NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant accuracy with short distance to horizon
From: Yves Arrouye
Date: 2001 Jun 28, 11:27 PM
From: Yves Arrouye
Date: 2001 Jun 28, 11:27 PM
> I very much like your explanation why one should add the wave > hight to the > height of eye when observing from a wave top. Only for one 'but': > your line of sight is tangent to the horizon, so for all > practical purposes > (wavelength assumed small w.r.t. curvature of earth) the > horizon is formed by > wave crests. There's no way of seeing a trough at the horizon > because there is > a crest relatively close in front of it. So both observer and > horizon are > raised by approximately the same distance (say, the > significant wave height), > and the dip should be calculated for the elevation of the > observer above this > raised horizontal level. BTW this is what Bruce Bauer says in his Sextant Handbook. He also says that on the bridge of a large ship, you want to correct for that, as only your horizon seems raised by the waves. YA