Charting, the three basic exercises to have fun on cruise

Although chartplotters and GPS have taken over, one must always be prepared for charting with a square, compass, surveying compass, and nautical chart. Also because in case of a power outage on board, you will have to deal with it the old-fashioned way. Most importantly, these are exercises you can have fun with this summer on a cruise.

Let’s review the charting

From our archives, we have selected three charting exercises for you to refresh your memory if you already have a boat license, or very useful as a first smattering of charting!

Charting – 45° and traverse survey

This detection is used when there is only one conspicuous point(those particular natural conformations or constructions-lighthouses, etc.-that have the characteristic of being easily detected and observed from a distance) to be detected.

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In the example above you are in the Gulf of Tigullio, heading 360° toward land.

• Plot the estimated route (Rs) on the chart. The lighthouse of Punta Portofino is visible on the left.
• Using the surveying compass, sight (sighting: observing an object between the two aiming points of an instrument so that it is aligned with the line of sight) the beacon until you detect it at a 45-degree angle to the course (315 degrees).
• Draw a straight line from the Portofino lighthouse. (A) reaches Rs (point B) at an angle of 45°.
• Annotate the log and continue tracking the beacon until you detect it at 90° (270°).
• Now draw a straight line from the Punta Portofino lighthouse (A) to our estimated course (C) at an angle, relative to our course, of 90°.
• Note the log again and check the miles traveled (1.3 miles).
• Compass a distance of 1.3 miles from A to C on the map.
• The new point on the chart represents the True Point (Pn, with Rv standing for true course).

Charting – The collision course

When you encounter another vessel in the middle of the sea, to quickly tell if you are on a collision course you must first maintain a constant speed and course for the time it takes to detect it.

• Once you believe the other boat is in turn maintaining a steady course and speed, with the bearing compass, survey the approaching boat.
• Repeat about every 5-10 minutes.
• If the bearing will be constant, it means that if neither commander changes course or speed the collision is certain.
• Slow down, speed up or change your course by a few degrees, remembering that between two motor boats the one coming from starboard takes precedence, between a motor boat and a sail boat the sail boat always takes precedence. In any case, even the boat with the right of way must still keep “out of the way.”

Ship point with three conspicuous points

This is the most effective way to understand one’s position. A chart and a surveying compass are obviously needed. What is obtained is still not a “certain point” but a “probability zone” within which our position is estimated.

• In the example we are sailing with estimated course (Rs) 224° toward Bastia, Corsica.
• The three points to be surveyed are the Punta del Trattolo lighthouse on Capraia Island, the Giraglia rock lighthouse on the tip of the Corsica finger, and the Cape Sagro lighthouse, which we know is about 7 miles north of Bastia.
• Once the three surveys are plotted on the map, you will get not a precise point but a small triangle.
• This area, called the “probability triangle,” will be the area within which you estimate your position.

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