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    From: Doug Royer
    Date: 2003 Apr 23, 10:17 -0700

    All boats are created equal.It's just some boats are created more equal than
    others.Small vessels are subject to the same physical phenomenon as large
    vessels.What are the physics of the edge of a prop closest to the hull
    creating more turbulance and drag than the edge of the prop further away
    from the hull?I don't know.I don't think I need to know.I am aware of the
    phenomenon and can plan accordingly to counteract it and that is important.I
    can't discuss with you guys the physics of this stuff because I'm not versed
    in physics.If a mariner is not aware of a phenomenon how can he plan to
    overcome it?
    Take for instance the area of optimizeing a prop.How many recreational
    boaters are aware that an optimized prop for a vessel will give better
    power,maneouverability and reduced fuel consumption?If not aware of it how
    can one take advantage of it?
    I will give you an actual test question that was on my 2nd Officers exam."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."What is this you say?This is as an important phenomenon in
    navigation as getting an LOP from a Celestial object I say.If you are not
    aware of it how can you take advantage of it?Small vessels can use the same
    ideas if aware of them.The art of practical navigation encompasses all these
    ideas not just one or two.
    The Merchant Marine is run on 2 basic principals,optimazation and money.With
    optimazation comes reduced transit costs and greater profit margins.Small
    vessels can use the same principals if aware of them.Optimazation of a track
    will take advantage of weather,current,wave and wind action and use it to
    ease or speed the advance.The same is done for avoiding areas that will have
    an adverse effect on the advance.Speeding up or retarding a leg of the
    transit to take advantage of calculated conditions further along the track
    is also a usefull proceedure.A case in point is both San Deigo Bay and the
    Bay of Fundy.San Deigo has an extremely narrow channel that is subject to
    high tidal currents.The Bay of Fundy has extreme swings in tidal
    heights,sometimes 20 ft. or more.You definetly don't want to be transiting
    these areas in any vessel at the extremes of the conditions.By being aware
    of the phenomena you can plan accordingly.You don't need to know the physics
    of the phenomena.
    So,getting as much info or knowlege as possible and being aware of it and
    then putting it to use in practical boat handleing or navigation is the
    essance of what this is all about.
    I'm so glad these subjects are comeing up on this board to discuss and learn
    as I think they are every bit as important as the fine points of Lunar
    Observations etc.
    I would like to ask a question of the group and in no way is it a
    criticism.I've just been wondering about it since reading the threads of the
    last few years.How many of you have done a Lunar observation on a voyage and
    used it?Please,this is not a criticism.

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