I would only like this idea if the whole aim was to increase rainfall in traditionally dry areas. Imagine a fleet of these ships being used to increase agriculture and human prosperity. Instead it will be used to reinforce the lie of Man Made climate change and will be used to actually alter the environment in order to reinforce their controlling ideals.
An interesting thing about some kinds of ocean algae is if they are bothered by too much UV radiation they emit a chemical that causes water vapor to condense into clouds, which then reduce the UV level. Saltwater algae somewhat regulate their local climate.
Making algae biodiesel in the open ocean could be used to make more freshwater and cool the climate. But the Saudi's are going to hate this particular idea because it would ruin their free ride.