in my area is around 14 Degrees West.
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Deck Hand
Posts: 44
IP Logged | Your ship's compass is a pretty important piece of gear. It is wise to ensure it is as accurate as possible. It is important to only use stainless steel, aluminum and brass (non ferrous metals & hardware), when installing additions near the compass and flux valve/gate. If you are installing electronic gear, thin nickel sheeting can be used to block the EMF from the compass or flux valve/gate.
Bill |
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Admiral
Posts: 416
Home Port: Longboat Key, FL
IP Logged | Bill - The guy I used was from a commercial marine navigation service out of Ft. Lauderdale. These are the same guys that do calibrations for commercial vessels and mega yachts. He was expensive (about $400) but did a fantastic job and I have had no issues since. I'd suggest you ask around the docks near your home port where there are commercial boats, tugs, etc. They will point you in the right direction (pun intended).  |
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Danforth Compass Alignment
