In our modern world we are isolated from weather even though we know more about weather than ever before in human history. We know, for instance, when a snowstorm is going to drop three feet of new snow in the mountain pass between here and Seattle; but we will drive to Seattle anyway and do it in a t-shirt and shorts. This remarkable disconnect between what we know and how we behave with that knowledge is something that paddlers have to battle with almost every time we sit our butts down in the cockpit. Fog and reduced visibility is a fact of life for many paddlers as the seasons moves inexorably into autumn and winter. The remarkable advances in clothing have, like your BMW, created a climate control for paddlers most of us old-timers are not used to. Today we can paddle comfortably in weather conditions that would have driven all but the craziest of us off the water ten years ago. Combine this with the simple fact that a lot of paddlers cannot follow a simple compass course and you could have a recipe for disaster. Airplane pilots receive some rudimentary - but mandatory - instructions in "instrument flying" and navigation while they are training for their pilot license. Kayakers, if they get any training at all, tend to concentrate on the technical details of paddling; rolls, braces, paddle strokes, etc. This is important - and fun - but I think it's also important for paddlers to learn how to deal with reduced visibility. The most basic "instrument" on a kayak is a compass. Unfortunately, most of these compasses are left in the accessory bag in the car and, if they are not, then they are a temporary ad-hoc addition to the deck. Often secured in place on a temporary basis with bungee cords with who-knows-what metallic objects stowed in a hatch right below. I would like to get one thing straight right off the bat. There are 360 degrees in a circle and your compass will likely divide them up into at least four 90-degree quadrants of N, E, S and W in addition to the numerical headings. I say this because you would be surprised at how many people do not know how many degrees there are in a circle or whether 090 refers to east (correct) or west (which is 270 degrees). The first step to understanding the instrumentation on your kayak is understanding that the "north" on your charts does not - unless you live in some very specific places - conform to the "north" shown on your compass. Hence the phrases "true north" and "magnetic north". This difference is caused by the simple fact that the magnetic pole - the chunk of whatever-it-is that attracts the needle of your compass - is not directly under the North Pole but is, instead, displaced some ways away from it. Too make matters worse, it's on the move. This is technically called "magnetic declination" but is most often referred to as "magnetic variation" and unless you live in an area of the world in which the magnetic north is directly in line with true north then you have to do an addition or subtraction of the difference before you can correlate the heading your compass is giving you with the geography presented on your navigational chart or map. The term "variation" also refers to some specific magnetic anomalies caused by changes in the earth's magnetic field in specific areas. These are often marked on navigational charts and have to be corrected only when your vessel is in that specific area. This link (http://www.ngdc.noaa.gov/seg/geomag/declination.shtml) is to the US NOAA web site explaining more than you need to know about this subject but also has a link to a map of variation and a calculator for determining your local variation. I encourage you to click on this link ( http://www.ngdc.noaa.gov/seg/geomag/icons/us_d_contour.jpg) and check the (2004) magnetic variation for your area. Where I live it was 18 deg east in 2004. Before we deal with the mechanics of converting magnetic north to true north (or vice-versa) we need to deal with another correction called "deviation". And, no, they won't put you in jail for this. The term "deviation" is used to describe errors in the compass itself and its close local environment not in the earth's magnetic field the compass is reacting to. Deviation includes correcting for metalic bits in the vessel itself as well as to built-in errors in the compass. Some compasses have adjustments for correcting for deviation (usually small movable magnets in the base of the compass) but most portable compasses have to be manually corrected. Compasses for small aircraft have a small placard which says, for instance, "FOR 090 STEER 096". Your kayak compass is unlikely to be usefull for heading differences of less than about 5 degrees simply because the compass card itself is of too small a diameter to inscribe the degrees and still be legible. In addition, just the movement of a vessel in a seaway will cause the compass card to swing wildly back and forth. In addition, changes in speed (acceleration and deceleration) and rapid changes in heading can create errors. Holding a compass course can often require that you mentally "average" the compass readings as you paddle along. If you have a GPS (and I strongly encourage every kayaker to have a GPS if only to keep track of your season paddling mileage) correcting for both variation and deviation is relatively easy. You simply set your GPS to show magnetic course and paddle a few yards in one direction while comparing the heading shown on the GPS with that indicated by the compass. The difference will be deviation (unless you are in an area of significant local variation differences). If you do not have a GPS then you have to do some classical marine navigation. One easy method is to drag your kayak to a place that is marked on a chart and, from there, use your compass to sight on another place that is marked on the chart. Use a plotter to determine the true heading between the two points and the difference between the compass reading and the plotted (true) heading is a combination of both variation and deviation. Variation will probably be shown on the chart's compass rose and there is also often an inner compass circle on the chart which you can use to plot the magnetic course (remember to compensate for the changes since the chart was printed). If not you can determine your local variation from that NOAA link (above. This new difference is entirely deviation so you can begin to prepare a compass correction card showing what courses to steer for a correct magnetic course with that compass and that load in your kayak. The insidious thing about deviation is that, unlike variation, it can change from one heading to another. It's quite common to have changes of greater than 10 degrees in a 90 degree course change. So to provide yourself with an accurate correction card for your particular compass you must, at the very least, do these procedures for at least 4 different headings about 90 degrees apart. What happens when you have a temporary mountable compass on your kayak? And what do you do when you add gear for a camping trip? And just how do you convert a magnetic course to a true course? That is left for part two. Tune in for more along with tips on using your GPS on long trips. Craig Jungers Royal City, WA *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Craig Jungers wrote: > In our modern world we are isolated from weather even though we know more > about weather than ever before in human history. We know, for instance, when > a snowstorm is going to drop three feet of new snow in the mountain pass > between here and Seattle; but we will drive to Seattle anyway and do it in a > t-shirt and shorts. This remarkable disconnect between what we know and how > we behave with that knowledge is something that paddlers have to battle with > almost every time we sit our butts down in the cockpit. [snip] Great piece, Craig. Keep it up. I have boxed the deck compass on my main hardshell once, which was 10 years ago [blush]. Time to do it again, even though I have never found any incorrect readings on it or any of the three other deck compasses I have boxed, over the years. In addition, the bearing my GPS gives, when underway under conditions that should give minimal drift, seems identical. We take each of our yaks to a local high point, set it on a mechanic's creeper and roll them around to three or four known landmarks to which we have established magnetic bearings (off a NOAA chart). As a double check, we do this at a couple different spots, and one or two sans creeper, to make sure there is nothing in the ground and no effect from the metals in the creeper to invalidate the boxing. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Nice text! Indeed I have too wondered about what people do when they encounter bad visibility - I do not carry a compass when on home turf (smaller than your lake) but both GPS and compass at sea, the latter especially helpful when your sailing your Klepper, as it is then easier to keep a straight course ;-)! Tord *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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