🔍 Key Concepts

• Using a DR (dead reckoning) track and time-speed-distance relationship to predict sighting time • Converting distance off to time using your vessel's speed made good • Effect of exceptionally clear visibility on how far away you can see a light structure like a lighthouse or light tower

💭 Think About

• Given the vessel’s speed, how long before your calculated time of closest point of approach (CPA) would you first expect to see the light, if visibility lets you see it from its full nominal range? • How does using the maximum visible range of the light (from the Light List or chart) change the sighting time compared to using a shorter, more average visibility range? • Look at the difference in minutes between the possible answers: what does that suggest about how far away (in nautical miles) you might be when you first see the light, at your current speed?

✅ Before You Answer

• Confirm the speed in knots you are using for the DR problem and convert that to minutes per mile. • Check the charted or nominal range of Chesapeake Light and compare that to any assumed visibility in the problem statement. • Make sure you’re using the time when you are abeam or nearest the light as a reference, then count backwards using Time = Distance ÷ Speed to estimate the first sighting time.