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    Re: Should all electronic navigation devices on a yacht be set to True or Magnetic?
    From: Greg Rudzinski
    Date: 2009 Nov 17, 11:43 -0800

    Peter,
    
    When I purchased my current sailboat the previous owner informed me
    that the autopilot did not work. The autopilot looked to be in good
    condition so on a sea trial sure enough every time the autopilot was
    engaged the helm would go hard right. I suspected a magnetic influence
    but did not see a possible source within three feet of the unit. Out
    of curiosity I inspected the area on the opposite side of the bulkhead
    to find a stereo speaker! Moving the autopilot compass to a different
    bulkhead brought the unit back to life. So the autopilot may also need
    a Napier deviation card or two. New units today are suppose to
    automatically correct for deviation after circling a few times. A
    feature which I would find hard to trust.
    
    Greg
    
    On Nov 17, 6:39�am,  wrote:
    > The advantage of performing all one's chartwork and calculations in
    > degrees True is that it reminds you that your magnetic compasses are
    > not necessarily reading Magnetic, unless they have been compensated
    > exquisitely well.
    >
    > My small sailboat had no electronics until the late 1990's when I
    > bought a hand-held GPS. But from the first day I owned her I was
    > forcefully reminded of the need to allow for compass error. The
    > bulkhead-mounted steering compass was right over the engine's
    > starter/generator. When I fired up the Petter, the compass swung
    > 5 degrees east. So, not one, but two Napier diagrams are stapled
    > inside the cover of my workbook.
    >
    > [and although I'm sure it has nothing to do with age, I'm finding
    > that with each passing year the inner Magnetic ring of a coastal
    > chart's compass rose is harder to read than the outer True ring]
    >
    > �-- Peter Smith
    >
    > On Monday, November 16, 2009 8:16 PM,
    > David H. Smith  said:
    >
    > > When a yacht is first fitted with a GPS, I believe most owners choose
    > > to set it to "Magnetic Heading" so that when comparing the bearing to
    > > the steering compass, only deviation has to be considered. �However,
    > > in a short time, the amount of electronic navigation instruments
    > > grows and grows. �A fluxgate compass along with an autopilot and
    > > electronic wind indicators get fitted.
    > > Then are added a radar, a second GPS chartplotter, a handheld GPS, a
    > > PC chartplotter, an AIS and an AIS display unit.
    > > So eventually we have aboard a yacht almost a dozen navigational
    > > instruments (along with paper charts) capable of being configured to
    > > "True" or "Magnetic" and just two instruments - the steering compass
    > > and the handheld compass not being able to give a "True" bearing
    > > readout The steering compass and handheld compass are now far less
    > > important than they used to be, (but are vital if the power fails or
    > > in emergencies).
    > > Information given on charts, in tide tables and other publications
    > > are all in "True" bearings. � It seems to me that the traditional
    > > way of recreational sailing yachts having all electronic bearings
    > > displayed as "Magnetic" or "Compass", may not now be the most
    > > sensible thing. �
    
    -- 
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