The largest dredgers in the world were built by a Spanish company, Construcciones Navales del Norte (CNdN), but the company has apparently been dissolved as of a few years ago. This source claims they had sub-250 employees. Their shipyard was purchased last year by an industrial real estate firm.
So here's an idea. The US-based Manson Construction Co., is currently building a 15,000 cubic yard dredger which will be the biggest in the USA. It's about 25% the size of the biggest dredgers. They hire some of the former employees from CNdN, so that they can get green cards. This gives MCC the expertise to build even bigger dredgers. It's an employee-owned company, so it can't be purchased outright and made to do this, but perhaps they can be convinced by the prospect of a big dredger commission?
Another large dredger, the Vasco da Gama, has about 80% of the capacity of the record-setting Leif Eiriksson and cost around $120 million. So if we use that as a ballpark, perhaps we can get a world-class dredger built in America for around $200 million?
One interesting aspect of this is that it's currently hard to understand what the Foreign Dredge Act of 1906 actually says. At the time of this writing, Wikipedia has no page for it.
When it comes to byzantine regulations like this, simply having better documentation might be useful for moving the regulation in a more sensible way.
AFAIK this is basically a nothingburger, but a bill to repeal the Foreign Dredge Act was introduced in December by Sen. Lee of Utah.
Be aware that the American Bureau of Shipping (ABS) will need to classify the vessel, and if they have not done so for a dredge of the size described for some time then it can be expected that this will add to a time estimate for completion.
The physics is not hard and the United States Army Corps of Engineers (USACE) manuals are good enough that they are used in various countries to educate young engineer's on coastal soil dynamics (Hi!), so if discussions of green cards are on the table then the right people within the US are being overlooked.
ABS certified steel is manufactured in America (of course but worth noting).
Manufacturing huge ships is a labour intensive operation and the bottleneck I suspect will be cost of Labor. Keppel Fels or Jurong can build comparable vessels for the likes of Valaris (the DPS-1 ne Atwood Condor is a Singapore build which is in my neighbourhood now) for peanuts because they employ thousands on thousands of serfs. Constructing a similar sized vessel with mechanical systems integrated in America would require a bypassing labour by investing hugely in automated fabrication plant and methods, on a large plot of land near a large port.
I expect Elon Musk could do it. Make the dredging company a subsidiary of the boring company and buy a plot of industrial portside land and build a marine giga-factory. Maybe Bezos will feel competitive enough to do it first.
A dollar-value answer doesn't quite address the question of whether the correct way to answer "we can do it" is by spending a fortune on American labour (seems like a good thing, pays mortgages) or a fortune on new and likely novel large scale autated fabrication processes (also seems like a good thing, pays different people's mortgages and possibly adds to current state of human knowledge and industry).
I'm doing some research into questions surrounding the Foreign Dredge Act of 1906, and thought I'd experiment by throwing this out there.
For context, the 31 biggest dredging vessels were not built in America, and thus cannot be used in America by law. We only have a small number of less capable vessels, and they often get redirected to short-term emergency tasks. This is preventing us from doing a bunch of very valuable things, like repairing or expanding ports, which end up taking much more time and money or not happening at all.
This podcast is recommended. You can find a transcript here. They claim that there's no way America will be able to have such capacity for at least decades. I want to verify that (and also check if any other claims here don't ring true)?
As an alternative to repealing the Dredge Act (which I'm exploring and planning to write about) another alternate would be to build world-class dredging vehicles here in America, such that they could be used. Before assuming that this is impossible, and to have a straight answer, what would happen if someone with deep pockets tried to commission a world-class dredging ship that would qualify? Could be done? Are there other impossible barriers to solve? How much would it cost and how much more would that be than building it elsewhere? How long would it take?