Waves are caused when air moves across water. This could be because the wind moves above water or because tides move water under the air (or both!) The larger the distance this takes place over and the more movement from the tide or wind, the larger the waves. When waves crash into a ship, the coast or even each other, they make sounds.
Listen to intensity of the waves.
What do the sounds tell you about the weather?
Can you work out what the waves are crashing onto – how can you tell this?