There may be times when a navigation chart showing contours along the coast and/or navigational hazards is not needed. This is generally the case with celestial navigation, however, you may also find times while piloting along a coast that this is the case. An example might be that you prefer to keep your DR and Fix plotting off of the navigation chart in order to keep it more readable. Using a Universal Plotting Sheet allows you this flexibility.

Universal Plotting Sheets may be purchased in pads of 50, or they may be downloaded from the internet. Generally, they will include a compass rose in the center, three pre-drawn latitude lines, and one centrally located line of longitude. They are printed with “minute” marks (miles) for latitude and a scale to use in determining minutes of longitude. Having a pad on board is always a good idea.

Unfortunately, having a pad on board is not always the case, and “using the up” during practice can be expensive and frustrating. Fortunately, there is another solution. You can use any conveniently sized paper (e.g. 8.5 x 11) to make your own. I personally like to just use a blank notebook as a navigation log, and use a blank page in it to create universal charts as needed. Here is how.

Plot The Primary Latitude and Longitude Lines

Step one: Using a convenient size of paper (in this case, 8.5 x 11), draw a horizontal line and a vertical line at approximately the center of the page. Label the horizontal line with the desired latitude and the vertical line with the desired longitude. In the example, Latitude 39N and Longitude 122 W were selected.

Draw an Angle Representing Your Latitude

Step two: Draw an oblique (diagonal) line representing the angle equal to the center longitude line. Here, the line is drawn at a 39 degree angle from the horizontal line.

Mark the oblique line in increments equal to the scale you have decided to use. I chose to use a scale of 1/2 inch for every 10 miles. Six equally spaced divisions every 1/2 inch is equal to 60 miles, or 1 degree of Latitude.

Find Your Longitude Lines and Minute Gradations

Step three: Drop a vertical line from the sixth diagonal division mark to the center latitude line. This line marks the location of the next degree of longitude. Draw another vertical line an equal distance away from the center longitude line on the opposite side. Your universal plotting sheet now includes 2 degrees of longitude. A final part of this step is to drop a mark straight down from each diagonal division down to the center latitude line. Each mark on the latitude line is equal to 10 minutes of longitude and each mark on the oblique line is equal to 10 minutes (miles) of latitude.

Find The Latitude Lines Above and Below the Primary Latitude Line

Step Four: Using dividers, measure the length of the oblique line from the center to its intersection with the longitude line. Swinging the dividers so it scribes an arc across the longitude line above and below the center latitude line provides the limits of one degree of latitude above and below the primary latitude line.

Set Up The “Minute” Marks

Step five: Finally, graduate the oblique line into convenient units. In the example, each marking is 2 minutes (miles). And, graduate a section of the latitude line into similar units.

Your Universal Plotting Sheet Is Ready To Use

Good news! You are ready to go. As drawn your plotting sheet covers an area of about 180 mile (E/W) by 130 miles (N/S).

A small amount of practice is all you need to get proficient.

A Final Note

When using a universal plotting sheet, “standard” plotting tools may be a bit unwieldy. My personal preference is to use a 5 inch Douglass Protractor. It seems to be the perfect size to use with an 8.5 x 11 sheet of paper, and is conveniently marked off in 1/2 inch increments. As a bonus, each 1/2 inch is further broken down into 5 divisions, which can be used to represent 2 miles on the latitude scale. With those divisions marked on the plotting sheet is is very easy to interpolate into smaller distances.

What Are Pilot Charts?

Pilot Charts provide the navigator with averages. Averages concerning prevailing winds and currents, air and sea temperatures, wave heights, ice, visibility, barometric pressure, and weather conditions.

There are five volumes of Pilot Charts, each being its own publication, and each covering a specific geographic region. Each publication is actually a compilation of twelve individual pilot charts, one for each month of the year.

Pilot charts are intended to aid the navigator in selecting the fastest and safest routes with regards to the expected weather and ocean conditions. Pilot Charts are not intended to be used for navigation, however, they are invaluable in planning stages of a voyage.

https://msi.nga.mil/Publications/APC

Coverage Areas

Pilot Charts may be downloaded from the Maritime Safety Information Publications website.

