If I am planning a trip that spans two charts of the same scale that are side by side (i.e. the right side of one chart is the left side of the other), how does one determine a course to plot if the starting mark is on one chart and the destination mark is on the other?
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Charts overlap
You should be able to find either a landmark or a coordinate that is on both charts.
You should be able to find either a landmark or a coordinate that is on both charts.
Course Work
Anthony, As Phil said, pick a common point on both charts and at least temporarily fasten both charts together. Tape works best. I would not pick a landmark but but would use even geographical coordinates. i.e. intersection of a lat line and meridian line. Plot your two points and draw your course line. Measure the course using a central meridian between the points. If the central point is the joined portion between the two charts measure the course off of each chart using the best fit meridian on each chart closest to the joint. Average the two measured courses to get the average course. If you use this method go back and replot your average course using each meridian you cross. You will find that you will generally deviate away from your plotted course line for the first half of the voyage between the two points and converge back to the point during the second half. Be careful that your actual track doesn't place you somewhere you don't want to be. Happy ploting. ps You could also use the lazy method and enter both points into your GPS and have it determine the average course. Les s/v Mutual Fun
Anthony, As Phil said, pick a common point on both charts and at least temporarily fasten both charts together. Tape works best. I would not pick a landmark but but would use even geographical coordinates. i.e. intersection of a lat line and meridian line. Plot your two points and draw your course line. Measure the course using a central meridian between the points. If the central point is the joined portion between the two charts measure the course off of each chart using the best fit meridian on each chart closest to the joint. Average the two measured courses to get the average course. If you use this method go back and replot your average course using each meridian you cross. You will find that you will generally deviate away from your plotted course line for the first half of the voyage between the two points and converge back to the point during the second half. Be careful that your actual track doesn't place you somewhere you don't want to be. Happy ploting. ps You could also use the lazy method and enter both points into your GPS and have it determine the average course. Les s/v Mutual Fun
Angle and One Point Determine a Line
Plot to the last meridian on one chart, and walk the line over to the compass rose. On the other chart, pick up the meridian crossing, and walk the angle from the compass rose up to the start point, and extend the line.
Plot to the last meridian on one chart, and walk the line over to the compass rose. On the other chart, pick up the meridian crossing, and walk the angle from the compass rose up to the start point, and extend the line.
no silver bullet?
Thank you all so much for your posts. The only real good solution I have found so far is to simply butt the charts up next to each other and place the ruler so that it intersect your departure point with your destination, plot the course and then get the compass heading. Regarding the post 'Angle and One Point Determine a Line' Gene writes 'Plot to the last meridian on one chart'. But that is the problem. You don't know yet what compass heading to plot. That is what you are trying to figure out. With this method you would have to iterate. Guess one compass heading plot it to the end of one chart the then pickup the plot on the other chart and hope that the plot goes through your destination. If it doesn't then you have to guess again and start over. That doesn't seem like a good solution to me. I guess I figure that so many people have this same problem that there is some kind of silver bullet that I am missing?
Thank you all so much for your posts. The only real good solution I have found so far is to simply butt the charts up next to each other and place the ruler so that it intersect your departure point with your destination, plot the course and then get the compass heading. Regarding the post 'Angle and One Point Determine a Line' Gene writes 'Plot to the last meridian on one chart'. But that is the problem. You don't know yet what compass heading to plot. That is what you are trying to figure out. With this method you would have to iterate. Guess one compass heading plot it to the end of one chart the then pickup the plot on the other chart and hope that the plot goes through your destination. If it doesn't then you have to guess again and start over. That doesn't seem like a good solution to me. I guess I figure that so many people have this same problem that there is some kind of silver bullet that I am missing?
Tape 'em together
Anthony, Tape the charts together, find a surface large enough to allow you to spread out the whole works, get a straight edge (yard stick if necessary), draw the course and check it against the nearest rose. You're not going to off by much if any. You're not the first to span more than one chart.
Anthony, Tape the charts together, find a surface large enough to allow you to spread out the whole works, get a straight edge (yard stick if necessary), draw the course and check it against the nearest rose. You're not going to off by much if any. You're not the first to span more than one chart.
Use Rubber Cement
I'm an old Air Force navigator, and we always used plain rubber cement from the stationary store to stick charts together across areas, it is waterproof, you can rub it off with your thumb without hurting the map usually, and it will come apart if you are careful without ruining the charts.. Try it, I think you'll like it..though I would test the chart for color fastness in a small area first..good quality charts don't usually bleed when the cement contacts them.
I'm an old Air Force navigator, and we always used plain rubber cement from the stationary store to stick charts together across areas, it is waterproof, you can rub it off with your thumb without hurting the map usually, and it will come apart if you are careful without ruining the charts.. Try it, I think you'll like it..though I would test the chart for color fastness in a small area first..good quality charts don't usually bleed when the cement contacts them.
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