C302 Compass Deviation Table
- Thread starter Interlude
- Start date
- Status
knotflying
Well-known member
- Joined
- Jul 25, 2010
- Messages
- 6,024
- Fluid Motion Model
- C-28
- Hull Identification Number
- FMLT2731J011
- Non-Fluid Motion Model
- 25' Parker & 246 Robalo Cayman
- Vessel Name
- http://illusionsmikeandjess.blogspot.com
Every compass is different. You have to determine that on your own. The best way is to have it on the trailer and using a hand held compass on the ground mark north, south, east and west. Then rotate the boat accordingly and note the differences. That will give you your deviation. Then you can make up a card to display that. Then you have to deal with Variation, which is the difference between what your compass is reading magnetic and true north. This changes by location. Where I live it is a 15 degree difference. When all is said and done, if using your chartplotter, none of these items are important. The GPS will guide you from point A to point B. Deviation and Variation were much more critical before GPS. However it is always good to navigate by compass and sextant to keep your skills sharp.
- Joined
- Aug 19, 2014
- Messages
- 514
- Fluid Motion Model
- C-24 C
- Non-Fluid Motion Model
- Cal 2-25
- Vessel Name
- S/V Saylee
- MMSI Number
- 338124769
Hi interlude,
Knotflying is right. You will need to determine your deviation from charts of your local area and adjust the compass accordingly. Also, keep in mind that it is good to have compass backup to the chart plotter in case a stray electron wipes it out.
Cheers,
Ralf
Knotflying is right. You will need to determine your deviation from charts of your local area and adjust the compass accordingly. Also, keep in mind that it is good to have compass backup to the chart plotter in case a stray electron wipes it out.
Cheers,
Ralf
bluestreak
Well-known member
- Joined
- Jun 25, 2010
- Messages
- 232
- Fluid Motion Model
- C-28
- Hull Identification Number
- fmlt2733c616
- Vessel Name
- Blue (2016) Call sign WDL3080
- MMSI Number
- 367752840
How you load your boat with various metalic items from one cruise to the next cruise, if not in the same location will affect the deviation.
CaspersCruiser
Well-known member
- Joined
- May 11, 2016
- Messages
- 869
- Fluid Motion Model
- R-27 Classic
- Hull Identification Number
- FMLT2709G112
- Vessel Name
- Cookie
- MMSI Number
- 368203460
Ralf, you’ve made a common error. From the charts of the local area, one determines magnetic variation (the difference between true north and magnetic north). In your neck of the woods, Seattle, magnetic variation is 16° east. That variation is the same for all boats.Ralf H":13nygkmd said:
Compass deviation is the error in the boat’s compass caused by magnetic influences on the boat in which the compass is installed. Those errors are specific to individual boats. The compass deviation on my R27 is different than the compass deviation on my friend’s R27. Compass deviation errors are typically less than 5°.
As Mike Rizzo (knotflying) says, if you’re using a chartplotter and GPS, magnetic variation and compass deviation are simply not a factor. When they ARE a factor is if you plot a course on a paper chart, which are oriented to true north, and you want to navigate along that course using the magnetic compass on your boat.
fishheadbarandgrill
Well-known member
- Joined
- Jul 15, 2018
- Messages
- 632
- Fluid Motion Model
- C-288 C
- Non-Fluid Motion Model
- Sunfish; Vespa GTS 300 Super
- Vessel Name
- Sea Shanty
- MMSI Number
- 368069690
Sounds like you guys need a good set of navigator's balls and then execute a turn ship evolution. That should work things out. 😀
knotflying
Well-known member
- Joined
- Jul 25, 2010
- Messages
- 6,024
- Fluid Motion Model
- C-28
- Hull Identification Number
- FMLT2731J011
- Non-Fluid Motion Model
- 25' Parker & 246 Robalo Cayman
- Vessel Name
- http://illusionsmikeandjess.blogspot.com
Always a good rule of thumb is to keep any metal or electrical components away from the compass. Those installed in the boat will never move and they are most likely the major sourse of the deviation. Put your iPhone up there and watch the compass turn while you aren't even moving.
Chimo
Well-known member
- Joined
- Oct 24, 2016
- Messages
- 714
- Fluid Motion Model
- C-26
- Vessel Name
- Chimo
- MMSI Number
- 316033437
knotflying":3uzcv2uy said:
I always thought about the phone but had a habit of dropping my keys on the dash. Interesting effect on the compass but nothing to what happened when I put my 12V air pump for the dinghy just inside the cave near the Garmin compass. That sent the apparent heading of the boat off by 60 deg.!
- Status