Windy Tops

Tag: compass

  • Detecting a faulty baseplate compass

    A Silva Field 7 Baseplate Compass
    My Silva Field 7 Baseplate Compass.

    Usually when intuition says one thing and a compass says something else, it means your intuition is wrong. More than a few times, I or a group I’ve been in have had a compass bearing telling us to go one way that intuitively seemed completely wrong, and after some time it’s turned out that we really were meant to push through an area that looked completely un-navigable. A couple of times, my sense of direction has become bizarrely flipped somehow inside my head, only to be corrected by a compass. On occasion, this has resulted in my sitting down in a flummoxed state for a few minutes trying to flip my head over, but it usually works out.

    One problem with a compass, though, is that the needle can occasionally flip—the south pole of the needle becomes north, and north becomes south, meaning the red end of the compass points south instead of north. This is exactly what happened to me on this occasion. The needle flipping actually happened some time before I left, and happened to be wrong when I first pulled it out to use it whilst inside visually encumbering cloud at 1400 metres elevation. Flipped needles are often a consequence of exposure to iron, in the same way that you can easily magnetise a pin by stroking it with a magnet a few times. In my case, I didn’t have a clue what’d caused it because my compass spends most of its time sitting on a shelf, but there are many things that might have caused it. Clearly this can be a problem, and if you’re trying to navigate it can also be a little risky if you’ve not realised what’s happening.

    There are a few ways to detect this in the field, though, and I’m keen to hear of any that I don’t mention here. Obviously if you know where you are and can see a known landmark, you can compare the compass to see if the needle’s pointing where you’d expect. If you have multiple compasses, you can compare them and at the very least determine if one compass is misbehaving. In my case, the first sign was that it tried to point me directly back the way I’d just come from, but in most such cases I’d still expect a compass to be more correct than my own intuition. Fortunately my GPS (usually packed away) includes an electronic magnetic compass, which I spent a few minutes calibrating, then compared the two.

    There’s yet another sign which might be common knowledge, but I can’t find any references on the ‘net so I thought I might share it. What should have been a dead giveaway for arousing suspicion in my case, especially in hindsight, was that the weighting of the needle within the compass was completely wrong.
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  • GPSs and Cognitive Mapping, or lack of it

    Late in 2010, I expressed some concerns about uses and perceptions of GPS receivers and similar technology. This article published in the New York Times (copied verbatim here if the NYT tries to force you to subscribe) refers to some of the concerns I share with risks relating GPS use. It’d be silly not to agree how fantastically useful it is to be able to pinpoint one’s position, especially in situations where safety demands it. On the other hand, it’s easy to get into habits of GPS use which don’t merely reduce one’s awareness in an immediate situation, but might also hinder those mental skills from being exercised or developing.

    A point made in the article is that the more traditional use of a map, which in a back-country context would sometimes be augmented by tools such as compasses and altimeters, requires a person to repeatedly refer to the surrounding physical world. It exercises parts of the brain responsible for generating cognitive maps of the surrounding area. Once a person begins to rely more on a GPS, these skills and abilities are lost, and spatial abilities degrade.
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  • GPSs, Compasses and Navigation

    Back in July, I wrote something about reports of a quick and painless helicopter rescue of a couple of people who’d become lost on Quoin Ridge, and especially how it was reported that they were in trouble due to a failure of their GPS. The point I was really trying to make was that the way it was reported, through propagation of a couple of simplified press releases that stated limited facts without analysis, implicitly validated reliance on a GPS as an acceptable way of avoiding getting lost, not to mention a cellphone as a rescue alert device, even though neither of these things is great to rely on. (I have no idea whether the reports accurately reflect what actually happened.)

    Reading about the incident, probably because of how it was reported, had me thinking more about why I don’t really trust GPSs in the outdoors. Actually, it’s not so much that I don’t trust a GPS as that I don’t think they naturally encourage a really good navigation sense as well as a map and compass can.

