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    Re: Waves and Dip
    From: Alexandre Eremenko
    Date: 2019 Dec 8, 13:43 +0000

    You are right: this "1/2 of the wave height" rule is not designed for small boats.
    It assumes that your height over water (when it is still) is much larger than the wave height.
    It cannot be applied to a small yacht when the waves are high.
    To see this, try to apply it to the extreme situation when a wave close to you 
    simply obscures the horizon.
    What you see then as your "horizon" is just the wave crest.
    Taking altitudes in these conditions is hardly possible at all, unless you 
    climb your mast (I remember reading in some 
    yachtsmen memoirs that this was actually done when an observation was badly needed).
    From: NavList@fer3.com [NavList@fer3.com] on behalf of Mike Freeman [NoReply_Freeman@fer3.com]
    Sent: Sunday, December 8, 2019 2:46 AM
    To: eremenko@math.purdue.edu
    Subject: [NavList] Waves and Dip
    "It is normal on the ocean to have a sea running, in the NE trades in mid 
    atlantic there will probably be a ground swell of 8 to 10 feet in height. In 
    the N Atlantic after heavy weather there could easily be a swell running to 
    20 feet or more. If this is the case youll have to estimate the wave height, 
    divide by 2 and add the result to your height of eye, youll only see the 
    horizon from the top of a wave so that is where youll be when you take your 
    I was surprised to read this.
    My imagination tells me when my small yacht is on a crest my horizon is also 
    made up of crests so no adjustments required?
    I also read some other special instructions for taking sights in large waves 
    which I am unable find but were different to either of the above.
    I guess different vessels vary?
    Look forward to replies
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