Learn to Sail with Capt. Dan

 

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Capt. Dan's Coastal Navigation Course: Set and Drift   Bugaboos Bowditch on Dead Reckoning Set & Drift Exercises S&D Answer Key     Bugaboos There's nothing that strikes more fear into the heart of a midshipman studying DR than   play some ominous music here   Set and Drift. And there's hardly anything that makes a salt feel greater than telling said Midshipman - son, it's easy as pie. Not Pi, mind you, we still haven't got that worked all the way out. Easy as eating pie, maybe. There are a lot of hard ways to solve this. more ominous music here   THE dreaded TRIGONOMETRY. But we won't. Sorry to disappoint the engineers in the crowd. We'll just draw a couple of lines representing the Set - direction of current and the Drift - speed. We'll draw our DR - our intended course and measure directly what Set and Drift will do. Two Situations ASA 105 deals with two situations. Situation 1 - You're not where you thought you should be You travel for awhile, get a fix and you're not exactly where you thought you should be. Why not? Current! it's the big BUGABOO and includes all the forces that would drive us off course, including Set and Drift (current), leeway, steering error and anything else that throws us off our DR track. It is not, as you have figured, very pure. But before GPS, it was pretty darned important. This anachronistic calculation is pretty much superfluous, but it's on the test. Fortunately it makes sense and is quite easy. Situation 2 - You know (or have calculated) the current It's still just a matter of drawing a current line, a course line and a boat speed line. From all of that you determine what your SOG is and what heading you have to steer to maintain a COG. We're going to do all of this in class, but a little head start on understanding the vectors involved might be helpful. To that end, click hereto download a Powerpoint Show. For some reason, when this is downloaded to a Mac, it thinks it's an Excel program. It isn't, but if that happens to you, simply boot up Powerpoint and use the FILE OPEN command to open the show. Please call me 805.70.7828 if it doesn't work. Or e-mail me. <   Return to Top