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    Re: Long and Time at Sea
    From: John Kabel
    Date: 2005 Jun 6, 16:03 -0400

    Well, that means someone from CPS has to pipe up!
    Canadian Power and Sail Squadrons (originally Canadian Power Squadrons) is
    the independent northern version of USPS.  CPS started with three guys from
    Windsor, ON going over to Detroit to take their Boating Course.  And the
    rest is history.  And we CPS people certainly thank our USPS "parents" for
    their tolerance in the beginning.
    Jim Thompson is undergoing (or maybe has just passed) the rigors of CPS CN,
    and can shed light on the current situation.  When I did it, it was two
    courses, Junior Navigator and Navigator, taken in order.  You had to submit
    a unique sight folder for each, each checked locally, then by the Course
    Director.  JN error limit on the fix was 5 nm, N was 3 nm.  The successful
    grad of a CPS mainline course gets to use his grade after his name on
    correspondence.  Senior Navigators, those with a full certificate, have
    taken all the mainline courses and the non-duplicating electives.  So a
    power-boater would not have to take Seamanship Sail, for example.  USPS
    uses the grade SN, and CPS adopted this a few years back.
    CPS is about 40,000 members, 170 Squadrons.  And we party a lot here in
    District 9 (Western Ontario) with our "parents" in the USPS District 9 at
    District Rendezvous, etc.  We also have a standing agreement now, that any
    new course developed by one organization can be used by the other.   The
    ultimate in cross-border shopping!
    I have to feel for students and examiners that work with dip short sights.
    They add a lot more calculation, and require careful examination of a local
    chart extract that has to accompany the sights.  I have never gotten really
    good results with them, since many of the far banks of rivers, narrow
    lakes, etc., seem to overhang and darkness fakes out the actual water-land
    Jim and others (there are a few of us Canucks on the list) will correct any
    errors I've made.  Suffice it to say that there is still a lot of interest
    in CN among CPS members, with 5 in a class to start shortly here in London,
    and 3 in a class in Tillsonburg, a smaller nearby Squadron.
    P/Cdr John Kabel, SN
    London, Ontario
    > George:
    > I took this course more than a dozen years ago and was writing from
    > memory rather than having the actual sights in front of me.  You are
    > quite right to point out that my assertions about the ease of finding Lo
    > during a noon sight may have been a bit aggressive.  I recently moved and my
    > sights are buried somewhere in a large collection of as-yet unpacked boxes.
    > I value the integrity and expertise of this list and I'm going to withdraw
    > my claim until I can resurrect my sights and confirm my experience.
    > BTW, the US Power Squadrons standards for acceptable sights for their
    > courses are +/- 3 miles if taken on land, +/- 5 miles if taken at sea.
    > A bit of background on USPS for people unfamiliar with it -- it's the
    > largest public service group devoted to recreational boating safety in
    > the US.  Has about 60K members in 450 chapters throughout the country.
    > Does everything from vessel safety checks to teaching 11 different
    > courses, the latter running from simple deck seamanship through advanced
    > celestial.
    > I'm a USPS member and have to admire our volunteer sight folder checkers --
    > in both our basic and advanced celestial courses, each student is required
    > to submit a sight folder (roughly six different types of sights per course)
    > which must then be examined in detail and approved by a member volunteer
    > before the student can pass the course.  Since each sight is unique to time,
    > body, and sight location, there are no answer sheets the volunteer can refer
    > to, he/she must start with the student's sight data and go through the full
    > reduction using (a) the Nautical Almanac data (including all interpolation,
    > ugh, because NA interpolation may give slightly different answers for GP
    > than a computer program that solves the GP equations for the exact time
    > specified) and (b) the reduction method specified (calculators for the basic
    > course, sight reduction tables (to give experience with those) in the
    > advanced course).  Before submitting the sight folders to the official
    > grader they must be locally checked.   I've done this several times for my
    > local chapter and it's quite a task (and I've then gotten folders back with
    > things I missed marked off!)
    > Oh, and the oddball name "Power Squadron" (which I desperately hope they
    > will someday change since we're neither exclusively powerboaters nor a
    > quasi-military organization)?  It relates to pre WW I days when the group
    > started as the "power[boat] squadron" (vs "steam yacht") of the Boston Yacht
    > Club.
    > Lu Abel
    > George Huxtable wrote:
    > > Lu Abel wrote-
    > >
    > >
    > >>I don't know how many on this list have actually taken a noon sight.  I
    > >>have.
    > >
    > >
    > > But from on-land, it seems, when he says later "I also freely confess this
    > > sight was taken on dry land, so I wasn't dealing with trying to bring down
    > > the sun on a heaving ship's deck."
