The Jones act doesn't prohibit anything about bringing ships into the US to construct things. The closest reason I can think of you thinking that is it allows injured sailors to sue for damages. Maybe that equipment leads to a huge number of injuries?

The cabotage provision of Jones act says a foreign (built) vessel is not allowed to move stuff between two points within US waters https://www.law.cornell.edu/uscode/text/46/55102 . There's also actually a separate dredge act too (now here: https://www.law.cornell.edu/uscode/text/46/55109) .

So a crane like this one https://www.youtube.com/watch?v=yvicq-kvVbw ; it picks thing up and sets thing back down. In US waters? Verboten ("nee meneer, helaas verboden", in this case). Sure there's workarounds with barges sometimes; but it gets silly.

Or this rather large 'bulldozer' (a trailing suction hopper dredger) : https://www.youtube.com/watch?v=MhysyOJHY8A . Move mud from spot where it's unwanted to spot where it's needed. Operates in coastal/river areas. Fixes dunes, replenishes beaches, creates walls, places landfill; all at scale. Builds things like https://en.wikipedia.org/wiki/Palm_Islands, https://en.wikipedia.org/wiki/Kansai_International_Airport, https://en.wikipedia.org/wiki/Maasvlakte_2 .

Jones act and more specifically dredge act even: you're moving stuff inside US territorial waters.

Both cases it's not (or barely) made in the US, and you can't hire the big crews from elsewhere. There's no competition, and this has resulted in no incentive to learn, keep up or even try.

NB Heritage foundation on some of this: https://www.heritage.org/trade/commentary/113-year-old-law-h...