Reply
 
Thread Tools Search this Thread
 
Old 19 May 2011, 14:50   #1
dnv
Member
 
Country: Germany
Town: Hamburg
Boat name: Der Delphin
Make: Parker
Length: 6m +
Engine: Inboard Diesel 120HP
Join Date: Dec 2008
Posts: 168
compass compensation

Hi there


My Suunto (see attached picture) deviates from 5 to 12 degrees, depending on the true heading. The compass has little magnets underneath for compensation.

I found advice on howto compensate here and there:
Compass Compensation
Ritchie Navigation - Compass Compensation
http://www.google.de/url?sa=t&source...k_4vBQ&cad=rja

Does anybody on here have other, maybe more simple, advice?

thanks for any help in advance, Jan
Attached Thumbnails
Click image for larger version

Name:	photo.jpg
Views:	117
Size:	49.8 KB
ID:	59491  
__________________

__________________
dnv is offline   Reply With Quote
Old 19 May 2011, 16:58   #2
Member
 
Country: UK - England
Boat name: Sea Hornet
Make: Humber
Length: 5m +
Engine: O/B 90hp
Join Date: Apr 2010
Posts: 195
compass

[QUOTE=dnv;401737] Hi there


My Suunto (see attached picture) deviates from 5 to 12 degrees, depending on the true heading. The compass has little magnets underneath for compensation.

I found advice on howto compensate here and there:
Compass Compensation
Ritchie Navigation - Compass Compensation
http://www.google.de/url?sa=t&source...k_4vBQ&cad=rja

Does anybody on here have other, maybe more simple, advice?

thanks for any help in advance, Jan [/QUOTE


Compass deviation is the error introduced by external influences such as ferrous metal components, magnetic materials or electrical cables which are too close to the compass.

The proper procedure:

Once all such influences have been minimised the correct course of action is to check swing the compass. Using a calibrated hand bearing compass take readings from a position about 10 meters in front of the bow, looking down the centreline from the bow to the stern, with someone monitoring the boat compass. Take a reading on the boat compass on 0, 90, 180 and 270 degrees and write down the headings shown on the boat compass. Using the mini magnets, correct these errors remembering that that over correction will cause errors on the reciprocal. Correction with in 3 degrees should suffice.
Now do the same ever 45 degrees. Errors that can't be eliminated are entered on a "compass deviation card" fitted next to the compass. So, for example if there remains a +3 degree error on North, the deviation card will read heading 000 - steer 357 and so on. This card should start 000 and list headings every 45 degrees.

The quick procedure:
Minimise external influences. Using a GPS at slow speed in flat conditions, adjust your headings N,S,E,W and then check every 45 degrees. Remember GPS is true heading so allow for variation in your area. For any remaining small errors, if you wish, you can make up a deviation card as above.

Having said all that, if you can read your compass within 3 degrees at 30 kts in anything less than glass conditions, you're a better skipper than me.

Good luck

JW
__________________

__________________
Firefly is offline   Reply With Quote
Old 19 May 2011, 18:48   #3
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Quote:
.....you're a better skipper than me.

Good luck

JW
Oi !!! Who's this JW fella?
__________________
JW.
jwalker is offline   Reply With Quote
Old 19 May 2011, 22:00   #4
Member
 
Country: UK - England
Town: NW& wherever the boat is!
Boat name: depends on m'mood!
Make: Humbers/15-24m cats
Length: 6m +
Engine: etec130/big volvos
MMSI: many and various
Join Date: Nov 2001
Posts: 1,815
have a look at my post here some time back re adjusting
Compass fitting.
the screws only turn a couple of bar things that are securely attached to the screwend rod so its no use screwing them in thinking they will adjust more as you turn the rod more-they just rotate thru 360 degrees if that makes sense--its early morning and a tad lumpy out here at sea so fully coherent sentences are not forthcoming
__________________
Dave M
www.wavelengthtraining.co.uk
wavelength is offline   Reply With Quote
Old 19 May 2011, 22:04   #5
Member
 
