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David,
This is just an opinion because I don�t have any research to back it up with
and the few times that I have been in these conditions there was no way to
see how accurate the results of my sights were. When I was at the top of a
large wave (50 to 60 feet) it was possible to see a horizon that was the top
of a higher wave that was only 1 or two miles away. You cannot tell how far
or high the wave is that makes the false horizon because a white layer of
foam or spray covers the surface of the ocean. Some times it�s very hard to
tell what is the true horizon. But I have taken two sights in rapid
succession and found the sun was going backwards. No mater how bad the
weather gets I think it�s unlikely that the sun will try to run the other
way and hide. What does this tell you about the practice of navigation? Even
with lots of experience it�s not easy on the bad days and the corrections
for temperature pressure and dip don�t really mean much. You are just
getting an estimate of position.
All the best,
Robert Gainer


>From: David Weilacher 
>Reply-To: Navigation Mailing List 
>To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
>Subject: Re: Level of observation accuracy in medium seas
>Date: Fri, 23 Jul 2004 08:13:03 -0500
>
>Yep.  I exagerated wave height to make the point that it didn't matter how
>big the waves were at the horizon, I didn't think it would make a
>measurable distance to what your eye could see.
>
>In realistic terms, it is my intention to always be at home watching TV in
>those conditions.
>
>Keeping with the same exaggeration, I also can't see how, if my boat is at
>the top of a 50 ft wave and all I can see is the tops of 50 ft waves 8
>miles away, that will make any difference at all in my height of eye,
>compared to flat seas.
>
>Seems to me that what is happening is that we are adding 50 feet to the
>radius of the earth and that difference isn't measureable in any practical
>sense.
>
>
>-----Original Message-----
>From: Robert Gainer 
>Sent: Jul 23, 2004 7:44 AM
>To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
>Subject: Re: Level of observation accuracy in medium seas
>
>Dave
>A 50-foot wave by the Beaufort Scale means that you are in �exceptionally
>high waves. The air is filled with foam and the sea completely white with
>driving spray. Visibility greatly reduced�. The short description is
>�hurricane�. You might want to check out
>http://facs.scripps.edu/surf/luds.html, it has a very good and readable
>description of predicting wind speed and wave height. In practice you will
>not get a shot at anything because the wind and spray make it all but
>imposable to hold the sextant still. I have been in these conditions and
>speak from experience. By the way I think the height of a wave is measured
>from the trough to the crest.
>Robert Gainer
>
>
> >From: David Weilacher 
> >Reply-To: Navigation Mailing List 
> >To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
> >Subject: Re: Level of observation accuracy in medium seas
> >Date: Fri, 23 Jul 2004 06:42:03 -0500
> >
> >Hi Jarad;
> >
> >Can you point me to your source for Noaa wave height definition?
> >
> >Dave W
> >
> >
> >-----Original Message-----
> >From: Jared Sherman 
> >Sent: Jul 22, 2004 9:34 PM
> >To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
> >Subject: Re: Level of observation accuracy in medium seas
> >
> >Dave-
> >  <50 foot waves with a mile between peaks.  I take my shot when my boat
>is
> >at the top of a wave.  This is easy to tell because I can actually see a
> >horizon.  The horizon I see is 8 miles away.>
> >  Seems like short horizon. NOAA says that waves are measured from the
>sea
> >level, not from the trough to peak, so are you talking about real fifty
> >foot
> >waves, or "real" 50 foot waves, which most sailors would call hundred
> >footers?
> >
> >If the former, you're observing from 25' above sea level, figure ten more
> >for your deck and standing eye height, since you've got a good enough
>grip
> >to rider those doggies. That's 35' asf now, about your eight miles.
> >(7.9+)
> >
> >Nah, you're only in 25' waves, that's the problem. Wait for rougher
> >weather,
> >you'll get a better horizon.
> >
> >But you could certainly figure the math. A sphere (close enough)
>25,000
> >miles in circumference, two points 8 miles apart on that. Change the
>radius
> >of one by the 25' your far wave is blocking you...run some tangents and
> >angles..."A simple exercise left to the reader."
> >
> >Just remember, you're only in 25' waves.
> >
> >
> >Dave Weilacher
> >.US Coast Guard licensed captain
> >.    #889968
> >.ASA instructor evaluator and celestial
> >.    navigation instructor #990800
> >.IBM AS400 RPG contract programmer
>
>_________________________________________________________________
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>
>Dave Weilacher
>.US Coast Guard licensed captain
>.    #889968
>.ASA instructor evaluator and celestial
>.    navigation instructor #990800
>.IBM AS400 RPG contract programmer

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