Navigation Basics: Reading Charts and Using GPS

Navigation is the art and science of safely guiding your vessel from one point to another. While modern GPS technology has made navigation more accessible than ever, understanding the fundamentals of chart reading and traditional navigation techniques remains essential for safe sailing. As a former Coast Guard officer who has coordinated dozens of search and rescue operations, I can tell you that sailors who understand navigation basics are far less likely to find themselves in dangerous situations.

This comprehensive guide will teach you everything you need to know about marine navigation, from reading nautical charts to using GPS effectively, and why backup navigation skills could save your life when technology fails.

Understanding Nautical Charts

Nautical charts are far more than simple maps—they're complex documents containing crucial information about water depths, hazards, navigation aids, and coastal features. Learning to read charts properly is fundamental to safe navigation.

Chart Basics

Australian nautical charts are produced by the Australian Hydrographic Office and follow international standards. Each chart covers a specific geographic area and scale, with larger scale charts showing more detail for harbor and coastal navigation, while smaller scale charts cover broader ocean areas.

Charts use a system of symbols, abbreviations, and color coding to convey information efficiently. Water areas are typically shown in white or light blue, with deeper water in white and shallower areas in progressively darker blue. Land areas appear in buff or tan colors, with important coastal features clearly marked.

Depth Information

Depth is one of the most critical pieces of information on any nautical chart. Depths are shown as soundings—numbers indicating the depth of water at that specific location. In Australian waters, depths are typically shown in meters and relate to the chart datum, usually Lowest Astronomical Tide (LAT).

Depth contour lines connect areas of equal depth, making it easy to visualize the underwater topography. Pay special attention to the 2-meter, 5-meter, and 10-meter contour lines, as these are particularly relevant for yacht navigation.

Areas that dry at low tide are shown with a special symbol, and rocks that are always submerged but pose a hazard to navigation are clearly marked. Understanding these symbols could prevent a costly grounding or worse.

Navigation Aids

Charts show the precise locations and characteristics of navigation aids including lighthouses, buoys, beacons, and radio navigation facilities. Each aid has specific symbols and information about its light characteristics, colors, and operational status.

In Australia, the lateral buoyage system follows the IALA-A standard, where red buoys mark the port (left) side of channels when entering from seaward, and green buoys mark the starboard (right) side. Remember: "Red Right Returning" doesn't apply in Australia—it's "Red Left Returning."

Chart Plotting Fundamentals

Knowing how to plot courses and positions on a chart is essential for navigation planning and position monitoring. These skills become crucial when GPS fails or you need to verify electronic positions.

Position Plotting

Every position on a nautical chart can be precisely defined using latitude and longitude coordinates. Latitude lines run east-west and measure distance north or south of the equator. Longitude lines run north-south and measure distance east or west of the Prime Meridian.

To plot a position, find the intersection of the appropriate latitude and longitude lines on your chart. Practice this skill regularly, as being able to quickly plot positions is essential for emergency situations.

Course and Bearing Lines

A course is the direction you intend to travel, while a bearing is the direction from your position to another object or location. Both are measured in degrees from 000° to 359°, with 000° representing true north.

When plotting courses on a chart, use parallel rulers or a course plotter to ensure your lines are accurately drawn. Always work with true bearings on the chart, then convert to magnetic bearings for compass use by applying the local magnetic variation.

Distance Measurement

Charts include distance scales, but you can also use the latitude scale on the side of the chart to measure distances. One minute of latitude equals one nautical mile, making it easy to measure distances using dividers or a compass.

Remember that longitude spacing varies with latitude, so only use the latitude scale for distance measurement, never the longitude scale.

GPS Navigation

Global Positioning System (GPS) technology has revolutionized marine navigation, providing accurate position information anywhere on Earth. However, understanding how GPS works and its limitations is crucial for safe navigation.

How GPS Works

GPS uses a constellation of satellites orbiting Earth to provide position information. Your GPS receiver calculates its position by measuring the time it takes for signals to travel from multiple satellites. The more satellites your receiver can "see," the more accurate your position will be.

Modern GPS receivers typically provide accuracy within 3-5 meters under normal conditions, which is more than adequate for most marine navigation needs. However, accuracy can be degraded by atmospheric conditions, satellite geometry, or intentional interference.

