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    Re: Level of observation accuracy in medium seas
    From: Dave Weilacher
    Date: 2004 Jul 23, 08:13 -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{at}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{at}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{at}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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