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: New Moon, Perigee, and Solstice
    From: George Huxtable
    Date: 2003 Dec 22, 11:16 +0000

    Frank Reed made the interesting comment-
    
    >These tides bring to mind something I noticed in old editions of Bowditch. If
    >I am remembering correctly, Bowditch from c.1800 says that the Spring Tides
    >(tides with maximum range) occur about three days after New Moon and three days
    >after Full Moon. That's not accurate in New England where the difference is
    >less than a day, but it is fairly accurate in northwest Europe which has unique
    >resonances. Bowditch, of course, copied earlier works and carried over lore
    >regarding European tides. So when did they fix it? Is there a 19th century
    >edition of Bowditch that has better basic descriptions of tidal phenomena?
    
    Response from George-
    
    I agree with Frank that coastal resonances must play a significant part in
    this tidal lag, where in many parts of Europe the highest tides follow a
    couple of days after the time of maximum tide-generating force. But are
    those in Europe "unique resonances"? I doubt it. What about that resonance
    toward the head of the Bay of Fundy, which produces the biggest tide-range
    in the World? I would guess that the spring tides, at the head of the Bay
    of Fundy, might well lag behind new-moon and full-moon just as much as they
    do in parts of Europe. But I don't have tide-tables for that part of the
    world. Does anyone have data to confirm (or disprove) that guess?
    
    Many think about electricity as an analogy to hydraulic flow, in terms of
    currents and pressures. On the other hand, as I have been involved in
    electrical measurements for most of my life, I draw my analogies the other
    way round, and think of such tidal phenomena in terms of electrical tuned
    circuits, such as you get in a radio. A tuned circuit has a factor, always
    known as its "Q", which describes its sharpness of tuning, and also its
    ability to enhance a driving voltage that's right at the frequency it's
    tuned to. It also shows a time-lag in its response to changes in such a
    driving waveform, which as I recall is just Q radians (which would
    correspond to about Q/12 days for a normal semidiurnal tide). In more
    complex situations, when one tuned circuit (or tidal basin) transfers
    energy to another, their lags can add.
    
    This information may be particularly useless for many Nav-l listmembers,
    but may ring a bell with others familiar with electrical matters. Someone
    may be able to tell me if my memory of these things is still about right,
    after many years of retirement.
    
    George
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
    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