NavList:

Just stepped out to the poop deck of my ketch here at Channel Islands Harbor to see what a set of four observations would give me using the calm surface of the harbor as an artificial horizon. What appeared to be calm wasn't. Looking through a 4X scope showed significant rippling of the Sun. A guess at the center was made on the reflected Sun image.

Intercepts 1.6'A, 8.3'A, 1.1'A, 1.3'A

Amazingly accurate considering the instability of the reflected image.

Greg Rudzinski

Re: An interesting question
From: Peter Monta
Date: 2013 Oct 11, 23:00 -0700
Lu Abel writes:

> moon directly aft of my stern. So I whipped out my sextant and used the
> waters as an AH. Reduced my sight and was disappointed to come out about 20
> miles from my KP.

That's interesting---was the image rippling at all? It's harder to
explain a 20-arcminute offset if the image was visually almost still
or rippling just a tiny bit.

That brings up the question: how good are "flat calm" liquid surfaces
from an image-stability point of view? They must range from shielded
AH on land (subarcminute at the very worst, maybe subarcsecond for all
I know, or at least diffraction-limited by the eye or scope, not the
AH aperture itself) to slightly ruffled seas in which the Sun or Moon
looks like a smear when averaged over many seconds. But even that
smear has some useful information. I wonder to what extent it would
average down if a navigator were forced to take many sights like this
in an emergency situation.

Cheers,
Peter
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