prudenceb Posted August 13, 2010 Share Posted August 13, 2010 A friend and I were paddling for the first time together. Both of us have compasses on our boats. We found that the two were consistently giving readings 10 degrees apart. We checked to make sure neither of us had anything metal near our compass that might be affecting the reading. We didn't; the compasses stayed 10 degrees apart when both boats were totally empty. We didn't have a handheld to see which compass was reading correctly. Assuming that we figure that out, what to do with the compass reading inaccurately? Is it an installation problem (both were installed by experts)? A compass problem? How can we fix it? Any advice appreciated. prudence Quote Link to comment Share on other sites More sharing options...
subaruguru Posted August 13, 2010 Share Posted August 13, 2010 Hi Prudence, Are these both good quality Brunton, Silva, Ritchey (sp?), etc. compasses with resolution well within 10 degrees? If so I'd send it back for replacement. If it's a really cheap compass I wouldn't be surprised by the 10 degree (2.6%) error. Regardless, sounds like one of them has its "card" misaligned. I would suspect that the easiest way to "fix" it is to mark a new correct index line on the compass, and then remount it true to the corrected line. If the NEW index mark looks too similar to the old one you may get confused, so don't try to copy it exactly unless you make TWO new ones, wherein the MIDDLE one of the trio will be your guide. Indeed some compasses (like my new Brunton 85R) have three indeces. OTOH +/- 10 deg error is well within the noise in chop and combined human/compass resolution we're used to, so I'm not sure I'd worry too much about it. Indeed a bigger correction for magnetic declination (16 deg) exists too. Ern Quote Link to comment Share on other sites More sharing options...
Suz Posted August 13, 2010 Share Posted August 13, 2010 A friend and I were paddling for the first time together. Both of us have compasses on our boats. We found that the two were consistently giving readings 10 degrees apart. We checked to make sure neither of us had anything metal near our compass that might be affecting the reading. We didn't; the compasses stayed 10 degrees apart when both boats were totally empty. We didn't have a handheld to see which compass was reading correctly. Assuming that we figure that out, what to do with the compass reading inaccurately? Is it an installation problem (both were installed by experts)? A compass problem? How can we fix it? Any advice appreciated. prudence I have an installed P70 - Brunton or Silva or whomever it was made under - all the same compass. Mine was reading incorrectly on a recent trip and then I noticed that the landlubber lines were not actually lined up anymore. Just need to loosen the screws and realign and then tighten back up. If you were not the person installing it, then look here for the installation instructions. http://www.brunton.com/product.php?id=107 Suz Quote Link to comment Share on other sites More sharing options...
Brian Nystrom Posted August 13, 2010 Share Posted August 13, 2010 Are your compasses screwed securely to your boats? If you're using bungee or hatch cover mounted compasses, that's likely the problem as it can be difficult to align them accurately and consistently. Assuming that you have securely mounted compasses, have you adjusted the lubber lines on them? In case you're not familiar with that term, a lubber line is the line on the compass that indicates your heading. This needs to be adjusted so that it lines up with the centerline of your boat or it will not indicate your heading accurately, but it's something that most paddlers never think about. The instructions that came with your compass should tell you how to align it. Quote Link to comment Share on other sites More sharing options...
prudenceb Posted August 13, 2010 Author Share Posted August 13, 2010 Wow! Quick responses first thing the morning! Yes, both are good Brunton compasses, installled, not bungeed, in the boat. I'll take a look at the directions you link me to, and will look at those lubber lines and see if that's the issue. Thanks - prudence Quote Link to comment Share on other sites More sharing options...
kevinfre Posted August 13, 2010 Share Posted August 13, 2010 IMO, Ernie's last paragraph is the most likely answer - you don't have to move your bow very much to get a 10 degree difference. A 5 KT wind with a little chop can easily do it. When you and your friend were comparing headings were you lined up one behind the other, or side by side? If you were side by side, a 10 degree difference doesn't surprise me. I'm not saying you shouldn't check the other things people suggested - they're all good ideas from experienced paddlers. But if you can't pin down a hardware reason for this, don't be surprised. There might not be one. There's only so much accuracy you can expect in a human-powered craft. Kevin Quote Link to comment Share on other sites More sharing options...
