Plotting Tool


Learning to navigate safely is arguably the most important skill to be learned in boating. The assurance that comes with knowing where you are and what lies ahead cannot be overstated. This manual is intended to start you on your journey to become a competent navigator.

This manual is for the beginning navigator. More in depth information is available and should be explored. The most popular reference for the weekend boater is, “Chapman Piloting”. All skippers should have one as a place to go for more information. While, “Chapman Piloting” is the most popular it is not the only reference and of course no reference will ever take the place of a good navigation class.

The Charting Pal, a NOAA certified chart and your GPS are the perfect combination keep you worry free on the water. I know of no other tool that is as easy to use or as accurate.

Only $5.99

Plotting Tool Instructions

Introduction

Learning to navigate safely is arguably the most important skill to be learned in boating. The assurance that comes with knowing where you are and what lies ahead cannot be overstated. This manual is intended to start you on your journey to become a competent navigator.

This manual is for the beginning navigator. More in depth information is available and should be explored. The most popular reference for the weekend boater is, “Chapman Piloting”. All skippers should have one as a place to go for more information. While, “Chapman Piloting” is the most popular it is not the only reference and of course no reference will ever take the place of a good navigation class.

The Charting Pal, a NOAA certified chart and your GPS are the perfect combination keep you worry free on the water. I know of no other tool that is as easy to use or as accurate.

Exploring Your Chart

The NOAA logo is your assurance that the chart you purchased is approved for navigation purposes. NOAA (National Oceanic and Atmospheric Administration) is the government body that is responsible for charting our waters.

Latitude and Longitude

Latitude is lines of position that run parallel to the equator. These lines are measured in degrees north or south of the equator. A typical reading would be N 45 30’. Each degree is exactly 60 miles. A minute of latitude is equal to a mile. That’s were the expression a mile a minute comes from.

Longitude is lines called meridians that slice up the earth from east to west. The prime meridian runs through Greenwich England and has a value of 0 degrees. All other meridians have a value of east or west of the prime meridian. A typical reading would be west 100 degrees 30 minutes. Here the minutes are not a mile as the distance increases as one approaches the equator.

The latitude and longitude lines are always in black on your chart. You must line up a red line on the Charting Pal with a black line on your chart. When navigating, the meridians are preferable as they always point true north.

The Compass Rose

The compass rose is found on all navigation charts. The most obvious job of the compass rose is to point to true north. True north is where the meridians end which co-insides with the North Pole. This is indicated by the outer ring of the compass rose. The inner ring of the compass rose contains your magnetic heading. The magnetic north pole is not located exactly at the North Pole. The closer one gets to the North Pole the greater the error factor. This error factor is called magnetic variation. If your look carefully at the center of your compass rose, you will see that the magnetic variance is known for your location. Also, that it is a constant number that must be added or subtracted from the true numbers one finds on the chart. Hint: if the numbers on the inner ring are greater than the outer ring we must add the variance to all our calculations to get a compass heading. If the numbers on the inner ring are smaller then we do just the opposite and subtract the magnetic variation to get our compass heading.

Mark your Magnetic Variation on the space provided on the Charting Pal so you will always have it close at hand.

The Distance Scale

Charts come in different scales. This is indicated by the distance scale of your chart. The larger the scale the less detail and the greater area covered. A chart that took you across the Gulf Stream to the Bahamas would have a larger scale than one you used inside Miami Harbor.

The Charting Pal has the most popular scales found on charts. All multiples of 40,000 to 1 can be read directly from the scale on the Charting Pal. Look at the scale area of your chart to see the scale of your chart is using.

Using Latitude Scale to Compute Your Distance

The latitude scale on the side of your chart has the following markings. The each degree is equal to 60 miles. We then further divide the scale by minutes. Each minute is equal to one mile. Looking at the minute scale.

We notice that there are tenths of a minute. Each tenth is equal to 600 feet. We can even divide it up further by estimating another decimal inside the tenths. This will give us our distance to within 60 feet.

Soundings Scale

Posted in large type on the top of your chart is the sounding scale. Your scale will either be in feet, meters, or fathoms. One fathom is equal to 6 feet. It is essential that you know your depth scale to keep from running aground.

Shallow Water

Most charts will have a color differentiating the shallows from the deeper water. The example below shows the shallow water colored blue and is less than 6 feet. Whenever you are in shallow water you must be vigilant of your position and your course.

Sandbars and Coral Heads

Sandbars and Coral Heads are noted with a special symbol. They can pop-up anywhere and are a prime reason to chart your course so that you can avoid these hazards to navigation.

Find Your Channels

Channels are safety zones that allow you to traverse shallow areas. There were put there to keep you from running aground. Whenever there is a channel present a prudent skipper will always stay in the channel.

Channel Markers

These symbols are called daymarks. They are signs affixed to poles that are set into the bottom of the bay or waterway. The triangle markers are always red and are even numbered. The green markers are always square and have an odd number on them. When we are on the Intracoastal Waterway, these markers may be lighted have either a yellow square or triangle on the daymark. Any markers can be lighted. The symbol for a lighted marker is the exclamation point. Here we have a marker that is lit.

Channel markers can also be the floating type. The red buoy is shaped like a cone on the top. Once again all red buoys are even numbered. The green markers are shaped like a 55 gallon drum. Hence the name can buoy. They are either green or black; odd numbered and can be lighted. Once lighted the buoy description is the same as the daymarks.

