1. Welcome How to Use a Chart Presented by United States Power Squadrons®
All Maps and Charts courtesy of MapTech
Welcome –
This Seminar will last approximately two hours and is presented by Members of United States Power Squadrons.
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2. Welcome I am Harry Hebb, SN Also Ron Swope, SN
Presented by United States Power Squadrons®
All Maps and Charts courtesy of MapTech
Welcome –
This Seminar will last approximately two hours and is presented by Members of United States Power Squadrons.
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3. How to Use a Chart
This Seminar is intended to serve as an introduction to basic chart symbols and use.
Chart Symbols
Chart References
Compass Rose
Locating a position
This Seminar is intended to serve as an introduction to Charting Skills. It is not intended to be a complete or comprehensive Course on understanding Charts, rather it is intended to inspire you to learn more about it. One should seek to learn more by taking a Boating and a Piloting Course to expand your knowledge of Charts. Very Good Reference Books for understanding the principals of Charts and Piloting are: Weekend Navigator by Bob Sweet and How to Read a Nautical Chart by Nigel Calder.
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4. The Marine Chart >> Large Scale Chart –
Larger scale charts display smaller areas in greater detail. In this case, a 1:20:000 chart, is used to show coastal details and entrances to harbors.
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5. Sources of Charts Hydrographic Offices Commercial U.S. – NOAA – NOS
U.K. – British Admiralty Charts
other…
Commercial
Maptech
Richardson’s
A good source of charts:
The list on the slide are producers of Charts that can usually be purchased at your local boating store or chandlery or ordered from Nautical Book Stores.
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6. More Detailed Information
For a complete list and explanation of all NOAA chart symbols, consult NOAA Chart Number 1, Nautical Chart Symbols Abbreviations and Terms … over 100 pages in the most nauseous of detail. Currently on-line only.
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7. What Charts Show Navigators
Above the Water
What Charts show:
above the water line.
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8. Colors Used on Charts White Blue Green Gold Magenta Deep, safe water
Shallow water
Areas covered at high water, bare at low water. Green buoys
Dry land, above mean high water
Lighted aids, boundary lines for special areas
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9. Features Above the Water
Even though a chart is intended to present you with a view of the water, your visual frame of reference while on the water is mainly provided by the land and landmarks around you.
Vertically recognizable landmarks are accurately plotted and labeled to help in identification. These can be used to help you locate your position by taking bearings to them. Landmarks (a circle with a dot in the center) are ACCURATE POSITIONS.
Objects with heights that are of importance are labeled. Their heights reflect their height above Mean High Water (MHW).
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10. Chart Information Source Chart Correction Date
Depth Units
Chart Scale
Mileage Scale
Horizontal (position) Datum
Chart Information
Each chart provides information essential for the navigator. In addition to the scale of the chart and its reference datum, you will find source information, its revision date, and the depth units. The chart’s compass rose provides valuable “variation” information.
Most nautical charts are calibrated in degrees, minutes and tenths of minutes of latitude and longitude. The latitude and longitude scales are shown on the degrees of charts. These are used for plotting accurate coordinates on the chart.
The latitude scale can also be used to measure nautical miles. One minute of latitude corresponds with one nautical mile of distance. CAUTION: Do not use the longitude scale to measure distance.
NM = 6, ft
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WGS .. World Geodetic System

11. Chart Features Compass Rose >> True North Variation Reference
Annual
Change
Magnetic
Scale
True North
Compass Rose
Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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12. Chart Scales
Chart Scales
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13. Chart Scales Charts are scaled representations
Scale is expressed as a ratio
Example: 1:40,000:
One inch on chart = 40,000 inches on Earth (.6 nm)
Typical scales
Sailing Chart 1: 600,000 … ? Small Scale
General Chart 1: 200,000
Coastal Chart 1: 80,000
Harbor Charts 1: 40,000
1: 20,000
1: 10,000
1: 5,000 ……. ? Large Scale
Chart Scales:
The grid on the chart provides a frame of reference. The placement of the latitude and longitude lines on the chart are based on a standard. On NOAA charts, North American Datum 1983 (equivalent to WGS 84) is the most common reference. The grid is aligned to true north, so the lines run north-south and east-west.
