Compass location and electronic equipment...

[Reel Knotty]

Hello All,

I am in the middle of a boat-wide rewire project (tired of the spaghetti wiring) and am re-locating some electronic gear in hopes of placing a new Ritchie compass on my dash without interference from the electronic gear. I have a '97 18' Alumaweld intruder, which means very limited dash space (if I am using improper term, please let me know...don't want to sound like a nimrod :blush: ). I am going to move the VHF under the dash. Both the GPS chartplotter and DS/FF are on the dash, the CB is also below the dash. Any suggestions? I know VHF and CB will probably be the biggest problem with the compass. Any of you guys found a good way to keep everything right in front of you without compass interference?

[Bluefinn]

It is a trial and error type of thing.before you mount your compass place it in a few different locations and see how much devaition you get do not forget to start your engine. As long as you know what the devation is you can always figure it in when you are correcting from true to magnetic or vice a versa.A general rule is to mount it as far away as possible.Magnets on speakers from radio are the worst.Rick

[USCGBoating]

Good advice. Also consider that the microphones will seriously effect the compass. As far as wiring, you can purchase shielded wires that will reduce the electrical infuence. Also there are electronic compases that have a remote sensor. These work great for areas where you have very limited space with a lot of electrical infuence. The sensor can be mounted up to 12 feet or more from the display.

[Gundog]

I am going through the same thing trying to plan where to put all of the electronics. If you have not bought your compass yet make sure you get one that can be adjusted for the deviation. You will not be able to adjust out all of the deviation so you will need to create a deviation table for it. This is something that I have learned from the ACN class I am taking. One option that I am considering is getting a compass that I can mount above eye level on the winshield frame. This takes a forward reading compass they are the same cost as the others they are just a different style they are used a lot for aircraft for the same reason to get away from the electronics. The only draw back to these type of compass is that it makes your compass read differently. What I am trying to say is if you were on a compass heading of 000 and you wanted to turn to 030 a standard forward reading compass would show 030 to the right or starboard of your current compass heading. The forward reading compass would show 030 to the left or port side initially this may make you turn in the wrong direction until you see your error. I am not sure I have explained this very well. :cheers:
Mike

[KeyWest]

Being cynical a bit here - but I notice the directions on all my electronics say to mount them about 30 feet away from the compass. On a 22' boat - kinda hard to do!!!

:laugh:

[Reel Knotty]

Yeah, noticed something similar in the directions I have...in an 18' boat it is just as hard :smash:

Looked into an electronic compass with a remote sensor, but a bit more money that I want to spend...

[Catching Nemo]

Here is a pic of what my limited dash space looks like. I used a Ritchie with the adjustment for deviation. It reads fairly close to what my 188 reads. Then again the 188 might be messed up also :jester:.

The most I have been offshore, or will ever be in my current boat, is about 12 miles. For that distance, it should get me pointed in the right direction and not driving towards Alaska despite whatever deviation still remains.

http://www.ifish.net/gallery/data/500/medium/4055100_0122.JPG

[Catching Nemo]

Just another thought? If you adjust for deviation with your equipment on, then what happens to that deviation when the power goes out. I imagine the magnet, in the radio speaker, will still have some effect.... :shrug:

For a 3 degree variation. How many feet is that at 10 miles?

[KeyWest]

Good point - I hadn't thought of that. I haven't notice my compass move when I turn something on or off - but then I haven't really looked for it either. My electronics are in an overhead box (I have a center console - T-Top).

[NorthRiverRick]

For a 3 degree variation. How many feet is that at 10 miles?



I just happen to have that bearing error table in my ACN class manual...

1048 yards or 3144 ft.

[Reel Knotty]

Catching Nemo,

Nice layout on the dash! I just picked up one the the adjustable mounts you use yesterday during my trip to Boater's World, West Marine, and Fisherman's in Portland. It is so nice having all three so close together. I had never been to West Marine or Boater's World before, so really enjoyed myself (and spent too much $$ :hoboy: ).

Right now I am considering putting the VHF under the dash to help with compass deviation problems. Of course I only go about 12 - 16 miles out in my boat on really nice days, so mostly I need it as a backup to head East if the GPS/Chartplotter goes gunnybags.

