Disclaimer: my experience is in containerized cargo, not in bulk like LNG.
I take issue with your first paragraph. While it's true that many American flagged carriers run a mainland to island business (PR, Hawaii) I wouldn't call them specialized. Matson and APL are both very large US flagged carriers that have significant trans-pacific volume (i.e. the most significant, mainstream global tradelane). In fact, Matson (US flagged) has a reputation for being a premium transpac carrier because they operate their own dedicated terminals and can turn around cargo much faster than others.
None of this is to say that the Jones Act isn't a protectionist piece of garbage, but the situation isn't as dire as you lay out.
The Jones Act isn't really protectionist. We don't allow foreign registered trucks to carry cargo between American cities so why should the rule be any different for ships?
The Jones Act is highly protectionist, both in original intent and in actual effect. [0] The act grants a virtual monopoly on domestic island freight to the few US flagged carriers. You may have heard that things in Hawaii are expensive because "they have to ship everything there." That's true, but misleading. A gigantic share of US consumer goods are also shipped from China, but you don't hear similar complaints about the cost of goods in Tennessee . That's because the US carriers can literally charge anything they want [1].
Your analogy isn't accurate. The accurate analogy would be "We don't allow trucks manufactured outside the United States, owned and operated by non-US companies, and driven by non-citizens to carry cargo between American cities.
> A gigantic share of US consumer goods are also shipped from China, but you don't hear similar complaints about the cost of goods in Tennessee .
While I'm certain you are infinitely more knowledgeable on this than I am, this doesn't seem to be a fair comparison. Doesn't the scale difference (Hawaii vs the continental US) have an important impact on efficiencies and costs?
As a mere reader, if non-US-flagged ships aren't allowed to stop at two consecutive US ports, then it seems likely they'd head to California instead of Hawaii, since it is the larger market, leaving Hawaii, which would otherwise receive cheap cargo on a mid-way stop, instead having to them import it from the mainland, so paying shipping for both the initial foreign-to-mainland trip and then a low-competition and more expensive US-flagged mainland-to-Hawaii trip.
If they could stop at Hawaii before and then after mainland, then they could drop off containers when passing each way, lowering Hawaii's costs.
It certainly is; note that in the EU the single market rules allow trucks from any country to ship between and within other EU countries with a single permit.
The post Brexit arrangements for this remain unclear, which is why people are starting to stockpile.
Yes, carbotage laws apply to road and air traffic as well, albeit not as strict as the Jones Act.
A Canadian truck based in Windsor (driven by a driver with valid work visa) is allowed to pick up goods in Detroit before going to Buffalo, because this leg of the trip is considered incidental to an internatonal route. However if the truck were to make multiple return trips between Detroit and Buffalo it would not be legal
I take issue with your first paragraph. While it's true that many American flagged carriers run a mainland to island business (PR, Hawaii) I wouldn't call them specialized. Matson and APL are both very large US flagged carriers that have significant trans-pacific volume (i.e. the most significant, mainstream global tradelane). In fact, Matson (US flagged) has a reputation for being a premium transpac carrier because they operate their own dedicated terminals and can turn around cargo much faster than others.
None of this is to say that the Jones Act isn't a protectionist piece of garbage, but the situation isn't as dire as you lay out.