🔍 Key Concepts

• Dangerous semicircle and navigable semicircle of a hurricane in the Northern Hemisphere • How to draw relative motion vectors for your vessel and the hurricane • Using CPA (closest point of approach) ideas to maximize distance from a moving danger

💭 Think About

• Sketch the hurricane’s track (265°T at 25 knots) and your present position, then add your own possible tracks at 13 knots. Which general direction moves you away from the storm’s future positions, not just its present bearing? • Think about whether you want to pass ahead of, behind, or turn away from the hurricane’s track. In which case does your relative motion line from the hurricane to you lengthen the most over time? • Compare each answer’s course with the hurricane’s direction of movement. How does changing your course more northward vs. more westward affect your position relative to the storm’s right (dangerous) and left (navigable) semicircles?

✅ Before You Answer

• Confirm whether the hurricane’s bearing from you (120°T) places you initially on its right or left semicircle given its track of 265°T. • Check the relative speed between you and the hurricane: hurricane speed 25 knots vs. your 13 knots. How does this limit your options for crossing its track? • For each proposed course, imagine where you’ll be after several hours relative to the storm’s track line. Which course keeps increasing separation from that track rather than converging toward it?