Exactly as per the picture.
The Jones Act gives the yards, and the owners, a competition-free monopoly.
Therefore there is no need to compete and the owners are guaranteed an income no matter ho shabby or good the service.
Look at the discussion re the El Faro and El Yunque -nowhere else would elderly, uneconomic (Steam) vessels be employed commercially.
In WWII Henry Kaiser revolutionized US shipbuilding, since then, sadly, it has failed to develop of keep up with the times as the have a closed market.
Yes I understand the US seafarers fear of losing the act, but look at the decline it caused.
Globally there are regional trade networks:
Russia - Black Sea - Baltic - Volga Don Max vessels - Russia, Ukraine, ex Soviet states
Europe Med - Short sea freight, ro-ro, Kiel Canal max etc - Dutch, German, French, UK, Scandinavian owners
China - Internal rivers
North America - huge potential but the market must be free as it is in all trade areas.
The traditional towboats and sea barges are uneconomic whilst short sea vessels are far more efficient.
Look at the likes of Wagenborg: