As I understand it, Hawaii had environmental concerns with ferries (requiring a review that was never completed), specifically whale/ship strikes and the risk of car-carrying ferries transporting invasive species between the islands. [1] I'm unsure if other islands would have similar concerns about cargo ships or not or if the environmental review would have been satisfactory if they'd just done it on time.
I'd expect ferries and/or small cargo ships to be an attractive option if allowed.
I'd expect ferries and/or small cargo ships to be an attractive option if allowed.
[1] https://en.wikipedia.org/wiki/Hawaii_Superferry