As you pass under the Greenville Highway Bridge, you estimate the current as 3.5 mph. What is the speed over the ground, if your vessel is making turns for 9 mph?
• Relationship between speed through the water and speed over the ground in a following or opposing current • How to add or subtract current from vessel speed depending on current direction • Unit consistency: both speeds given in mph so no conversion needed
• Is the current helping you (pushing from behind) or opposing you (coming from ahead) as you pass under the bridge? • In that situation, should the speed over the ground be greater than or less than the speed you are making through the water? • Which math operation (addition or subtraction) correctly represents the effect of that current on your vessel’s progress over the bottom?
• Confirm which way the current is flowing relative to your course before deciding to add or subtract • Check that you are using speed through the water (9 mph) and current speed (3.5 mph) in the same units • After you calculate, verify that your answer is reasonable: does it match what you expect for a vessel being helped or hindered by the current?
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