Set and drift

<h2 id="how-to-calculate">How to Calculate</h2>
<p>In order to utilize set and drift in <a href="/facts/Navigation/sGGAJ0AQ">navigation</a>, navigators must first set the course using Dead Reckoning.
</p><p>A <a href="/facts/Dead_reckoning/sljJ7nCT">Dead Reckoning</a>, DR, is calculated by using a previously determined position on a chart, and advancing that position based on known or estimated speed over a set amount of time. This can be calculated by using the formula Speed = Distance ÷ Time.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>Once an advance position has been plotted, then set and drift can be factored in. If there is a known set and drift, then the corrections can be applied to the Dead Reckoning position to then get an Estimated Position on a chart.
</p><p>The Course Made Good is the direction in which a ship or vessel has traveled with the effects of current, wind, and helmsmanship. If a current is flowing in the same direction as the ships heading, then the Course Made Good remains the same, but the current speed and ship speed are added together. If the speeds are in opposite directions, then the smaller speed is subtracted from the larger speed. If a vessel runs directly against a current or directly with a current, the speed of the vessel and speed of the current can be added or subtracted from each other. Such as, a vessel has a speed of 8 knots through the water and the vessel is traveling with the current, which is at 2 knots, then the speed over ground is 8+2 and the vessel's true speed is 10 knots.
</p><p>Set and Drift can be calculated by using a vector diagram and can be drawn and measured on a chart, <a href="/facts/Maneuvering_board/rtwGWg4e">maneuvering board</a> or even a plain piece of paper.
</p>
<h2 id="example-calculation">Example Calculation</h2>

<p>You are underway on course 150 degrees true at 8 knots. Your vessel is making good a course of 166 degrees true and a speed made good of 8.8 knots. What is your set and drift?
</p>
<ul><li>Step 1. Plot out course of 150 degrees true on Radar Plotting Sheet</li>
<li>Step 2. Measure length of course by using speed of 8 knots and converting into nautical miles via the time, speed, and distance scale</li>
<li>Step 3. Plot the length of speed on Radar Plotting sheet</li>
<li>Step 4. Plot out desired course of 166 degrees true on Radar Plotting Sheet</li>
<li>Step 5. Measure length of course by using speed of 8.8 knots and converting into nautical miles via the time, speed, and distance scale</li>
<li>Step 6. Connect the two ends of the vectors from the current course to the course made good. Thus creating your set and drift vector</li>
<li>Step 7. Using the navigational triangle, place on set and drift vector. Then drag to center crosshairs keeping the same angle and find the degrees on the outer circle</li>
<li>Step 8. Measure the length of the set and drift vector with the compass.  Convert from nautical miles into knots using the time, speed, and distance scale.</li>
<li>Step 9. Your set is 230 degrees true at a drift of 2.5 knots</li></ul>
<h2 id="tools-used-to-calculate">Tools used to calculate</h2>
<p>To use Navigation Triangles, a navigator need two of them to be able to navigate correctly. Navigation Triangles can be used to find <a href="/facts/Position_line/KVdYVLCc">Lines of Positions</a>, Dead Reckoning, <a href="/facts/Ranges-Navigation_Aids/IuogUza3">ranges</a>, Estimated Positions, Running Fixes and so on. They are also used to connect all the types of fixes to be able to determine a <a href="/facts/Course_(navigation)/CWexuXNF">course</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p><p>Dividers can be used for the measurement of lengths of lines on a chart and approximating the lengths of non-linear lines on a chart. Dividers can also be turned into a <a href="/facts/Compass-and-straightedge_construction/lbaHf2m7">compass</a> by replacing the metal leg of the divider with a piece of lead. A compass can measure and draw arc and circles on charts and maneuvering boards.
</p>
<h2 id="sources">Sources</h2>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Bowditch, Nathaniel (2002). The American Practical Navigator. Bethesda, Maryland: NATIONAL IMAGERY AND MAPPING AGENCY. p. 102. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Leviathan (21 May 2015). "What are My Electronics Telling Me About Boatspeed and Heading?". Sailing World. Retrieved 22 October 2017. <a href="https://www.sailingworld.com/what-are-my-electronics-telling-me-about-boatspeed-and-heading" target="_blank">https://www.sailingworld.com/what-are-my-electronics-telling-me-about-boatspeed-and-heading</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Deck License Prep. "Set & Drift and Leeway" (PDF). <a href="http://www.decklicenseprep.com/wp-content/uploads/2014/10/NS-140-Chapter-10-Set-Drift-and-Leeway.pdf" target="_blank">http://www.decklicenseprep.com/wp-content/uploads/2014/10/NS-140-Chapter-10-Set-Drift-and-Leeway.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Kessler, Gary (4 November 2016). "A Short Course on Nautical Charts and Basic Plotting For the Recreational Boater" (PDF). Version 3.4. Archived from the original (PDF) on 18 September 2017. <a href="https://web.archive.org/web/20170918024433/https://www.garykessler.net/scuba/library/Charts_Navigation.pdf" target="_blank">https://web.archive.org/web/20170918024433/https://www.garykessler.net/scuba/library/Charts_Navigation.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

Set and drift open-in-new

Set and drift