Country: UK - England
Town: NW& wherever the boat is!
Boat name: depends on m'mood!
Make: Humbers/15-24m cats
Length: 6m +
Engine: etec130/big volvos
MMSI: many and various
Join Date: Nov 2001
Posts: 1,815
Quote:
Remember GPS is true heading so allow for variation in your area
or go into the gps menu and set it to magnetic instead of true, it will sort variation out by itself and may even occasionally agree with the compass
ho-hum 0300 hours
__________________
Dave M
www.wavelengthtraining.co.uk
wavelength is offline   Reply With Quote
Old 19 May 2011, 23:25   #6
Member
 
Country: UK - England
Boat name: Sea Hornet
Make: Humber
Length: 5m +
Engine: O/B 90hp
Join Date: Apr 2010
Posts: 195
true and mag

Quote:
Originally Posted by wavelength View Post
or go into the gps menu and set it to magnetic instead of true, it will sort variation out by itself and may even occasionally agree with the compass
ho-hum 0300 hours
Wasn't sure that was possible, that's even easier.
__________________
Firefly is offline   Reply With Quote
Old 20 May 2011, 00:51   #7
Member
 
Country: UK - England
Town: NW& wherever the boat is!
Boat name: depends on m'mood!
Make: Humbers/15-24m cats
Length: 6m +
Engine: etec130/big volvos
MMSI: many and various
Join Date: Nov 2001
Posts: 1,815
you must be on nights
We always run the gps on magnetic so as we are using the same bearings on compass and gps.
Daylight now and I can see its rough instead of just feeling that it is!
__________________
Dave M
www.wavelengthtraining.co.uk
wavelength is offline   Reply With Quote
Old 20 May 2011, 04:02   #8
Member
 
biffer's Avatar
 
Country: UK - England
Town: swanwick/hamble
Boat name: stormchaser
Make: custom rib
Length: 8m +
Engine: inboard/diesel
Join Date: Aug 2007
Posts: 3,848
i've never been able to get a magnetic compass to perform that well on a rib, there are too many things to influence it in such a small area, if you have cable steering it will affect your compass when there is a larger amount of steering cable in the console at full lock, bags in the console that weren't there when you swung it, keys on the dash, throttle controller in gear(nearer the compass), the list goes on, you get it as near as you can and it will all change next year when it will need correcting again, i hate to say this being old school but electronic's are the way forward and a compass on a rib should be used for general reference
__________________
biffer is offline   Reply With Quote
Old 20 May 2011, 04:18   #9
Member
 
Country: UK - England
Boat name: Sea Hornet
Make: Humber
Length: 5m +
Engine: O/B 90hp
Join Date: Apr 2010
Posts: 195
gps on mag

Quote:
Originally Posted by wavelength View Post
you must be on nights
We always run the gps on magnetic so as we are using the same bearings on compass and gps.
Daylight now and I can see its rough instead of just feeling that it is!

That makes sense. However in my case, (small rib with small compass), in anything other than a mill pond sea, I confess to relying on the GPS hdg and trk with the compass as back-up.

Are you still at sea?
__________________
Firefly is offline   Reply With Quote
Old 20 May 2011, 04:22   #10
Member
 
Country: UK - England
Boat name: Sea Hornet
Make: Humber
Length: 5m +
Engine: O/B 90hp
Join Date: Apr 2010
Posts: 195
Quote:
Originally Posted by biffer View Post
i've never been able to get a magnetic compass to perform that well on a rib, there are too many things to influence it in such a small area, if you have cable steering it will affect your compass when there is a larger amount of steering cable in the console at full lock, bags in the console that weren't there when you swung it, keys on the dash, throttle controller in gear(nearer the compass), the list goes on, you get it as near as you can and it will all change next year when it will need correcting again, i hate to say this being old school but electronic's are the way forward and a compass on a rib should be used for general reference
That, of course, is the reality. The theory makes interesting reading
__________________

__________________
Firefly is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 22:40.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.