8 Points to Consider While Nautical Chart Plotting on Ships

In a recent article posted on Marine Insight, Nachiketh Bhattathiri discussed key factors that must be considered by deck officers to ensure error-free, efficient chart plotting. According to Bhattathiri, “[Chart work is] an imperative job which every navigating officer should master. It is also one of the top-tier skills which decide the competency of a ship navigator.” With that in mind, Bhattathiri wrote the following eight points to consider when nautical chart plotting on ships:

  • Scale of the Chart: The scale of the chart is the first thing to check before commencing chart work. The chart scale is given down below the name of the chart. “After taking a note of it, allow yourself to glance through the latitude and longitude graduations along the chart,” writes Bhattathiri. “Once you are familiarized with the scale, the chances to do a wrong plot are largely reduced. The depth scale of the chart should be considered as well.”
  • Notes of the Chart: Once you are aware of the scale, a navigating officer should read the notes, which are found below the chart name. The notes will provide important information about navigating through the area covered by the chart, including any submarine or naval exercise areas, anchoring, fishing areas, traffic separation schemes, any additional information about wrecks, tidal information, and also local regulations concerning navigation.
  • Chart Symbols: Navigation officers must have a thorough understanding of symbols and their meaning. When plotting charts, “out of ordinary” symbols should be noted and checked.
  • Chart Corrections: The Second Officer is responsible for keeping all charts up-to date with all permanent and temporary corrections received weekly via Notices to Mariners. The permanent corrections are marked on chart using magenta ink and temporary corrections are marked using pencil.
  • GPS Positions: According to Bhattathiri, navigation officers should avoid plotting GPS positions when navigating in coastal and restricted waters as such margins can be dangerous. Also, while navigating in shallow waters or near mountains, “multi-path errors” can occur, thus compromising the accuracy of the ship’s position.
  • Radar Fixes: “Radar fix is considered as the most reliable fix while navigating in coastal waters,” explains Bhattathiri. “Radar fixes are best when it is fixed using Radar conspicuous objects such as a Racon or Ramark. Racon and Ramark are indicated on the charts by a magenta circle and are easily identifiable on Radar too. It is recommended to notice them on charts and use for position plotting.”
  • Visual Fixes: Using lighthouses and other aids to navigation, visual fixes provide for reliable position while navigating near land. The bearings from the objects can be obtained using an azimuth ring. Such bearings should be quickly and carefully plotted on charts for best fixes.
  • Position Circle and Position Line: “Position Circle” is a circle drawn from an object (as its center) and its range from the ship as radius. Position Line is a line drawn from the object along its bearing from the ship, the ship’s position is known to be in that line. A fix can be obtained using two parameters (i.e., two position lines or two position circles or one position line/one position circle). The more parameters the better accuracy of the fix.

Bhattathiri concludes, “Chart work is a skill of accuracy and precision. The safety of navigations depends upon the quality and reliability of chart plotting. Hence the navigators doing chart plotting should do it with utmost care and attention. A wrong course line or position can mislead the vessel and can probably make way to accidents.”

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