    I bought a GPS about a year ago, primarily for keeping track of where I’ve been. I usually just leave it switched on in the top of my pack, and it works very well. At the time, I expressed some concern that I might be less motivated to practice navigation skills. And yeah, I’ve used the GPS from time to time to get positions, but a year later I feel better about it, I think because I know I’ve also been improving my general navigation skills at the same time. It’s augmenting what I was already doing but not replacing it, and I’ve never felt as if I’m relying on a GPS and that I’ll be trapped or in deep trouble if it suddenly switched off.
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  • Media Impressions of a Tararua Rescue

    Sunday (a week ago, 11th July) saw what was probably a routine rescue mission in the southern Tararuas. A man (31) and a woman (27) from Wellington were somewhere in the vicinity of Alpha Hut and unexpectedly walking through deep snow. The Sun began to set, and their GPS batteries died. It seems they were lucky to be in a place where their phone worked, because they texted their last known position to friends to say they were scared for their safety, and were heading for Alpha Hut. The weather was very clear and calm, not expected to deteriorate any time soon. A helicopter crew spotted their torch light at about 6.30pm on Sunday night, using night vision goggles, and collected them.

    In some ways this rescue wasn’t very interesting. It barely made the news at all. It was reported very briefly in the DomPost, not even giving an approximate location, but reporting the GPS failure. A press release from the Life Flight Trust (duplicated here) adds a few more details, but wasn’t picked up and analysed by any popular media outlets that I can find. Also being a press release from the helicopter operator, its main focus is that they rescued people with their helicopter rather than explaining why those people needed rescuing.
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  • It’s only a magnet with a circle attached

    I bought myself a new compass yesterday, which was another Silva Field 7 baseplate compass, identical to the one that I lost last October. It’s the most basic Silva compass on the market. It’s often marketed as being “ideal for youth and beginners”. For me it seems to do the job perfectly well and while I’m not a navigation supremo, I’ve been working on it for a while now and I’ve not yet had any issues with having only the basic features. I guess they market it that way to drive people towards the more expensive parts of their range.

    For several months I’ve been using a baseplate Coleman compass that I found at Rebel Sport for a quarter of the price, and for me at least it works just as well as the Silva Field 7. It’s slightly larger though, if only because it includes extra features like a magnifier that I never use, and ultimately that’s why I decided to replace it. It’s only after I’d been using a smaller Field 7 compass for a while that I noticed the Coleman compass was actually quite heavy, and that’s why I bought myself another Field 7.

    It’s a shame they’re priced at about $35 for something so basic, which I think is more of a branding thing than anything else. If I could get a cheap un-branded compass of similar specifications then I would, but they’re hard to find on short notice. I suppose that all you really need is a magnetically sensitive needle inside a nicely divided circle. It probably helps some people to have a few features like a better grips on the dial thingee and a magnifier for maps (which I’ve personally never used), but I’ve yet to see anyone using something like a typically expensive sighting compass for tramping navigation in New Zealand. Perhaps it’s a consequence of the circles I associate with. They’re in the shops a lot so they must sell, and I’m quite interested to know what sorts of activities people use them for.

  • And now I need a new one

    That could have gone better. My compass has just been claimed by the Ruahine Range during an “unscheduled” pack-floating incident in the Oroua River near Iron Gates Hut. I think it must have floated out of my pocket while I was concentrating on other things which, to be perfectly honest, seemed more important at the time. In hindsight I still think they were, and my robust little navigational instrument was a necessary price to pay. I guess it says something for making sure that everything’s tied down. It’s probably most of the way out to sea by now.

    It was a Silva Field 7, which is a very basic baseplate compass and it does the job perfectly. They retail for about $30 so it’s no great financial loss. It’s still a bit of a downer, though, since I make an effort not to leave junk lying around in the wilderness.

    Other than that, it was a worth-while experience. I’ll write something and post photographs of the trip in coming days. Meanwhile you could read Robb’s account of his solo trip in the same area a few days beforehand.

    Update, 27-10-2008: It seems I wrote the account of the whole trip faster than I thought.

  • Expensive compasses

    I went shopping for a compass at lunch time today, as I can’t find my old one since arriving back. It turns out that not much has changed: the cheapest basic base-plate compass in a tramping shop is $30, and the ones worth getting are at least $45. Fortunately I managed to get a Coleman compass identical to my old one from Rebel Sport, which as far as I can tell is just as good, except it’s not a fancy Suunto or Silva branded compass with shiny lights and mirrors all over it.

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