A chart’s scale is expressed as a ratio. For example, on a 1:40,000 scale chart, one inch on the chart represents 40,000 inches on the Earth (about one half of a nautical mile).
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14. Small Scale Chart - 1:1,200,000 >>
Examples of Different Chart Scales –
Small Scale Chart - Charts are compiled in a range of scales of increasing levels of detail. They are described by a ratio which describes the amount by which the real world have been compressed to fit on the chart. For example, in the chart shown, the scale is 1 to 1,200,000. This means that 1-inch on the chart is equivalent to 1,200,000 inches in the real world, or 100,000 feet, or 16.5 nautical miles. This chart shows a considerable area and is used for planning trips of some distance.
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15. Coastal Chart – 1:80,000 >> Coastal Chart –
This chart is a larger scale that is used to display major bays and medium sections of shoreline.
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16. Harbor Chart – 1:40,000 >> Medium Scale Chart –
A 1:40,000 chart is used to display bays and reasonable navigation features around land.
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17. Harbor Chart – 1:20,000 >> Large Scale Chart –
Larger scale charts display smaller areas in greater detail. In this case, a 1:20:000 chart, is used to show coastal details and entrances to harbors.
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18. Harbor Chart – 1:10,000 Large Scale Chart >> Harbor Chart –
Prominent harbors will have harbor charts of larger scale such as 1:10,000 shown or 1:5,000 which show in great detail the entrances and even docks within individual harbors including fine grain soundings.
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19. What Charts Show Navigators
Below the Water
What charts show Below the water.
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20. Charts Help Us “See” What’s Below
Charts Help Us “See” What’s Below the water
Courtesy Maptech
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21. Features Below the Water
Under the water, the depths and bottom contours are of importance to the boater. It is what determines where you can and cannot go while on the water.
Your job on the water is basic: navigate between the hills whose tops may be less than the depth needed for your boat. Your chart provides a two-dimensional picture of the bottom structure which you can plan travel that avoids the shallow areas.
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22. Depths SOUNDINGS >> [vertical numbers] Depth Soundings
at true position
Least depth in
Narrow channel
[number in parentheses]
SOUNDINGS
No bottom
at depth shown
Depth Soundings
Sounding are referenced to a particular water level (chart datum). Most NOAA charts use MLLW (Mean Lower Low Water). The specific reference is found in the chart legend.
Drying heights above
chart datum (green)
[number is underlined]
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23. Depths FAIRWAYS, AREAS >> Limit of dredged channel
Depth & year of
latest control survey
FAIRWAYS, AREAS
Unsurveyed
or inadequately
surveyed area
Depth Soundings
Fairways or channels are identified by dashed lines, some marked with depth as of a date and may be in shoaling areas and should be checked using Notice to Mariners or local knowledge.
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24. Nature of the Seabed Stones, gravel or shingle Rocky area Coral reef
These areas are generally marked with a description of the conditions on the bottom. This may be important to a boater when anchoring.
Coral reef
Green: area that covers
and uncovers
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25. Rocks >> Nature of the Seabed
What you can’t see can hurt you. It’s not just a shallow bottom that presents risk to the boater.
Running aground on soft mud may cause inconvenience, running into rocks may sink your boat.
All of the symbols shown are used for objects that could be dangerous to navigation. Avoid these areas. An object that is neither a rock or wreck is called an “Obstruction.” This may be a piling or stump or other hazard.
When you plan your trip, make sure to leave an extra safety margin around any of these objects.
These areas are generally marked with a description of the conditions on the bottom. This may be important to a boater when anchoring.
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26. Land, Rocks, Wrecks & Obstructions
These are some of the symbols you will find on a chart and what they represent.
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27. Depths and Heights >> Depths and Heights
The depth of the water is not constant in any area. Tidal areas may change by a few feet to tens of feet depending on where your are.
All depths on the chart are referenced to a common water level. Mean Lower Low Water (MLLW) is the reference used on most U.S. charts. MLLW is an average of the lowest daily water levels over a period of years. It’s important to note that MLLW isn’t the lowest possible water level.
Heights and vertical clearances generally are referenced to Mean High Water also an average. This can cause some confusion because depths are referenced to a low water standard.
