Next message: David Weilacher: "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:
>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:
>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?<G>
>
>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.<G> 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.<G>
>
>But you could certainly figure the math. A sphere (close enough<G>) 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.<G>
>
>
>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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