[Gundog]

There are two things to keep in mind your GPS is giving a true heading and the compass is giving you a magnetic heading with an error for deviation. If your variation for the area you are in is say 15* East (it will be marked in the compass rose for the chart you are using or maybe marked at the port somewhere)and the heading you are on with your compass has say a 3* East deviation your compass should be reading a heading difference of 18* from GPS to compass if they are reading closer you probably have a great deal of deviation and I would not trust the compass reading. The numbers I plugged in are randome but very conservative. You really need a deviation table for your compass and you need to know the variation for the area you are in. Variation is the difference between magnetic north and true north. Deviation is the amount of error your compass has for any particular heading you are on to magnetic.
Mike

[Catching Nemo]

There are two things to keep in mind your GPS is giving a true heading and the compass is giving you a magnetic heading with an error for deviation. If your variation for the area you are in is say 15* East (it will be marked in the compass rose for the chart you are using or maybe marked at the port somewhere)and the heading you are on with your compass has say a 3* East deviation your compass should be reading a heading difference of 18* from GPS to compass if they are reading closer you probably have a great deal of deviation and I would not trust the compass reading. The numbers I plugged in are randome but very conservative. You really need a deviation table for your compass and you need to know the variation for the area you are in. Variation is the difference between magnetic north and true north. Deviation is the amount of error your compass has for any particular heading you are on to magnetic.
Mike




Gundog,

Wow and ouch! Ok, so where can I take this ACN course (where and how much)? Sounds like a lot of good info.

The compass is really my tertiary backup because I have a hand held GPS as well but I need to make sure that I can still properly use it.

Thanks for that explanation.

[Bluefinn]

Very good Gundog you have been listening.

[Gundog]

Catching Nemo,
You are absolutely right I did not know any of this info before taking the ACN class.

I found out about the class on this board a while back. The class is taught by the Coast Guard Auxiliary. I am not sure when they will have another class we are in our 5th week (I think) of 13 weeks. Magoo was the one who set it up maybe they will have another one starting soon. I think it is worth taking.

The cost of the class was $60 which I think is really cheap the instructors are volunteers I think. The money is for your book and the class room use.
Mike

[Reel Knotty]

I would be very interested in the course as well. I am familiar with basic compass use (used to do back county back packing, and even some snow camping). However, a more comprehensive course on marine navigation would be great. My grandfather taught me quite a bit (he was Navy man, 40 years active and reserve...W4 for those of you Navy guys), but I was 12 years old at the time. He and my Grandmother took me on a 36' Grand Banks from Ketchikan Alaska to Newport Oregon one summer.

[BiteFactory]

In aircraft you have the same problem of small space, lots of metal and electronics. There is a mandatory little card attached near the compass that has the deviation at N,S,E and W. This is the deviation caused by the metal & electronics.

You'll see a compass painted on the ramp at airports. You take your plane out there, align with each point and see how much you are off. It is usually pretty small, like 3 degrees. Whenever things are changed it is good to re-do the deviation check.

[YaHoeeFishOn]

I was taught that all dc source wires imit a field. By twisting them around each other will negate the polarization . Check your true heading against chart running river sights on columbia.

[Reel Knotty]

All DC wires do emit a weak field, however, most of the power is under the dash, which means the aluminum (and paint to a miniscule degree) act as a shield. The wires that pass by the compass on the dash in my case are for the Fish Finder and GPS Chartplotter. Both of those units have shielded wires, so negate the field emmited. I have tested both the Fish finder and GPS Chartplotter next to the compass. Turning one at a time on, both at a time on do not cause any deviation of the compass. Next to test: VHF, CB, Windshield wipers, dash lights, Bilge pump (wires up front, should cause no problem). Cross my fingers since I like the new layout...

[Wright Angle]

When I installed my compass I checked for deviation with each electrical component on and off, one at a time. The only thing that seemed to make a difference is the wiper motor (3 or 4 degrees) it has a very large electrical magnetic field. Knowing this I set my compass up with the wiper motor off, as it will be off most of the time. If I ever need to totally rely on my compass (GPS Down) I know that I need to check my course with the wiper motor off from time to time. There is just not enough room on an 18' boat to mount the compass far enough from the electronics. W.A.

http://img.photobucket.com/albums/v718/WrightAngle/Dash2.jpg

[Mikeymoto]

How about a different type of compass, like a dash mount, window mount or a ram mount?
Just a random thought.
MM