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28. Charted Depth >> Charted Depth
In this example it seems that the boat has 2 feet of clearance. You must remember to account for wind and other factors that can affect water levels.
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29. Aids to Navigation (ATON) Son of ATOM … he, he
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30. Navigation Chart Symbols
Shown are examples of Common Chart Symbols.
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31. Navigation Aid Symbols
Chart
vs.
Reality
The object as it appears on the water is shown to the left of its symbol
Navigation Aid Symbols –
Navigation aids have shapes and colors that reflect their location and purpose. This figure shows a typical configuration of navigation aids for a boat returning from sea, or traveling clockwise along the coast of the U. S. There are two types of navigation aids: buoys which float and beacons which are affixed to the bottom or land.
Buoys are indicated by a diamond shape with a circle. The circle marks the approximate location of the buoy. The circle indicates that the buoy will move slightly about its mooring. A lighted buoy is indicated by a magenta disc around the circle. Beacons are indicated by a magenta flare with a solid dot marking the location.
There are several types of navigation aids. Those of lateral significance have colors and shapes corresponding to the side of the channel that they mark. Red will be found in the U.S. on the right side of the channel while returning form sea (on the left in Europe). Red navigation aids have even numbers and will have a conical shape, except for lighted buoys that tend to share common tower structures. All red navigation aids are painted red. If a red buoy is conical, it will be labeled with an “N” to indicate a nun. Some fixed red marks will be triangular. Green navigation aids have odd numbers and are cylindrical or square in shape unless it is lighted and sharing the same structure type as the reds. All green navigation aids are painted green (some exceptions are black). If these aids are lighted, they have varying patterns so that you can easily distinguish the proper aid at night. All red marks have red lights. All green marks have green lights. The pattern of the light is indicated on the chart. Typically, they will flash at a repetitive rate. The interval of the flash is shown on the chart. The figure shows the appearance of representative navigation aids on the water and their corresponding chart symbols. The Light patterns also are shown and described with the chart symbols.
Those navigation aids that mark safe water or the center of the channel are painted vertically red and white. If they are lighted, they will flash a white light with a Morse Code “A” which is a short flash followed by a long flash.
Variations of the red and green navigation aids are used where there are two channels to mark the preferred channel. They use alternating colors with the color on top that reflects what you would expect to see for the preferred channel (e.g., keep the red on the right when returning from sea). You can take the alternate channel, but understand its limitations by examining the chart. If lighted, these navigation aids flash the color of the top band in a 2+1 pattern (e.g., two flashes followed by a single flash shortly thereafter).
Navigation aids marking danger areas generally will be black over red with two black balls over the tower structure. If lighted, these aids will exhibit white lights usually with a pattern of multiple flashes.
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32. Finding Your Way by using Piloting Piloting typically refers to navigation by using land based objects as opposed to celestial bodies.
Finding Your Way
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33. Mercator Projection Chart
Latitude and Longitude
Latitude and Longitude represent your street address on the Earth. These coordinates are referenced to a specific mathematical model for the shape of the Earth (datum).
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34. Mercator Projection Chart
Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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35. Latitude and Longitude
Latitude and Longitude represent your street address on the Earth. These coordinates are referenced to a specific mathematical model for the shape of the Earth (datum).
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36. Coordinates Latitude N W Longitude >> Coordinates
Latitude is measured from 0° at the Equator to 90° North or South at the poles. Longitude is measured from 0° at the meridian that goes through Greenwich, England, to 180° East or West where they meet in the Pacific Ocean. The International Date Line.
W Longitude
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37. Measure Latitude >> Measure Latitude
Place a point of your compass on the waypoint and place the other on the closest printed line of Latitude, lift the compass being careful not change or move the compass legs, place the points on the scale on the left or right side of the chart. Read the latitude scale.
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38. Measure Longitude >> Measure Longitude
The procedure is the same as the previous slide using the Longitude scale at the bottom of your chart.
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39. Measure Course
Demonstration of Measuring a Course:
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40. Compass Rose >> True North Magnetic Scale Variation Reference
Annual
Change
Magnetic
Scale
True North
The Compass Rose:
The difference between the directions of geographic north and magnetic north is called “variation” and is displayed in the Compass Rose on your chart. Note the Variation on the slide is 4° 15’ W and the date that reading was printed.
