For the continental US, it forces frieght to rail and road. Rail and road work pretty well, but some elsewhere in the thread says rail and road cost a lot more than ocean shipping. I'm sure that only works for some goods, and some routes; rail and road shipping would continue to be in high demand. We also have some navigable rivers that could be used for more freight, but probably not big container ships, so I don't know that repealing the Jones act helps there.

But for Hawaii and Puerto Rico, it's a much bigger deal. Their access to goods made in the US is highly restricted, because the US shipping fleet is so limited. In theory, the Jones act would support US shipbuilding and US ship operation by providing a profitable domestic market, and these US operators could use those profits to help them compete in the world market for shipping. What has happened instead is US ship operations are so uncompetitive that they only operate in the Jones act space, and there's not enough business there to justify building ships that are comparable with international standards.

What I'm trying to say is if the US had a fleet of Panamax container ships, even if that fleet was a small part of the global fleet, they would regularly go between US ports on their voyages (as international ships do) and they would be able to take US bound cargos at costs comparable to international cargo; although probably with some markup because not every cargo ship can take it.

But there are no US Panamax ships, because they're not competitive internationally, and there's not enough demand that it makes sense to build a large enough shipyard to build them.

The same thing applies to the two other major classes of ocean shipping; tankers, and roll-on/roll-off car ships.

Shipping these goods with smaller vessels means more costs for everything and makes island living much more expensive. Disaster recovery in Puerto Rico is also frequently delayed by the Jones act, although limited time exceptions are often made.