Try this "Mechanisms of lightning formation in deep maritime clouds and hurricanes" [1] It suggests "that the formation of lightning in maritime clouds requires two conditions to be satisfied: a) significant vertical velocities and a large cloud-depth, and b) the existence of small aerosols with the radii lower than about 0.05 μ m in diameter in the cloud condensational nuclei (CCN) size spectra." The pollution from the ships in the form of sulphate will likely provide such small aerosols so then you just need to significant vertical velocities.

[1] - https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...