prudenceb Posted August 13, 2010 Author Share Posted August 13, 2010 IMO, Ernie's last paragraph is the most likely answer - you don't have to move your bow very much to get a 10 degree difference. A 5 KT wind with a little chop can easily do it. When you and your friend were comparing headings were you lined up one behind the other, or side by side? If you were side by side, a 10 degree difference doesn't surprise me. I'm not saying you shouldn't check the other things people suggested - they're all good ideas from experienced paddlers. But if you can't pin down a hardware reason for this, don't be surprised. There might not be one. There's only so much accuracy you can expect in a human-powered craft. Kevin We tried it different ways - lined up, side by side, on land on sea - all 10 degrees difference. So I'll search for a hardware answer - or else do what we did - one of us always just subtracted 10 degrees and we ended up going the same way! Quote Link to comment Share on other sites More sharing options...
gyork Posted August 13, 2010 Share Posted August 13, 2010 We tried it different ways - lined up, side by side, on land on sea - all 10 degrees difference. So I'll search for a hardware answer - or else do what we did - one of us always just subtracted 10 degrees and we ended up going the same way! Seems you're still left not knowing if one or both compasses are out of synch. I would calibrate with a higher end, mirrored, hand-held compass for best accuracy, if you can find one. If you find that you're off by 5 degrees or less, I probably wouldn't tinker, and remember the deviation in your head. I'd recommend an adjustment for the bigger difference of 10 degrees, though, as a 10 degree error over a (seemingly interminable, like bushwacking) mile in Maine's pea soup may well leave you 1056 feet from your intended destination. Likely not a problem if you've fixed your "sights" for the center of an average-sized island, but if you're hoping to bump into can #9......... Gary Quote Link to comment Share on other sites More sharing options...
Pintail Posted August 13, 2010 Share Posted August 13, 2010 It sounds like an installation error to me. Pru, try to get a third compass from somewhere -- whether hand-held or on another kayak -- and use that one to tell you which to trust; <then> adjust the installation by moving the lubberline (white marker that coincides with your heading) of the apparently-erratic compass. While you are at it: check the lubberlines of both boats by holding a string from bow to stern and make sure of alignment. Declination should not be any problem -- and certainly not deviation, since we only paddle few miles at a time. I do not believe these compasses are adjustable internally: they are <fairly> elementary devices, that is. Good luck! Oh, last-minute thought: take both boats to Mr. Nystrom! He'll get yer right! Quote Link to comment Share on other sites More sharing options...
prudenceb Posted August 13, 2010 Author Share Posted August 13, 2010 It sounds like an installation error to me. Pru, try to get a third compass from somewhere -- whether hand-held or on another kayak -- and use that one to tell you which to trust; <then> adjust the installation by moving the lubberline (white marker that coincides with your heading) of the apparently-erratic compass. While you are at it: check the lubberlines of both boats by holding a string from bow to stern and make sure of alignment. Declination should not be any problem -- and certainly not deviation, since we only paddle few miles at a time. I do not believe these compasses are adjustable internally: they are <fairly> elementary devices, that is. Good luck! Oh, last-minute thought: take both boats to Mr. Nystrom! He'll get yer right! Thanks - if it comes to that, how do I get both boats to Mr. Nystrom? Mr. Nystrom, how do I find you?! (other than in your response above, that is) - prudence Quote Link to comment Share on other sites More sharing options...
jdkilroy Posted August 13, 2010 Share Posted August 13, 2010 To properly evaluate the compass independent of any other you will want to take a coastal (or better yet, a harbor) chart and establish as accurately as you can, a bearing to some prominent object in the distance that is both on the chart and visible to you. (a range or transit is best if you can set that up) Establish what the correct bearing from the chart is and correct it to a magnetic bearing (15 degrees W variation around these parts is close enough). Then compare your compass reading to what the chart says it should be. Be sure the boat is empty and no electronic/metal etc objects nearby. This is a lot easier to do than it sounds. best of luck, Jon Quote Link to comment Share on other sites More sharing options...
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