Chart Datums and GPS

One crucial concept that many sailors misunderstand is chart datum. Your GPS provides positions based on WGS84 datum, while older charts may use different local datums. Using the wrong datum can result in position errors of hundreds of meters.

Modern Australian charts are based on GDA94, which is essentially identical to WGS84 for navigation purposes. However, always check your chart's datum information and ensure your GPS is set to match.

Waypoint Navigation

GPS allows you to navigate between predetermined waypoints—specific positions you want to visit or pass through. Effective waypoint navigation requires careful planning and regular monitoring to ensure you stay on track.

When creating waypoints, choose positions that provide safe water and adequate clearance from hazards. Plan your routes during daylight hours when you can carefully study charts and identify potential problems.

Traditional Navigation Techniques

While GPS is remarkably reliable, understanding traditional navigation techniques provides essential backup capabilities and helps you understand the principles underlying all navigation.

Dead Reckoning

Dead reckoning involves calculating your current position based on your previous known position, course steered, speed, and elapsed time. While simple in concept, dead reckoning requires careful attention to detail and regular position updates.

To practice dead reckoning, start from a known position and carefully log your course, speed, and time. Plot your estimated position on the chart and compare it with GPS readings to understand the accuracy of your calculations.

Factors that affect dead reckoning accuracy include current, leeway (sideways movement caused by wind), and steering errors. Experience helps you estimate these factors and improve your dead reckoning accuracy.

Visual Bearings

Taking visual bearings to known landmarks provides an excellent way to determine your position and cross-check GPS readings. To take a bearing, use a hand-bearing compass to measure the direction from your position to a visible landmark.

Two bearings create a position line, and three or more bearings provide a position fix. The more accurate your bearings and the better the angle between them, the more precise your position fix will be.

Practice taking bearings in familiar waters where you can verify your results. This skill becomes invaluable when GPS fails or you need to verify your electronic position.

Depth Contour Navigation

Your depth sounder provides valuable navigation information beyond simple safety monitoring. Following depth contours can help confirm your position and provide guidance when visibility is poor.

By comparing depth readings with chart soundings, you can often determine your approximate position or confirm you're on the correct track. This technique is particularly useful in areas with distinctive underwater topography.

Compass Navigation

The magnetic compass remains the most reliable navigation instrument on your boat. Understanding compass errors and how to use your compass effectively is essential for safe navigation.

Magnetic Variation

Magnetic north and true north are not the same direction. The difference between them is called magnetic variation, which varies by geographic location and changes slowly over time. Australian charts show the local magnetic variation and its annual rate of change.

When working with chart bearings and courses, always apply magnetic variation correctly. The memory aid "Easterly variation, compass best" means that with easterly variation, magnetic bearings are greater than true bearings.

Compass Deviation

Deviation is the error in your boat's compass caused by magnetic influences aboard your vessel—engines, electronics, metal fittings, and other magnetic materials. Unlike variation, deviation changes with your boat's heading.

Professional compass adjustment can minimize deviation, but some will always remain. Create a deviation table for your boat by comparing compass headings with known bearings on various courses.

Steering Compass vs. Hand-Bearing Compass

Your main steering compass is used for maintaining course while sailing or motoring. A hand-bearing compass is a separate instrument used for taking bearings to landmarks and navigation aids.

Hand-bearing compasses should be used away from magnetic influences, typically at the bow or stern rail. Practice using your hand-bearing compass until you can quickly and accurately take bearings to visible landmarks.

Electronic Chart Systems

Electronic chart systems combine digital charts with GPS positioning to provide real-time navigation displays. These systems offer significant advantages but also require understanding to use safely.

Types of Electronic Charts

Raster Charts: Digital photographs of paper charts that look identical to their paper counterparts. Easy to interpret if you understand paper charts, but they can't be enhanced with additional electronic features.

Vector Charts: Charts created specifically for electronic display, allowing features to be turned on/off and providing additional functionality like automatic course calculations and collision avoidance.

Chart Updates

Electronic charts must be kept current just like paper charts. Navigation hazards, aid changes, and new construction can make outdated charts dangerous to use.

Establish a regular update schedule for your electronic charts and always check Notices to Mariners for critical updates that might affect your planned routes.

Backup Systems

Electronic systems can fail, so always maintain backup navigation capabilities. This might include paper charts for your sailing area, a handheld GPS, and traditional navigation instruments.

