Sodium batteries have substantially reduced thermal runaway risk compared to lithium. Worst case, the ship sinks during a fire and the batteries are flooded. Charging infra is likely similar to existing EV ferry charging infra. Ship pulls into the berth and starts soaking the battery storage up to 1C up until departure. Could probably use a heat exchange and raw water available for battery cooling to maximize charge current curve, actively cooling the battery storage during charging.

https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2023-04/...

https://old.reddit.com/r/electricvehicles/comments/1m8wlou/e...

No need do charge in-situ, the ships (and ports) already transfer several times the battery volume and weight on berthing quickly . The battery systems could be designed to leverage that .

Fire hazards are there for any fuel, Safety systems evolve to handle them. The environmental impact would be more localized than an oil spill.

A quick googling suggests that unloading such a vessel takes at least a couple of days, more likely 3-4.

Assuming two days available to charge the vessel, you'd need about 100MW continuous. Not trivial, but doable.

As far as battery fires go, sure, but a) there are already a lot of electric ferries in service so designing safe maritime battery packs isn't a new challenge and b) the alternative isn't exactly risk free either; we've seen plenty of oil spills from ships.