Seminar Series 1 Welcome How to Use a Chart Presented by United States Power Squadrons ® All Maps...
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Transcript of Seminar Series 1 Welcome How to Use a Chart Presented by United States Power Squadrons ® All Maps...
Seminar Series
1
Welcome
How to Use a Chart
Presented by United States Power Squadrons®
All Maps and Charts courtesy of MapTech
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Seminar Series
2
Welcome
I am Harry Hebb, SNAlso Ron Swope, SN
Presented by United States Power Squadrons®
All Maps and Charts courtesy of MapTech
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Seminar Series
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How to Use a Chart
This Seminar is intended to serve as an introduction to basic chart symbols and use.
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Chart Symbols Chart References Compass Rose Locating a position
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Sources of Charts
Hydrographic Offices- U.S. – NOAA – NOS - U.K. – British Admiralty Charts- other…
Commercial- Maptech- Richardson’s- other…
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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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White
Blue
Green
Gold
Magenta
Colors Used on Charts
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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Chart Information
Horizontal (position) Datum
Source Chart
Correction Date
Depth Units
Chart Scale
Mileage Scale
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NM = 6,076.1155 ft
WGS .. World Geodetic System
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Chart Features
Compass Rose
Variation Reference
AnnualChange
MagneticScale
True North
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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
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Depths
Depth Soundingsat true position
[vertical numbers]
Drying heights above chart datum (green)[number is underlined]
Least depth inNarrow channel[number in parentheses]
No bottomat depth shown
SOUNDINGS
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Depths
Limit of dredged channel
Unsurveyedor inadequately
surveyed area
Depth & year of latest control survey
FAIRWAYS, AREAS
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Nature of the Seabed
Stones, gravel or shingle
Green: area that covers and uncovers
Rocky area
Coral reef
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Navigation Aid Symbols
Chart vs.
Reality
The object as it appears on the water is shown to the left of its symbol
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Finding Your Wayby using Piloting
Piloting typically refers to navigation by using land based objects as opposed to
celestial bodies.
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True versus Magnetic
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’
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True versus Magnetic
T … true
V … variation
M … magnetic
D … deviation
C … compass
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True versus Magnetic
T … true
V … variation
M … magnetic
D … deviation
C … compass
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True Virgins Make Dull Company … Add Whiskey
+ W or – E … from True to Comp
- W or + E … from Comp to True
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Selecting a Safe Path
The direct path goes over a shoal – plan a safer passage.
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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.
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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)
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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.
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