🔍 Key Concepts
• Six degrees of freedom of ship motion: surge, sway, heave, roll, pitch, yaw
• Difference between rotational motions (about an axis) and translational motions (along an axis)
• Meaning of transverse stability: stability side-to-side (athwartship), not fore-and-aft
💭 Think About
• From the illustration, identify which axis is called the longitudinal axis and which way the ship moves or rotates when that motion occurs
• Ask yourself: transverse stability is the ship’s resistance to heeling over sideways—does that relate more to a sideways rotation, or to a straight-line sliding motion?
• Look at which motion in the diagram clearly shows the ship rotating side-to-side about its longitudinal axis
✅ Before You Answer
• Be sure you can distinguish motion along an axis (surge, sway, heave) from motion about an axis (roll, pitch, yaw) using the arrows in the figure
• Confirm which axis is transverse (athwartship) and which motion changes trim fore-and-aft versus side-to-side stability
• Before choosing, verify: which motion would be excited most if the ship were hit by a beam sea affecting its athwartship stability?