Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Plastic sextants. was: GPS shortcomings.
    From: Bill B
    Date: 2005 Jun 13, 00:17 -0500

    > George H you wrote:
    > "Dave makes a fair point,  but as I see it, it would apply only to
    > observations where a significant  fraction of the length of the sight-path
    > to the horizon is over the land (or  sandy shore, or drying reefs,
    > whatever). Otherwise, the surface temperature,  even in shallow water, would
    > not differ all that much from the open sea,  except in some very-odd
    > environments."
    >
    > There's more to it than that.  You can get more complicated layering of air
    > layers with different temperatures  close to shore. Near Mystic, Connecticut
    > in
    > the spring and fall, it's not that  uncommon to see five or more arcminutes
    > of anomalous dip, and this is for sights  taken on water (but within sight of
    > land).
    
    This is something that has been bothering me since my experiences on Lake
    Michigan last weekend.  With approx. 65F water temperature, 85F air
    temperature, and a white strip apparently covering the sharp horizon, I
    would have expected my Ho's to be larger than my Hc's as the line I used
    between the water/white strip might have been lower than the actual horizon.
    I was surprised to find all my shot Ho's to be smaller than Hc's.  I would
    not discounting pilot error on my part of course.
    
    As a rule of thumb, what is the trend of,  "...it's not that  uncommon to
    see five or more arcminutes "of anomalous dip, and this is for sights  taken
    on water (but within sight of land)."  That is, how will it shift Ho vs. Hc?
    Is a trend semi-predictable trend for cold water/warm air and/or warm
    water/cold air?
    
    Thanks
    
    Bill
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site