Navigation and Seamanship (1+1)

Find out the distance between a shore object (whose height is known) and the vessel by using Vertical sextant angle

When measuring vertical sextant angle (VSA) of an object set the index at 0 and look at the top of the image down to coincide with the water line directly below it. For convenience in calculation ht of eye of the observer above the sea level. The distance between the vessel and the observed object could be calculated by using the following formula,

                                                      Height of the object in metre

Distance in nautical miles = ----------------------------------------------------------

                                                                 1852 x tan VSA

                                                      Height of the object in feet

Distance in nautical miles = ----------------------------------------------------------

                                                            6080 x tan VSA

               Or

                                                 1.855 (height of object in metres)

Distance in nautical miles = -----------------------------------------------------------

                                              VSA in minutes of arc

                                                     0.565 (height of object in feet)

Distance in nautical miles = -----------------------------------------------------------

                                                           VSA in minutes of arc