NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip uncertainty
From: Bruce Stark
Date: 2004 Dec 6, 15:08 EST
From: Bruce Stark
Date: 2004 Dec 6, 15:08 EST
I've dug up a couple of things that tend to confirm what Trevor and I believe.
From the chapter on Taking Observations in Raper's Practice of Navigation: "If the altitude be observed above the deck, as in the top for instance, the horizon will appear better defined, and the variations of the dip by the ship's motion will be less sensible: also the difference of temperature of the sea and the air appears to affect the place of the visible horizon less as the observer is more elevated. Hence it would appear that altitudes should be taken from aloft when convenient.
And from a 1943 edition of Bowditch: "Various methods have been suggested for computing the amount of dip for different relative values of temperature of air and water, but none of these afford a satisfactory solution." And further down the page: "The error will decrease with the height of the observer's eye; hence it is expedient, especially when error is suspected, to make the observation from the most elevated position available."
But I'd still like to see data from actual experiments.
Bruce
From the chapter on Taking Observations in Raper's Practice of Navigation: "If the altitude be observed above the deck, as in the top for instance, the horizon will appear better defined, and the variations of the dip by the ship's motion will be less sensible: also the difference of temperature of the sea and the air appears to affect the place of the visible horizon less as the observer is more elevated. Hence it would appear that altitudes should be taken from aloft when convenient.
And from a 1943 edition of Bowditch: "Various methods have been suggested for computing the amount of dip for different relative values of temperature of air and water, but none of these afford a satisfactory solution." And further down the page: "The error will decrease with the height of the observer's eye; hence it is expedient, especially when error is suspected, to make the observation from the most elevated position available."
But I'd still like to see data from actual experiments.
Bruce
