CHARTS & MAPS

An Introduction

Guiding Principle

Understanding maps and charts, their symbols and notation, and their applied uses, is a fundamental base for good seamanship and interpreting the marine environment.

Performance Objectives

• Students should be able to:
• Identify chart and map types.
• Recognize chart symbols and know how to find ones they don’t recognize.
• Understand the importance of chart symbols and notation for applied seamanship.
• Identify several methods of preparing charts for trips.

Materials

• Topographic Maps
• Nautical Charts of different scale
• Waterproof Charts
• Laminated Charts
• Chart case
• Chart book of Eastern seaboard
• Computer Software and Online Resources
• Chart No. 1

Content

Maps and Charts are representations of earth from a bird’s eye view.  Maps concentrate on land features; charts concentrate on sea features.  Both have practical uses for sea kayakers depending on the nature of the journey and the environment.  The many islands, submerged ledges, extensive intertidal zones, and aids to navigation make charts a common choice for the Maine coast.

Scale 

A map or chart’s scale refers to the distances that they represent.  They are presented as a ratio 1:20,000 or 1:40,000 is a common ratio for charts used by kayakers while 1:100,000 would cover a much larger area.   The charts below represent Peaks Island at two different scales.  The chart on the left would provide more uses while afloat for keeping track of exact location.  The chart on the right would be useful for planning a multi-day trip.

Latitude and Longitude

• Latitude and Longitude provide a way to slice up the earth so that exact location can be determined.
• Latitude and Longitude of the boathouse on Peaks Island:
• Latitude = 43o 39’ 25” N, Longitude = 70o 11’ 55” W (read seventy degrees, eleven minutes, fifty five seconds West).
• Rarely used piloting but useful for those who navigate with GPS.

Finding Distance and Speed

• Distances on the sea are generally in nautical miles (nm)
• 1 minute of latitude (marked on the side of the chart) = 1 nautical mile ~ 6,080 ft
• 1 nautical mile = 1.15 land miles
• Paddler can use dividers, fingers, or a length of string to determine the distance between two points.
• 1 nautical mile per hour = 1 knot (kn)
• A group of fairly competent paddlers in light sea conditions can travel at aproximately 3 knots, but this varies significantly depending on group and conditions.

Symbols and Notation

• Some symbols for common hazards and/or obstructions:
• Aids to Navigation, natural features, anomalies and hazards– all have unique notation.
• The level of detail can be high and symbols can be esoteric - even for veterans.
• Paddlers can refer to NOAA Chart 1 for a complete index of symbols and notation.

Chart Datum, Depths, and Drying Heights

Depths on the chart are generally taken at Mean Lower Low Water (MLLW), or the mean of the lower low water heights over a 19 year period. This is known as chart datum. Specific underwater obstructions sometimes have a number associated with them and which can mean different things depending on the notation.

The Compass Rose

Compass roses are located at several locations on charts.  These are valuable for:

• Plotting a course.
• Finding a bearing to a landmark.
• Finding the variation between true North and magnetic North.

Preparation for Sea Kayaking

Charts are the wrong shape to put on the deck of the kayak, so the paddler has several options:

• Color photocopy the desired sections of the chart and laminate the photocopy.  Be sure to include a scale for distance and a compass rose on the photocopy.
• Use charts made from waterproof paper and fold to the correct size.
• Fold charts and carry in a “waterproof” chart case.

Where to Purchase

Printed topographical maps are available from many reputable outdoor stores. Printed charts may be purchased from marine supply stores. Online maps and charts can be downloaded and printed. Chart software that combines tide and current information is also available. This software can now be used in conjunction with modern GPS.

Tasks & Activities

• Have paddlers determine distance from one point to another.
• Have paddlers compare and contrast features on a nautical chart with a topographical map.
• Find the lat/long of a point.
• Divide up symbols on a map/chart and have paddlers find what those symbols mean and share with the rest of the class.

Assessment Tools

• Paddlers should show knowledge of advantages and disadvantages of maps and charts.
• Paddlers should demonstrate knowledge of chart symbols and notation.
• Paddlers should prepare charts and place on their deck in the appropriate way.

Resources

MapServer - open source web mapping

Fundamentals of Kayak Navigation, David Burch.

Sea Kayak Navigation, Franco Ferrero.

The Practical Pilot, Leonard Eyges.