The ESA (Sentinel) data is somewhat delayed and has a low revisit period (AFAIK 6 days, although you might get lucky and get more due to overlap the further away from the equator you get) and low resolution. The Sentinel-1 data (SAR, synthetic aperture radar) might be somewhat useful for this as ships should be more easily identifiable on it and you don't have to worry about cloud cover, but probably still less useful than the delayed crossing data.

Ships don't move that quickly; AIS data refreshed once every few hours would probably be more than good enough.