How to calculate rate and direction aka drift and set
In the USA, the terms “set and drift” are often used when it comes to specifying current flow. It is found that this is confusing to many students and in the rest of the world the terms rate and direction are used. At NauticEd, we adopt the term “rate and direction” in favor of the student.
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RATE AND DIRECTION
Rate is the flow rate or speed of the current in knots aka “drift” in the USA
Direction is the direction the current is flowing towards expressed in True degrees aka “set” in the USA
Here is a simple problem to calculate Rate and Direction based on how a vessel went off course over a period of time.
Print out the PDF provided below or if you are a NauticEd Coastal Navigation student you can use your Chart 12354.
Question:
Your motor vessel has cleared out of the Channel and an electronic GPS fix at 1020 places your position east of the mark G “1” Fl G 2.5s at 41 deg 9.4 min N and 73 deg 5min E. You are making way at 5 knots towards the safe water mark RW “NH” approx SSE of the outer channel marks from at New Haven. At 1120 you take another electronic fix and you find your position to be 41 deg 12.7 min N and 72 deg 58 min W. What is the rate and direction of the current?
You’ll need a set of dividers and a protractor and a calculator.
Click to download
Answer:
Before you look ahead to the answer, give it a go – it’s actually pretty easy.
Download the PDF answer plot.
Next Question:
What course would you now steer to go to the safe water mark RW “NH”?
Answer to be posted April 30th 2015. Please give it a go and post your answer to our facebook page under the existing post “Calculate Course to Steer”
If you need help, consider taking our Coastal Navigation online class or our iPad eBook App Coastal Navigation course
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