A good way to stay out of trouble is to remember Red Right Return

Which means keep the red marks on your right as you enter the channel from the sea.

Finally, the purpose of the channel marker is to pin point your position, just as a street sign, so that you can plot a safe route to your destination.

Plotting a safe course

Let’s plot a course. Before we begin there are some things you must consider. The first is that each segment is called a leg. Each leg must start from a known point, called a fix, and go to another known point. The easiest way to accomplish this is to find a channel marker and use it for each end of your leg.

Draw a line on your chart. This will be the first leg on your trip. Examine the line carefully. Are there any shallows on or near our course? Are there any obstructions that need to be avoided? Sometimes it is impossible to go directly to your destination. The example below shows that very often we need several legs to get to our destination.

Measure your course

Place the center of the Charting Pal so that it rests on top of your course line at the beginning of your leg. Find a latitude or longitude line that corresponds to a red square on the Charting Pal. You can now read your course heading on the outer ring of the Charting Pal.

When lining up your tool with the black lines on your chart it is preferable to use the longitude, as it is always pointing north. That said, latitude lines work just fine.

Using the example above we have a course heading of 130 degrees. This number is called a true course number.

Magnetic Variation

Your chart points to the North Pole. Your boat compass points to the Magnetic North Pole. This difference is called Magnetic Variation. The closer we get to the North Pole the more pronounced the difference.

While Magnetic Variation sounds complicated it is a simple computation to convert your True Course number into a Magnetic Course heading that your compass uses to get you to your destination.

Finding the Distance

Check the scale on your chart. If it is 40,000 to 1, 80,000 to 1 or 160,000 to 1, we can then use the scale that is on the side of the Charting Pal. In this way by measuring our course line we can determine our distance.

If the scale of your chart is not a multiple of 40,000 to 1, we can still accurately compute our distance.

Using the millimeter ruler on the side of the Charting Pal you can measure your course line. Then it is a simple matter to read your distance from the Latitude Scale on the side of your chart.

Each gradation on the side of your chart is equal to one minute. This is further broken down into tenths and on most charts we can guesstimate another tenth. This would make our distance measurement accurate to one hundredth of a mile or 60 feet.

Once you have this number, write it under the course line with the letter “D” after the number. This way it will not be confused with the course heading.

Marking Your Chart

There are some conventions to marking up your chart. The main reason to use these conventions is that anyone can pick up your chart and know instantly whether the course is true or magnetic.

Course Heading is always marked above the line using 3 digits. If there is nothing following the number then we assume that the course is a true heading. It is a good idea to mark all your course numbers with a “T” for true or “M” for magnetic so there cannot be any misunderstandings.

Distance is marked under the course line using one decimal place. Place the letter “D” after the number so it cannot be confused with any other marking on your chart.

Speed is marked under the line with one decimal and the letter “S” after it. All nautical speed is assumed to be in knots. One knot equals 1.15 MPH.

C 082 M

D 7.4 S 10.3
C= Course
M= Magnetic
D= Distance
S= Speed

Reciprocal Course

When returning on a known course heading it is a simple matter to compute the reciprocal course heading. If the original course was less than 180 degrees we add 180 and if the original course was more that 180 degrees we subtract 180 degrees. If you draw your course line through the center of the compass rose you can determine your reciprocal heading that way. Finally, using the Charting Pal you can easily place it on the other end of your course leg and read the reciprocal course on the outer ring.

Finding Your Position Using Triangulation

Take two compass reading from your vessel to known positions on land.

This is best accomplished by using a hand held compass Write down the heading toward your landmark. Note this is a magnetic number and will have to be converted to true number before we can transfer onto our chart.

We must find the reciprocal course from the landmark to your vessel. For example, if the course to the object is 30 degrees, add 180 and we get a reciprocal course of 210 degrees. If the course to the mark is 210 degrees we would subtract 180 and get a reciprocal course of 30.

Before we can draw our reciprocal course we need to convert the magnetic course to a true course. Once again we need our magnetic variation. However in this case if we added the number before, we now have to subtract to convert from magnetic to true. Remember – All Lines on a Chart must be True Numbers.

Place the center of the Charting Pal on the object we have been sighting on. Then using a straight edge find the true number on the outer ring of the Charting Pal. Mark the point on your chart. Now, draw a line from the object on land to the point on your chart.

Repeat the procedure for the second point you have observed. After you have drawn your second line you will observe that the lines have intersected. Where the two lines intersected is your exact location. This position is called a Fix. It is noted on your chart like this.

It is now a simple matter to draw a course line from your known position to your destination.

Using your GPS

All GPS (Global Positioning Satellites) units work exactly the same. They obtain a fix on 3 or more satellites that are orbiting the Earth. Once the GPS has determined its location it will display the information using Latitude and Longitude numbers.

A chart plotter unit will overlay a Chart on top of the Latitude and Longitude information. This wonderful as long as it is working and the screen is large enough and bright enough to be seen in all conditions.

The Professional Captain will never rely on one data source. Most carry a simple handheld GPS will all their waypoints entered. Then it becomes a simple matter to create a route using these waypoints. Routes employ the “goto” command. A highway or large arrow will then direct you to your next waypoint. These screens are much easier to read and don’t require any interpretation by the helmsman.

The mechanics are basically the same as above. Draw each leg of your course. Enter the latitude and longitude of each end point of your leg. Finally, you can combine these waypoints into a route. It’s a very simple procedure and one that can have a big payoff in safety once conditions deteriorate.