NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: CN & global ocean currents
From: Lu Abel
Date: 2019 Oct 30, 16:24 +0000
From: Lu Abel
Date: 2019 Oct 30, 16:24 +0000
Igor:
Pilot Charts, available for all the great oceans, show the average wind speeds and directions for each 5 x 5 degree L/Lo section of the ocean. They similarly show the average current for each block. Pilot charts are issued for each month of the year since these data typically change with the seasons.
A Dead Reckoning (DR) position is, by definition, derived from only a vessel's speed and course and does not take current or drift into account.
But an Estimate Position is a DR augmented by extra knowledge such as speed and direction of currents affecting the vessel and can therefore give a more accurate estimate of a vessel's position than just a DR.
In my humble opinion, too many offshore navigation courses give short shrift to taking currents into account and developing an EP as a more accurate estimate of a vessel's position.
Lu Abel
On Tuesday, October 29, 2019, 6:04:07 PM PDT, Igor S. <> wrote:
In our CN course I've heard the following interesting idea. Suppose that during the ocean crossing celestial fix systematically deviates from the dead reckoning (DR) position in more or less the same direction. The following conclusion can be drawn - the existence of a global ocean currents ( https://en.wikipedia.org/wiki/ Ocean_current ). The earlier navigators were the first who might have noticed that. I could not find a clear reference on this account. Perhaps someone knows more details about it.
kind regards,
Igor
