This strange pattern at sea is what happens when two wave systems cross each other at nearly perpendicular angles. This can occur when waves generated by one weather system collides with waves generated by another weather system, usually at a place that is far away from both weather systems.
Even on the calmest days, storms raging elsewhere on the ocean create rolling waves that radiate away from the storm and washes the shore of distant land. These are called swells. When two swells coming from two different directions collide, we get 'cross sea,' which is what is happening in this picture.