You alter course to make good 076°T from your 2200 fix, and estimate you will make 13.6 knots over the ground. If the visibility is 5.5 miles, what is the earliest time you will sight Falkner Island Light? (nominal range 13 miles)
• Geographic range vs. nominal range of a light and how visibility limits what you can actually see • Using speed-time-distance: how far you travel in a given number of minutes at 13.6 knots • Converting the visible range (in miles) into time to travel at your speed over the ground
• First, decide what limits when you will see the light: is it the nominal range, the geographic (visible) range from your height of eye and the light’s height, or the 5.5-mile visibility? • From your 2200 fix, think about how many miles from Falkner Island Light you must be before you can actually see it, given the 5.5-mile visibility and the light’s listed ranges. • Once you know that distance, compute how long it takes to cover that distance at 13.6 knots, then add that time to 2200 and compare to the answer choices.
• Confirm which range value (nominal 13 miles vs. actual visible range with 5.5-mile visibility) you should use to determine first sighting distance. • Carefully convert knots to NM per minute (13.6 knots ÷ 60) before finding the time in minutes. • Make sure you are using the distance from your 2200 fix to the light minus the distance at which it becomes visible, not the full distance to the light.
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