🔍 Key Concepts

• Ship motions and axes: surge, sway, heave, roll, pitch, yaw • Difference between linear motions (along an axis) and rotational motions (about an axis) • Meaning of longitudinal, transverse, and vertical axes on a vessel

💭 Think About

• First decide: is heave a motion that moves the ship in a straight line, or one that rotates/tilts the ship? • Visualize the three main directions on a ship: front–back, side–side, and up–down. Along which of these does heave happen? • Match each ship motion name (surge, sway, heave) to one of the three straight-line directions; then pick the axis that describes that direction.

✅ Before You Answer

• Be clear which axis means up-and-down direction on a vessel • Separate in your mind motions along an axis (surge, sway, heave) from motions about an axis (roll, pitch, yaw) • Verify that the axis you choose correctly represents the vertical direction relative to the ship, not just its length or width