Suunto D-135 Adjustment

sheethead

Member
362
2
Branford CT
I need to adjust my Suunto binnacle compass to compensate for declination. The boat is 25 years old and this has never been done, it's off by around 10*. Searching the Suunto site and asking my old friend Google, I'm coming up empty handed. There are what I assume are adjustment screws on the outside of the casing but I really don't want to start dicking around with it until I have a clue of what the process is.

Help a brother out?

Thanks!

 

casc27

Super Anarchist
2,352
133
What? Are you trying to adjust your compass such that it indicates true North rather than magnetic North?

The adjusting screws you see are there to allow compensation for deviation, which is the difference between magnetic North and what the compass is indicating. Declination (or variation), on the other hand, is the angle on the horizontal plane between true North and the direction the compass needle indicates (magnetic North).

Deviation is caused by local magnetic fields on the boat. These can be caused by other permanently installed equipment, portable items (put your steel anchor next to your compass and see what happens), electronics and wiring among other things. Have you owned the boat for the entire 25 years? How do you know that no adjustment was done during installation? If nothing major has changed (which is admittedly unlikely after 25 years) there is little reason to go mucking around with things. The current declination in CT is around 13 degrees West (negative). So, if your compass is reading off by about 10 degrees (at least in one direction as you did not mention swinging the compass or preparing a deviation table) you are not that far off.

If you really feel the need to mess about there is a good, basic description of things here: http://l-36.com/compass.php

 

sheethead

Member
362
2
Branford CT
Thanks for the info casc. No I am not trying to adjust so it indicates true but that notion makes me realize where this all started.

Obviously some of my vernacular and understanding is off, so I will edumacate myself with that link you posted. BRB

 

sheethead

Member
362
2
Branford CT
Stupid question time... Does a tacktick use a magnetic heading?

I started using a GPS last year and I think that is fucking with me. I guess I am reading true North and the compass is reading magnetic. That kinda makes sense.

 

Itsabimmerthing

Anarchist
770
11
Europe
GPS would give you COG course over ground, relative to true north.

Variation will always be there and changes sloooowly over time.

Deviation is constant as long as there is no magnetic changes in the boat. Adjusting "spikes" off a compass is not easy. Well adjusted compass has deviation sine curve like deviation.

Want true heading? Get a gyro.

 
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