Discussion: Declination

I adventure race in Michigan. We are 5-6 degrees westerly for declination and I've been told I don't really need to worry about adjusting my compass for this small amount. Over a 1000m route between two CPs, wouldn't this make a difference? Thanks for your advice.

The easy way to adjust for declination is to draw magnetic north/south lines on your map before the race.

But the larger question would be the wisdom trying to follow a bearing for 1000m. This is probably too far for the obtaining the accuracy you would want, especially through those subtle Michigan woods.

Deviation over 1000m at 5° is ~87m, and at 6° is 105m, so I'm not sure why you wouldn't want to account for it. I think you've been given some bad advice.

Geoman - 1-1.5km is a pretty common length for blind compass legs on rogaines, and on the rogaine last weekend my team had accuracies of <20m across that distance. There's no reason ARs wouldn't expect similar accuracy from competitors, and of course any sensible person doing such a leg would aim off, find a better attack point or (as a last resort) hope like hell.

Most of our CPs are 240-700m but threw out the 1000m figure as I figured deviation might be significant at that distance. The reason the question came up is because I almost always find myself left of the CP and I wondered if it was a hand/eye bias or deviation. Thanks for your advice.

If you don't have time to draw north lines, just take your bearing and add 5 degrees, i.e. turn your compass to a number 5 degrees higher than what you read off the map. Most people are unable to follow a bearing super-accurately over a long distance but that will remove declination as one of the variables. As mentioned, you'll also want to look for other ways to locate your CP besides the bearing to avoid that unpleasant needle-in-a-haystack experience.

Depending on your compass and the way that you take your bearings, there are various ways to account for declination mechanically. You may have seen some backpacking compasses that have a tunable declination adjustment. You can obtain similar effects on your favorite compass with some carefully drawn sharpie marks or a well placed strip of tape.

There might be another reason why you find yourself left of the CP. When I train people and watch them when they follow a bearing, many people have either tendency to move right or move left when they encounter an obstacle like some dense vegetation or boulder. Once I have observed it several times during the practice and see a pattern, I point out that they need to move back to the line after each object or at least be aware of their tendency.
As it was mentioned before, we rarely run on a blank piece of paper, there are objects on the map which can be used for navigation. I must admit, I have seen so many AR maps with every bearing between CPs nicely marked before they started. I see disaster looming with this mechanical approach and tell them to read the map, use big features and rely on more than just a bearing.

Yup read the map so to do this best put magnetic north lines on your map (you only need to do this where the course will actually go) so you can both take bearings and most importantly orient the map!

I read something somewhere in some book - so it must be true ;) that most baseplate compasses are accurate to about 2 degrees and that a person would also generally walk a straight line at about a 2 degree error. So the error would be just under 3 degree by the root of the sum of the squares.

I once was on a course where the map had Magnetic north and true north switched. Where I'm at the declination is 8 degrees, so with this switch it made it 16. Funny thing, I didn't notice until a year after the event when I was looking through my maps.

So what does this all mean? I don't know (nothing else is going on tonight). In the end, I use either a declination corrected map, or declination corrected compass because it just makes me feel good. But really, I focus on map reading, and use the compass as an aid when needed (which at times is crucial).

I appreciate the words of wisdom. The challenge in Michigan woods is that attack points, handrails and other defined features are fairly scarce. I'm looking at my map from my last 15 hour race a few weeks ago and of 20 score-o CPs of 300-750m, I feel like over half of them needed a closely followed bearing. But based on the feedback, I realize I'm probably not trusting the map like I should. My fear is that if I miss something on the map, can't find the attack point, etc., then I have no bearing and may have to retreat back to the previous CP, wasting precious time. Instead, I follow the bearing at a fast walk and rarely get into trouble. It's hard to make that leap of faith in these woods.

It's been my experience in the woods of eastern Canada that 2 degrees accuracy is the best one can hope for while still maintaining any kind of race pace.

I'd say you definitely need to account for the declination.

Some people, especially in AR, don't worry much about declination since precision bearing bushwhacks aren't very common... but I think it's poor practice. You need bearings for more than just bushwhacking.