Energy moves across the sea surface in visible form. A wave is a disturbance that travels through the water, transferring energy while the water particles themselves mainly oscillate in place.

Wind-generated waves dominate everyday seafaring. Their height, length, and period depend on wind speed, duration, and fetch. Waves affect ship motions—pitch, roll, and heave—and can damage structure and cargo if severe. Breaking waves on the deck are a serious hazard to people and equipment.

Navigators and masters choose speed and course to reduce the worst motions. Wave forecasts are a standard part of marine weather information. Understanding the difference between sea and swell helps in anticipating how the ship will behave.

• Surface disturbance that transfers energy across water
• Primarily generated by wind
• Affects ship motion and deck safety
• Described by height, length, and period