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

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72 seamanship secrets


There are five essential ingredients for hassle-free dead reckoning:


  1. Known position. All navigation begins from a known position, whether
    a buoy, a jetty, or any other means of positive identifi cation.

  2. Trackline. A trackline, labeled TR, extends from the known position in the
    desired direction of travel. Plot the TR boldly to make it stand out from
    other plotted lines. We hope our boat stays on the TR, but forces such as
    wind and current, or our own steering errors, can move the boat off the TR.
    The connection between your boat and its TR changes all the time.
    At any given time, your boat is in two of six relationships to its trackline:


on TR
to the right of TR
to the left of TR
moving at its predicted speed
moving faster than expected
moving slower than expected

Once you have established your boat’s relationship to its trackline, you can
decide on a course of action. In some cases, being off the TR isn’t at all
critical, and the boat can continue in safety. At other times, being off the
TR by a few yards might place the boat and crew in danger.


  1. Steering course (C). Th e steering course, or courseline, is the course steered
    by the helmsman. Sometimes wind, current, or steering error can move a
    boat off its trackline. Th is means you might very well have to steer a diff erent
    course to return to the trackline. In Chapter 5 we’ll fi nd out how to tell this
    and how to correct for it. If the TR is 90 degrees but you are steering
    85 degrees to compensate for a south-setting current, you plot two lines on
    the chart. Draw the trackline boldly and label it TR—090oM. Th en draw the
    85-degree courseline with a lighter solid or dashed line and label it C—085oM.

  2. DR positions require time, speed, and distance. From the last known
    position, plot dead reckoning positions along the trackline (or tracklines)
    being steered. If you are steering the TR, plot DRs along the trackline.
    Otherwise, plot them along the steering course.


Time: Pick a time interval based on your proximity to danger or
uncertainty of position. Within a mile or two of the coast, use a
frequency of every 15 or 30 minutes. Off -soundings (when you are
off shore), use an interval of an hour or longer.
Speed: DR speed is usually taken from speed tables, a knotmeter, or a knot
log. Vessels under power can use a speed/RPM table (see Chapter 3). Vessels
under sail should use the knotmeter or knot log and take an average
of readings. As mentioned in Chapter 3, the speed these methods
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