There are a few good reasons to repeal the Jones Act (reduce shipping and trade costs in Hawaii, Alaska, and Puerto Rico) and a lot of really bad ones (the domestic shipping industry will be completely killed, and you're inviting unbounded liability from unregulated, fly-by-night international actors who don't give two craps about our laws.)
The way ocean shipping currently works is entirely incompatible with any national rule of law. Flags of convenience and corporations with non-existent liability mean that nobody in the international industry is actually following any of the rules.
The domestic industry has to follow them, which is the reason why it's not cost competitive.
The problem stemming from flags of convenience is well known and the Port State Control system [1] was created to manage it.
In other words: live up to our requirements or we will detain your vessel.
The US is not a signatory to any international port state control scheme but as is usual the US runs its own nearly equivalent scheme through the coast guard. [2]
[1]: https://en.wikipedia.org/wiki/Port_state_control
[2]: https://www.dco.uscg.mil/Our-Organization/Assistant-Commanda...
The problem is that there is too much to check, too many incentives and reasons to break the rules, and too few consequences for people who do.