At 2126, you pass Morganza Bend Light (mile 278.4 AHP). At 0122, 4 January, you pass Red River Landing Gage (302.4 AHP). You have been turning for 7.5 mph. What is the current?
• Difference between speed through the water (what you are turning for) and speed made good over ground • Using distance = rate × time to find actual speed over ground between river miles • Relationship: Current = Speed over ground − Speed through the water (upbound vs. downbound)
• First, convert the time between the two mile marks into hours. What is the exact elapsed time between 2126 and 0122? • Next, find how many miles you traveled between Morganza Bend Light (278.4 AHP) and Red River Landing Gage (302.4 AHP). What is that distance? • Using your elapsed time and the distance, compute your actual speed over ground. Then compare it with your 7.5 mph through-the-water speed to determine the current, considering whether you were going upriver or downriver.
• Be sure you are using miles per hour (mph) and decimal hours, not minutes, when you compute speed. • Confirm whether river mile numbers are increasing or decreasing in the direction you traveled so you know if current is helping or opposing you. • Before choosing, check that your current value is a reasonable fraction of 7.5 mph, not larger than the vessel's through-the-water speed in this river situation.
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