David Burch Navigation Blog
Notes on marine navigation and weather
Tuesday, May 19, 2026
Lunar Distance by Calculator — The Letcher Method
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The lunar distance method is a way to find UTC by measuring the angular distance between the moon and an adjacent body (sun, star or planet)...
Thursday, April 23, 2026
Wind on the Water: A Sailor's Perspective
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For sailors, wind speed is given in knots, and the direction of the wind is the direction it comes from. A north wind is blowing from the no...
Thursday, April 16, 2026
New Tidal Current Resource for Swiftsure and R2AK Sailors
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The excellent (free for Mac and PC) navigation app qtVlm has just added a new optional feature that is free for testing until May 15, 2026...
Wednesday, March 4, 2026
Grib Offsets for Routing in qtVlm
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When we compute the optimum sailing route in a nav app like qtVlm, we use the polar diagram of the boat to provide its performance expectati...
Saturday, January 10, 2026
Access Historic OSCAR Currents in GRIB Format
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May 5, 2026 Note : the near real time data set is being worked on at the moment, so the link below does not work past 3/17/26, but the Inte...
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