Practice using your backup systems regularly so you're prepared when primary systems fail. Murphy's Law suggests that electronics will fail at the worst possible moment.

Navigation Planning

Proper navigation planning is essential for safe and efficient passage making. Good planning prevents problems and helps you respond effectively when situations change.

Passage Planning Process

Start by studying charts of your entire route, identifying hazards, safe harbors, and critical navigation points. Consider weather, tides, and your boat's capabilities when planning your route and timing.

Create a detailed plan including waypoints, courses, distances, and estimated times. Identify abort options and alternative destinations in case conditions change during your passage.

Pre-departure Checks

Before departing, verify that all navigation equipment is working properly. Check GPS accuracy against known positions, ensure charts are current, and confirm that backup systems are operational.

Brief your crew on the planned route, key navigation points, and emergency procedures. Everyone aboard should understand the basic navigation plan and know how to use emergency equipment.

Monitoring Progress

During your passage, regularly check your position and progress against your plan. Plot your position at regular intervals and compare actual progress with planned progress.

Be prepared to modify your plan if conditions change. Safe navigation requires flexibility and good judgment, not blind adherence to a predetermined plan.

Navigation in Poor Visibility

Fog, rain, and darkness create special navigation challenges that require additional skills and preparation. Understanding how to navigate safely in poor visibility could prevent a serious accident.

Radar Navigation

Radar provides invaluable information for navigation in poor visibility, allowing you to see land, other vessels, and navigation aids that aren't visible to the eye.

Learn to interpret radar displays and understand how different objects appear on radar. Practice radar navigation in good visibility so you understand what you're seeing when visibility is poor.

Sound Signals

Sound signals help you navigate and avoid collisions in fog. Learn the required sound signals for your vessel and listen carefully for signals from other boats, fog signals from navigation aids, and sounds that might indicate hazards.

Reduced Speed Navigation

Always reduce speed in poor visibility to give yourself more time to react to hazards. Use your depth sounder actively to help confirm your position and detect shallow water.

Post extra lookouts and ensure everyone aboard understands their responsibilities during reduced visibility navigation.

Emergency Navigation

When navigation equipment fails or you become disoriented, basic emergency navigation skills can help you reach safety.

When GPS Fails

If your GPS fails, immediately begin dead reckoning from your last known position. Use visual bearings, depth contours, and any other available information to establish your position.

Consider using your mobile phone's GPS as a backup, but remember that marine GPS units are typically more accurate and reliable than phone GPS.

Improvised Navigation

If you lose your compass, you can determine approximate direction using the sun, stars, or other natural indicators. While not precise, these techniques can help you maintain a general sense of direction until you reach help.

The sun rises in the east and sets in the west, providing rough directional information. At night, the Southern Cross points toward the south celestial pole, giving you an approximate south bearing.

Navigation Rules and Regulations

Understanding navigation rules and regulations is essential for safe boat operation and helps prevent collisions and groundings.

Right of Way Rules

Navigation rules establish which vessel has right of way in various situations. Understanding and following these rules prevents collisions and ensures orderly traffic flow in busy waters.

Power vessels generally give way to sailing vessels, but sailing vessels must give way to vessels engaged in fishing, restricted in their ability to maneuver, or not under command.

Speed Regulations

Speed limits apply in many harbors, bays, and restricted waters. Always comply with posted speed limits and reduce speed in congested areas, even when no specific limit is posted.

The fundamental rule is to operate at a safe speed for conditions, which may be well below any posted limit when visibility, traffic, or other factors create hazardous conditions.

Conclusion

Navigation is a fundamental skill that every sailor must master for safe boat operation. While modern GPS technology has simplified many aspects of navigation, understanding the principles behind navigation and maintaining traditional skills provides essential backup capabilities.

Start by mastering chart reading and basic plotting techniques, then gradually build your skills with electronic systems and advanced techniques. Practice regularly in familiar waters where you can verify your results and build confidence in your abilities.

Remember that navigation is as much about planning and preparation as it is about technical skills. Good navigation habits, regular position checking, and maintaining backup systems will serve you well throughout your sailing career.

Most importantly, never hesitate to ask for help or clarification when you're unsure about navigation procedures. At Tip Frontier, we emphasize navigation skills in all our advanced courses because we know that confident navigators are safe sailors.