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    Re: awareness
    From: George Huxtable
    Date: 2003 Apr 23, 23:46 +0100

    Doug Royer asked-
    
    >How many of you have done a Lunar observation on a voyage and
    >used it?
    
    It's a fair question. Not me, for sure. Though I have my own small boat,
    I'm not an ocean-going passagemaker. No more than an armchair navigator,
    really. I doubt if I have the necessary sharp eye and steady hand, and
    coordination between the two, to manage a lunar distance at sea, even in
    calm conditions. Nor do I own a suitable sextant for that job. My plastic
    sextant is good enough for many purposes, but not for a lunar distance.
    
    In fact only two listmembers come to mind as having taken and used lunar
    distances on a passage; Steven Wepster and Arthur Pearson. If others have
    done so, they have kept very quiet about it.
    
    Doug asked (not sure exactly why)-
    
    >If the pitch of the prop is 26.3 ft. and the revolutions of the shaft is 87,421
    >revs. in a 24 hr. period,calculate the days advance allowing for a negative
    >7 % prop slip.
    
    Well, it's not a matter I have ever studied, but off the cuff (with a
    pocket calculator) I would guess the answer to be 351.7 miles. Doug might
    advise us whether counting the revs is really a valid and accurate way of
    calculating the distance travelled. It's not normally used on small
    vessels. Is the slip factor affected at all by strong head-winds, for
    example? Is the factor exactly the same at full power as it is when
    throttled back? Compared with towing a Walker log, which gives the more
    accurate answer?
    
    It might be only intermittently useful to the wind-sailors among us, but
    would it be valuable, to those that drive motor-boxes, to fit a
    turns-counter? Doug may know the answer.
    
    Finally, I wish to question Doug's statement-
    
    >The Bay of Fundy has extreme swings in tidal
    >heights,sometimes 20 ft. or more.
    
    At perigee springs, at the Northeast end of the Bay of Fundy, the tidal
    range can reach 50 ft, rather than the 20 ft quoted by Doug. Near here, in
    the Bristol Channel, it can exceed 40 ft. These are big tides.
    
    George Huxtable.
    
    
    
    ================================================================
    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.
    ================================================================
    
    
    

       
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