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41. Chart Features Magnetic Poles >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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42. Chart Features Magnetic Variation >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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43. Chart Features Magnetic Variation >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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44. Chart Features >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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45. Chart Features Magnetic Deviation >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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46. Chart Features Magnetic Deviation >> Chart Features cont’d
The Compass Rose indicates True North and True Bearings, Magnetic North and Magnetic Bearings, Variation at a particular time and how much change in time.
The Compass Rose serves as a handy plotting guide.
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47. True versus Magnetic Location of Magnetic North changes over time
Difference is called “Variation”
Location of Magnetic North changes over time
Variation
East Coast - Magnetic North is to the West of True
West Coast - Magnetic North is to the East of True
Source of Information
Compass Rose
Variation –
Amount – East or West ‘as of [date]’ and ‘annual change’
Variation
Flash back to slide 36 to demonstrate graphically why there is a difference.
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48. True versus Magnetic T … true V … variation M … magnetic D … deviation
C … compass
Variation
Flash back to slide 36 to demonstrate graphically why there is a difference.
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49. True versus Magnetic True Virgins Make Dull Company … Add Whiskey
+ W or – E … from True to Comp
- W or + E … from Comp to True
T … true
V … variation
M … magnetic
D … deviation
C … compass
Variation
Flash back to slide 36 to demonstrate graphically why there is a difference.
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50. True versus Magnetic T … ?? V … 4 W M … ?? D … 0 deg C … 360 deg
Variation
Flash back to slide 36 to demonstrate graphically why there is a difference.
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51. Compass Rose >> True North Magnetic Scale Variation Reference
Annual
Change
Magnetic
Scale
True North
The Compass Rose:
The difference between the directions of geographic north and magnetic north is called “variation” and is displayed in the Compass Rose on your chart. Note the Variation on the slide is 4° 15’ W and the date that reading was printed.
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52. Planning on Your Chart
Planning on your Chart:
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53. Planning You want to go here (DESTINATION) You are here (START)
Planning ahead using the tools you have will give you important information you need to make your trip more enjoyable.
Knowing where you are, where you are going, how long it will take to get there etc. can be determined before you leave the dock.
You want to go here (DESTINATION)
You are here (START)
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54. Travel from Point A to Point B – “Easy? Right?”
Planning
Planning cont’d:
Looks easy – Don’t be to sure!
Travel from Point A to Point B – “Easy? Right?”
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55. Before you start – Check your Chart
Planning
Shallow Water
Planning cont’d:
Before you start any trip, a wise navigator will check a chart to be sure you can safely get to your destination.
Before you start – Check your Chart
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56. What’s in Your Way? Shallow Water >> Destination
Planning cont’d:
Hazards that may be unseen can be located on a chart and avoided before they become a problem for you.
start
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57. Selecting a Safe Path
The direct path goes over a shoal – plan a safer passage.
Planning cont’d:
Preplanning to give you options before you leave the dock.
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58. What is a Good Path?
A careful scan along the path from Start to Destination will indicate features that will bar safe passage.
Clearly, careful Planning and a current Chart are essential tools for a navigator.
Planning cont’d:
Every navigator wants to have the confidence of his passengers and himself that he will make the trip enjoyable and safe. Preplanning goes a long way in giving you the confidence you need. Preplanning also helps you handle the unexpected.
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59. Chart and GPS Position Accuracy
Chart Correction Date:
The older your Chart, the more differences between your Chart and reality!
Check Notices to Mariners (now on-line)
Position Accuracy cont’d:
Check Notices to Mariners often. and/or keep charts current.
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60. Chart Accuracy Environmental Factors:
Large storms or just the daily effects of wind, tide, et cetera, cause coastal areas to be in a constant state of change.
When in doubt, check the latest obtainable information and sources.
Position Accuracy cont’d:
Check local knowledge. The local mariners are the best source for recent changes to surrounding area dangers.
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61. Questions ? … Comments
Surely, you have questions.
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62. United States Power Squadrons ®
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