As can be seen in the image below, there is a great deal of information contained in a pilot chart. Most of this information will be explored and interpreted as we move through this post. In this case, we will be looking at average conditions in the North Pacific Ocean in the month of July. One very nice feature of a Pilot Chart is that it not only contains the data, but also instructions on how to use and interpret the data. Pilot Charts are very much self contained.

The Main Body of the Chart

Wind Roses

As a sailor who primarily is interested in wind driven vessels, my primary concern when it comes to sailing is the wind. Will there be enough? Too much? What direction will it be coming from.

Fortunately, typical wind conditions is one of the primary pieces of information found on a pilot chart. Every 5 degrees (300 miles), east and west as well as north and south is a wind rose. Understanding the wind rose is critical to proper use of a pilot chart.

Wind Arrows

There is a wind rose sitting just offshore from San Francisco. Because of the land mass and printed information on the chart, it can be a challenge to read this rose, but let’s give it a try. We will start by looking at the wind arrows. There are eight of them, marking the cardinal (N,S,E,W) and intercardinal (NW, SW, SE, NE) compass points. The length of the arrow shaft tells you the percentage chance of wind from that direction (more on measuring it in a minute).

In this case, the arrow coming from the NW has the number 45 printed on it. Any time a wind arrow is “too long”, it is shortened to a set maximum length and the percent chance of wind from that direction is printed.

Also included as part of the wind arrow are “feathers” arranged on each side of the shaft. There are four arrows, two on each side. The arrows indicated the Beaufort force of the wind coming from the indicated direction. That one arrow now tells us there is a 45% chance of force 4 winds (11-16 knots) coming from the northwest.

The length of the arrows not labeled with percentages can be measured and compared with a scale found on the chart. A quick measurement with dividers provided an 18% change of wind from the north at force 5 (17 to 21 knots).

Calm Days

The final item relating to the wind rose is the number within the circle at the center. In this case, “8”. There is an 8% chance of a calm day (less than 1 knot of wind).

Wave Heights

Before we move to the next graphic, the is one more piece of information found in the graphic above. The red solid line indicates the percentage change of 12 foot or greater waves during the month. Directly off of San Francisco, it is statistically rare, but it may happen. However, a bit to the north there is a 10% chance of 12′ or greater waves.

San Francisco to Cabo San Lucas in November

Before we move on to the next topic, here is a quick planning exercise for an imaginary trip from San Francisco to Cabo in November.

Off of San Francisco, about 40% of the time the wind will be out of the N or NW at force 4, with calm days expected only 2% of the time. Waves of 12 feet or greater are expected 10% of the time.

Near Los Angeles, the wind will be out of the N or NW at force 4 about 76% of the time.

Nearing Cabo, the prevailing winds are still out of the N or NW over 70% of the time, however, the intensity has dropped to force 1 (1 to 3 knots)

Surface Currents

A new piece of information contained on the chart also presents itself in this exercise. The green arrows represent the expected current in the area. Mostly going down the coast on this trip, currents of .4 to .5 knots will help you on your way. However, if you look close, near shore north and south of San Francisco is a counter current heading north at .6 knots. Staying close to shore could add an extra 4 hours to your trip during the first 200 or so miles.

Two additional topics covered in the main body of the Pilot Chart that may not be of general interest to most sailors are the limits of ice during the month, and a plot of great circle routes (including distance) between a number of major ports. It is nice to know where they are, and the distance from place to place. San Francisco to Yokohama is 4452 and is composed of an arc starting at the 38th parallel, then traveling as high as the 48th parallel before dropping back down to latitude 35.

Average Weather Conditions

In the upper left of the chart is a general text description of the average conditions of wind and weather. Topics covered include:

• Winds
• Pressures
• Visibilities
• Gales
• Extratropical Cyclones
• Tropical Cyclones
• Air Temperature
• Wave Heights
• Average Ice Limits
• Frequency of Wave Heights

Sub Charts

In Addition, graphics of the topics shown above are included.

Air and Sea Temperature

A sub chart is included (not shown) indicating average air and sea temperatures in the area for the depicted month.

Ice Limits

Great Circle Routes