Shade cloth above the waves will facilitate evaporation

Without nets:
Often the wind blows almost saturated air along the surface of the sea. Because the air is almost saturated not much evaporation occurs into the air. The spray is blown along with the wind - the wind does not blow over the spray and the velocity of the wind relative to the spray is small because they are travelling at about the same speed. So there is not much evaporation of the spray. Also, the spray falls to the sea surface fairly quickly if the droplets are large and then little evaporation occurs.
With nets:
The spray will be caught in the coarse sail cloth nets. The wind will blow through the stationary nets and the wind will therefore have a high speed relative to the wet nets (the water is not blowing along with the wind) and this will facilitate evaporation.
The nets will hold water above the sea surface for a long time, enhancing evaporation.
The nets will provide a large wet surface, with air that is drier than the air being blown along the sea surface, blowing through them, enhancing evaporation,
The nets will be heated in the sun, enhancing evaporation.
Air pressure will build up at the nets and spray will be lifted over the top of the nets, increasing spray area.
Wind speed at the height of the nets will be greater than the wind speed at the surface of the sea, enhancing evaporation.
NOTE: With sea and land breezes the same air tends to move back and forth from land to sea and sea to land. So air could be blown back and forth through the wet nets and humidification could increase every day with each blowing of air through the wet nets. See https://pdfs.semanticscholar.org/4756/b65ef5715dc4bf4ce1b9ab4287c0fbe89cbb.pdf