{"id":1729,"date":"2018-07-29T19:06:55","date_gmt":"2018-07-30T02:06:55","guid":{"rendered":"http:\/\/tradewindssailing.com\/wordpress\/?p=1729"},"modified":"2018-07-29T19:06:55","modified_gmt":"2018-07-30T02:06:55","slug":"coast-piloting-part-i-dead-reckoning","status":"publish","type":"post","link":"https:\/\/www.tradewindssailing.com\/wordpress\/general\/coast-piloting-part-i-dead-reckoning\/","title":{"rendered":"Coast Piloting Part I – Dead Reckoning"},"content":{"rendered":"

I’m not a fan of the term Coastal Navigation. \u00a0It has become quite popular over the past several years, however, it’s a bit too vague\u00a0to properly describe the process of safely operating a vessel in coastal waters. \u00a0The proper term, used for at least two centuries, is Coast Piloting. \u00a0Piloting is navigation which involves determining the position of a vessel relative to geographical\/terrestrial reference points. \u00a0With coast piloting, the reference points can be visually seen and then identified or matched to a reference on a chart of the area. To be able to identify that point on a chart requires you to have a pretty good idea of where you are to start with.<\/p>\n

As an example, a chart of Drakes Bay in Northern California looks very much like San Quintin Bay in Mexico, over 600 miles to the southeast. \u00a0Not having a general idea of where you are will result in some major errors in navigation. \u00a015 miles south of Drakes Bay, 5 miles offshore, is safe water nearing the approach to The Golden Gate. \u00a015 miles south of San Quintin, 5 miles offshore, is the Sacramento Reef, one of the most dangerous reefs on the pacific coast. \u00a0Not a good mistake to make. \u00a0The answer to having a good idea of where you are is Dead Reckoning (aka DR, Deduced Reckoning, or Ded Reckoning,) which is the primary topic of this tip.<\/p>\n

Dead Reckoning is determining the position of a vessel by applying the ship’s course and speed to the last known accurate position (fix.) An ongoing plot of course, speed, time, and distance is marked on a chart, resulting in an approximate vessel position. A DR position is an approximate position, not allowing for the effects of tide, current, wind, helms person error or compass error. \u00a0Whenever possible, the DR position must be updated to a more accurate fix, using bearings to visible objects and other lines of position that might be available.<\/p>\n

A DR plot requires a known starting point, and is referred to as “taking departure<\/strong>.” \u00a0This would be your last known accurate position fix, and is marked on the chart with a \u2297\u00a0as well as the time (noted horizontally on the chart). \u00a0The size of the circle represents the degree of accuracy of the fix. \u00a0This, and subsequent “expansion circles” around later DR positions indicate all possible positions of the vessel, and will be discussed further below.<\/p>\n

Items to be included in the plot are:<\/p>\n