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    Re: DR plotting techniques
    From: Jim Thompson
    Date: 2003 Oct 16, 17:08 -0300

    This could be an interesting thread.  OK, I'll be honest, although I feel
    nervous sticking my neck out. Don't expect Navy/Merchant Marine/Coast Guard
    nav procedures on our bridge.  No doubt I'll learn from reactions to this.
    Recreational boater, coastal marine tidal waters, 30' twin screw family
    power cruiser, two helm stations, and usually steer on the flybridge.  We
    never travel out of sight of land, unless rain obscures the horizon in
    mid-Strait during a crossing.  We do not range more than 200 NM from our
    home port.
    1. GPS chartplotter and laptop with track recording, supplemented by radar,
    sounder and magnetic compass (one at each of our two helm stations).
    2. I keep paper charts handy at the helm station, but we do not have a chart
    table, so I keep the charts in big plastic envelopes, each folded to the
    portion of water we will travel.  I have a dozen such envelopes.  At the
    beginning of each summer I preload them with the appropriate charts, folded
    to the area we will be cruising.
    3. I do not attempt to plot a record of tracklines or draw bearings on the
    paper charts, although I do that on the laptop sometimes.  I never draw on
    the paper charts.
    4. Sometimes I take rough bearings on navaids or landmarks using our
    compass-equipped binoculars, then roughly transfer them with the edge of my
    hand to the compass rose on the paper chart.
    5. I sometimes jot informal notes in a reference binder that I keep at the
    helm station, but I do not formally log periodic positions in lat/long
    coordinates.  Just, "1015: rounded Cape Bear, winds SW 15, waves astern and
    lumpy with ebb, SOG 8 knots, 2600 RPM".  At the end of each day, when we tie
    up or anchor, I save the trackline to the laptop's memory.  I can replay the
    trackline anytime to show heading, speed and position.
    I've taken all the Power Squadron courses, and I was at the Coast Guard
    College in younger years, so I understand formal DR procedures.  But they
    are not very practical in our kind of cruising, on our kind of small boat.
    I keep the parallel rules, dividers, drawing compass and etc on the boat in
    a drawer.  However if the electronics go down then I am prepared to start
    using them, and as we cruise along I am always "thinking in DR" as a I
    gather information from the chartplotter, radar and sounder, and as I
    periodically check the paper charts while steering.  The GPS' trackline is
    very useful.  I have worked out deviations for our two compasses, but never
    have to steer by compass alone.
    Most recreational cruisers in our area are not trained in formal DR
    procedures, and some do not even carry paper charts for local runs.  Those
    that do often seem to use them the way we use roadmaps while driving a car
    on roadways.  I don't know anybody who uses parallel rules here.
    "Thinking in DR" is an interesting way to put it, I guess.  Having done all
    those laborious DR plotting excerises in course work, I find myself mentally
    using those procedures when I look at the instruments or study the wind and
    waves to picture leeway/current.  The more one knows about DR, the better
    one's position sense.
    Jim Thompson
    Outgoing mail scanned by Norton Antivirus
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Royer, Doug
    > Sent: Thursday, October 16, 2003 3:15 PM
    > Subject: DR plotting techniques
    > I would like to ask the members of the list who sail or pilot
    > power vessels
    > how or what techniques they use to find their DR pos. while underway.I am
    > only interested in what methods you use and don't wish to get into a
    > discussion of accuracy as yet.
    > 1.Do you use paper charts,rules and dividers?
    > 2.Do you use mathematical methods such as the following:Lat=Lf + -
    > e[S/60(cos T*)] ; Lon.=Lon.f + - e[S/60(sin T*/cos Lf)]
    > 3.Do you use chatplotters and gps?
    > 4.Do you use a computer or laptop with navigation software and gps?
    > 5.Do you use gps only?
    > 6.Any other method not listed above or a combination of the above.
    > Steven,thanks for telling me your training.In future conversations I now
    > have a baseline and know how to frame my questions or discussions with
    > you.By the way,thanks for the work you did on the Lunar files.I
    > hope to make
    > some use of them.
    > Jared and Dave,I'll get the brand name of the LED nav. lights
    > when I get to
    > the yard this week to work on the skiff and post that info.

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