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Safe Boat Operations – Basic Plotting Equipment

Source: Mariners Learning System, by Captain Bob Figular

Adequate preparation is very important in piloting a boat. Piloting is the primary method of determining a boat’s position by using landmarks, other navigational aids, and soundings. In order for a boat operator to be able to use good judgment on all decisions with regards to navigation the proper tools and publications must be onboard and readily available. Therefore, it is important to be alert and attentive, and always be consciously aware of where your boat currently is and where it soon will be.

Boat operators should never get underway without the appropriate charts or the following plotting tools:

  • Charts are essential for plotting and determining your position, whether operating in familiar or unfamiliar waters.
  • Parallel rulers are two rulers connected by straps that allow the rulers to separate while remaining parallel. They are used in chart work to transfer directions from a compass rose to various plotted courses and bearing lines and vice versa. Parallel rulers are always walked so that the top or lower edge intersects the compass rose center to obtain accurate courses.
  • Dividers are instruments with two pointed legs, hinged where the upper ends join. Dividers are used to measure distance on a scale and transfer them to a chart.
  • A stopwatch is very useful to find the lighted period of a navigational aid. This is usually done for purposes of identification. Also it may be used to run a speed check.
  • It is important to use a correct type of pencil for plotting. A medium pencil (No. 2) is best. Pencils should be kept sharp; a dull pencil can cause considerable error in plotting a course due to the width of the lead.
  • Light lists provide more complete information concerning aids to navigation than can be shown on charts. They are not intended to replace charts for navigation and are published in seven volumes.
  • Tide tables give daily predictions of the height of water, at almost any place, at any given time, and are published annually in four volumes. Instructions for using the tables are provided within the publication.
  • Tidal current tables provide the times of maximum flood and ebb currents, and times of the two slack waters when current direction reverses. They also tell the predicted strength of the current in knots. The time of slack water does not correspond to times of high and low tide. The tide tables cannot be used for current predictions. The tables are published in two volumes. Instructions for using the tables are provided within the publication.

The amount of information that can be printed on a nautical chart is limited by available space and the system of symbols that is used. Additional information is often needed for safe and convenient navigation. Such information is published in the Coast Pilot. These are printed in book form covering the coastline and the Great Lakes in nine separate volumes.

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