Seamanship_Secrets_185_Tips_-_Techniques_for_Better_Navigation-_Cruise_Planning-_and_Boat_Handling_Under_Power_or_Sail_(Re)_e..

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chart plotting and preparation 37


navigational equipment consisted of a magnetic compass, chart, and radar.
As we cleared the jetties, the pre-plotted tracklines and compass weren’t jibing
at all. As a matter of fact, the compass consistently read 5 or 6 degrees high
or low, depending on our heading. Luckily the disabled vessel was only a few
miles offshore, and we picked them up on radar, but I was determined to
solve the mystery back at the docks. As it turned out, a tiny 2-inch flathead
screwdriver had dropped into a slot behind the compass mounting.
Always mount the compass in a location several feet away from electronic
instruments, including depth sounders, radar, VHF radio, or GPS receivers.
Also, check your jewelry, knife location, cell phones, calculators, cameras,
wire-rimmed glasses, earrings, necklaces, stereo speakers, and anything
else close to the compass. Keep metals and electronics 36 inches from the
compass, if practicable. If that’s not possible, minimize electrical interference
by twisting electronic instrument wiring beneath the console or binnacle
housing. Twisted wire pairs cancel each other’s fields and leave your compass
free to do its job.
Every boat needs its compass periodically checked for deviation. After
making a course change, get into the habit of checking the deviation. Use a
handbearing compass for comparison against any steering compass.


HOW TO CONSTRUCT A DEVIATION
TABLE FOR ANY BOAT



  1. Turn on standard equipment. Energize any electronics that you normally
    use while underway, such as radios, GPS, chart plotter, or radar.

  2. Find your boat’s deviation-free zone. To fi nd deviation, you must fi rst
    locate your boat’s deviation-free zone, or DFZ, a spot that is completely free
    of magnetic infl uences. On power vessels, move aft of the console or into
    the cockpit. On sailing vessels, move aft toward the backstay. On any boat,
    stay as close as possible to the boat’s centerline. Find a distant object at a
    range of 1 to 2 miles. It’s not necessary that the object be charted, as long as


SEA-CRET TIP


X Many small-craft navigators prefer to plot in degrees magnetic.
It’s a personal choice, but use care not to mix true and magnetic
tracklines or bearing lines. Consistency is the key. Plot all lines
using magnetic directions or all lines using true directions.
Free download pdf