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    Re: Leg 46
    From: Dan Hogan
    Date: 1999 Feb 07, 21:37 EST

    Kevin, PMFBI:
    > Millard,
    >
    > Thanks for the reply. As to the proper spelling of the straight line
    > between two points - you're asking the wrong person! I can talk about
    > navigation, but when it comes to speellingg, thank God for spell checkers.
    > I do know about the spelling for the Rum line (the queue for drinks at the
    > bar).  :-)
    My route planning program uses Rumbline, probably to save space. My
    1973 Bowditch uses Rumb line.
    > I do have a question about your answer for sunrise in question seven.
    > Using the Celesticomp, I get your answer for 18 Feb in Sydney, not for 17
    > Feb. The Celesticomp calls for GMT times when using the sunrise program,
    > and when you are looking for sunrise in Australia on 17 Feb, it is still
    > 16 Feb in Greenwich. Are you sure of your time for question 7? Am I doing
    > it wrong here?
    Guys, this isn't rocket science. We are trying to stablish what would
    be a good early time to depart. Using a visual interpolation of the
    Nautical Almanac would be MORE than accurate enough. At sae your
    estimate of sunrise will depend on the accuracy of your DR. So plan to
    be ready at least 5 minutes before your estimate.
    
    [Snip Header]
    > Cc:	Kevin Redden
    > Subject:	RE: [Nml] Leg 46
    >
    > The answer of 70 days for problem #2 was arrived by the following method:
    > The rhumb line each leg was determined.
    >
    > Planning Routes--Port Jackson to Boston
    >
    > Port Jackson(Sydney) Departure--33d 50.8'S  151d 18.0'E
    > Tasman Sea Waypoint 1-----------34d 00.0'S  151d  40.0'E        20.5 nm
    > Tasman Sea Waypoint 2-----------38d 40.0'S  166d  45.0'E      783.5 nm
    > Destination N of Stephens Is.---40d 50.0'S  174d 00.0'E          360.0 nm
    > Wellington Departure Point------41d 30.0'E  175d 20.0'E            72.4 nm
    > Cape Horn-----------------------56d 04.0'S   67d 15.0'             4692
    > nm WPort Stanley, Falkland Is.------51d 40.0'S   57d 40.0'W          430
    > nm Mid-Atlantic Waypoint-----------00d 00.0'N   23d 00.0'W      3576.6 nm
    > Barbados------------------------13d 10.0'N   59d 20.0'W          2314.2
    > nm Cape Cod------------------------42d 10.0'N   70d 00.0'W	        1827.9
    > nm Boston--------------------------42d 20.0'N   70d 46.0'W
    > 35.6 nm
    >
    > Total    14,112.2 nm
    >
    > 14,112.2 divided by average speed of 8.4 kts  yields 1680.0238 hours
    > that divided by 24 gave 70.000992 hours.
    The answer is going to vary depending on the formula used for
    calculating Rumb line distances. i.e., what ellipsoid  and formula it
    used.
    > This answer is based on sailing time only and I did the problem as I
    > thought it was presented.  This in my opinion would only be estimate of
    > distance and time for planning.  I would assume the longer legs one might
    > sail the great circle, but I did not read the problem in that context.  On
    > the other hand the sailing of each leg might be longer due to winds and
    > currents, and therefore the overall distance may even be longer. I would
    > assume one would stop at some of these way points.  I know if I sailed
    > approximately 4700 miles I would like to get off the boat for a moment for
    > a little rum or beer.   :-)
    In 26,000 some odd blue ater miles I NEVER SAILED a great circle route.
    Hardly managed a Rumb line one. You kind of wander around chasing the
    wind.
    [Snip "Rumnb line & Header]
    > To: owner-navigation{at}XXX.XXX
    > Cc: Millard Kirk
    > Subject: RE: [Nml] Leg 46
    >
    >
    > After seeing the Silicon Sea cruises for the past two years, I finally
    > decided to start working the problems. I'm planning on trying to do a
    > long, celestial-only cruise this year, and I need to brush up on my
    > practice.
    >
    > I was puzzled by Answer #2. The 70 days given would only be correct if you
    > sailed rumb line courses for the whole trip. The problem is that nobody in
    > their right mind would do this! The rumb line distance of 14,112.7 nm is
    > 586.9 nm longer then the Great Circle distance of 13,525.8 nm.
    It's planning. You need some idea of what the voyage entails and where
    you will be ( more-or-less) to plan for weather and provisions.
    > By sailing the legs (other then the departure/arrival legs) using Great
    > Circle courses, the time required is almost 3 days shorter (67.1 days). Of
    > course, nobody figured in the time spent on sampling the rum and sobering
    > up again during the obligatory stop in Barbados!    :-)
    >
    >  Why was 70 days given as the answer to #2?
    Dan Hogan WA6PBY
    dhhogan{at}XXX.XXX
    Catalina 27 "GACHA"
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