    > >
    > > It's quite a lot harder, and less accurate, when you observe a Sun
    > > altitude in real-life, at sea, above a real sea-horizon. Is an observation
    > > from on-land considered adequate by the US Power Squadron?
    > >
    > >
    > >>A noon sight is part of the requirements for US Power Squadron's
    > >>Navigation course (advanced celestial nav) which I have taken.  I found
    > >>(at ~40N Lat, sight taken during the early summer) that not only did I get
    > >>a spot-on latitude value, but by graphing a series of sights over about 10
    > >>minutes (5 min on either side of LAN) I got quite an excellent value for
    > >>longitude.
    > >
    > >
    > > I would expect a "spot-on" latitude value, just as Lu claims. But notice,
    > > he doesn't quote any actual figures for his "quite an excellent value" for
    > > longitude. I hope he will dig out his observation log and give us some
    > > real numbers.
    > >
    > > I have recalculated what Lu's observations should have been, taking an
    > > observer at 40 deg North, 0 deg West, and as an example of "early Summer",
    > > today's date of 4 June 05. The following altitudes include no correction
    > > for refraction, dip, semidiameter.
    > >
    > > Noon-by-the Sun occurred at 11h 58m 18s, when Sun alt. was at its maximum
    > > of 72deg 28.6'
    > >
    > > 5 minutes earlier, and also 5 minutes later, the Sun alt was 1.9' less, at
    > > 72deg 26.7'
    > >
    > > At those two times, 10 minutes apart, for which Lu will have to split the
    > > difference to find his moment-of-noon, the Sun is first rising, then
    > > falling, at 0.75 arc-minutes for each minute of time.
    > >
    > > How accurate are Lu's altitudes going to be, if measured in real-life at
    > > sea? I wonder if any one of us can put his hand on his heart and claim to
    > > be able to measure the altitude of a real Sun above a real horizon AT SEA
    > > within a scatter of, say, ?1 arc-minute. Here, I am referring to the
    > > small-craft situation; I accept that on a big-ship, in millpond
    > > conditions, somewhat less scatter than that might perhaps be achievable.
    > >
    > > If the altitude is changing at only 0.75 arc-minutes, each minute of time,
    > > at the extremes of Lu's time-range, and with a presumed scatter of ? 1
    > > minute in each observation, I really can't see how, with the most careful
    > > graph-plotting over those 10 minutes, a navigator will find the
    > > centre-of-symmetry of the resulting curve to better than, say ?1 minute of
    > > time. Not a very precise result then, when he might expect his chronometer
    > > to be good to a second. A scatter of ?1 minute of time corresponds to a
    > > longitude error of ?15'.
    > >
    > > Those error estimates seem fair to me, but I would be happy to argue the
    > > matter out if anyone thinks otherwise.
    > >
    > > Compare that with a time-sight measurement made several hours away from
    > > noon. If the Sun is on a path to pass overhead, then its altitude will
    > > change by 15 arc-minutes for every minute of time. From higher latitudes,
    > > the rate of rise will be less, but a properly chosen moment for a
    > > time-sight will normally involve the altitude changing by at least 7.5
    > > arc-minutes per time-minute (except in arctic latitudes). This is ten
    > > times faster than the rate-of-change that Lu observed, so given the same
    > > accuracy in observing altitude, the scatter in deduced time will be
    > > reduced by a factor of 10, to be 6 seconds of time. And that would
    > > correspond to a longitude error of 1.5 miles, not 15 miles: a substantial
    > > improvement, obtained by using the traditional time-sight technique.
    > >
    > > So if Lu really did get his unspecified "quite excellent value for
    > > longitude", I wonder if it was perhaps obtained by some sort of fluke.
    > >
    > > I don't deny that a noon Sun longitude can be made to work, to some
    > > extent. One distinct improvement would be to extend the period of
    > > observation, to be significantly longer than the 10 minutes around noon
    > > that Lu allowed himself. But if the time interval between the rising Sun
    > > and the falling Sun becomes great enough, the question then arises: can
    > > you call it a "noon observation" any more?
    > >
    > > Of course, from a moving ship, with any Northing or Southing in her
    > > course, there's another factor to consider, that didn't come into Lu's
    > > on-land observations. That motion gives rise to a displacement in time
    > > between the moment of maximum altitude (which is what's observed) and the
    > > moment of the Sun's meridian passage (which is what's needed). It isn't
    > > hard to correct for, but that correction should not be neglected. There's
    > > an additional, smaller, correction to make to allow for the Sun's changing
    > > declination, being greatest near the equinoxes, but that's usually small
    > > enough to neglect.
    > >
    > > George.
    > >
    > > ================================================================
    > > contact George Huxtable by email at george@huxtable.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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