It’s not cutting-edge, technologically speaking, but still a pretty sizeable engineering project.
I have heard of a few temporary dry docks that were used to good effect. When Boston was building the Big Dig, it required making a tunnel under Fort Point Channel. Ordinarily, the tunnel sections would be built in a shipyard and floated into position, but there were low bridges over the channel. The construction team dug a huge casting basin, and built the tunnel there. I heard it’s the most expensive section of highway ever built.
Similarly, when Washington was replacing one of the floating bridges over the lake just east of Seattle, a temporary construction site was created on the coast, and bridge segments brought to the lake by tugboats. Size was limited by locks.
One other complexity with drydocks: Ships are designed to be supported by their entire sub-waterline surface simultaneously. Obviously that’s not strictly necessary, and you have some margin to get away with a more concentrated force, but to support a ship with solid supports, you still need supports on a decent fraction of the ship’s surface area. And if you want your drydock to be able to service more than one model of ship, those many supports all need some sort of articulation. Lots of supports that can be articulated and support a lot of weight is an engineering challenge, and it’s an even bigger engineering challenge for a drydock that can handle larger ships.
Most civilian ships are drydocked in Asia where labour is cheaper. And this has been going on so long that now not only is the labour cheaper, it’s more skilled.
I guess you can use “articulation” to describe a bunch of lumps of concrete and wood of varying heights and sizes that you move around to appropriate positions. But it seems a fancy term for what remains a very simple solution.
A dry dock is not just the facility, it requires a large skilled labor force and hopefully, an experienced management team. The U.S. ship building/repairing industry has been declining for decades, as noted above, much of that business moved to Asia.
And that you can move around into position around a ship that’s almost filling up the space, underwater. You can’t empty out the water until the supports are in place.
Every dry dock image I’ve ever seen of a warship is supported by wood propping it up. In the case of this image of the Nimitz, it’s pretty flat on the bottom, so there’s not even really much stacking necessary.
ETA in other images, it seems those might be concrete blocks it’s stacked on. Either way, not much in the way of articulation.
The keel blocks are moved into place manually using cranes and fork trucks per the hull plan while the dock is drained, then the dock is flooded and the ship is towed in. Some minor amount of shimming can be done by divers to ensure consistent contact, and lateral supports are added while the dock is drained to keep the ship aligned but all of the hull supports have to be moved into place when the dock is evacuated.. There isn’t any kind of self-articulating system that automagically forms to the hull.
As the link by @TokyoBayer illustrates, a dry dock is a massive civil engineering structure requiring enormous resources and power to operate. Describing it as “… a big hole in the ground with a door and water pumps,” is like describing the Hoover Dam as a big wall of concrete. And as @motu notes, a dry dock facility isn’t just the structure but all of the equipment, infrastructure, and skilled labor and expertise that makes it work. Bomb or otherwise disrupt that and your dry dock is nonfunctional until you can repair and restaff the facility.
I always assumed that the supports in a dry dock were put in place before the ship even comes in. Pump all the water out, use a crane to swing blocks (concrete, wood, or whatever) into place, let the water back in, and sail the ship into place.
That relies on a few assumptions. You have to know the shape of the hull, some means of measuring locations withing the dock, and then position the ship and hold it in place as the water gets pumped out and the ship settles onto the supports.
Does anyone know if that’s how it’s done? I have someone I could ask.
I’m a federal contractor who recently started supporting USN SSP, and one of my training/orientation courses included images of a drydock with an SSBN in it – and some people, for scale. I was blown away by even just that! I’d love to get to GA/WA someday and see the facilities and a boat in person. I’m sure my head would hurt for days afterwards…in a good way.
Heh, be careful what you wish for. I’ve worked on boats for about 25 years (5 active-duty, 20 as an engineer) and I spent my first few years in the industry on the road and on boats at least 75% of the time. It gets old fast and I’d be fine never seeing a boat again haha.
(Of course, it doesn’t help that having to go to a boat generally meant something was broken.)
In my experience, something is always broken on a boat. If there isn’t anything that seems broken it is just because you haven’t found it yet, and are likely to discover it at the most inconvenient time.
They say that “The two happiest days in a boat owners life are the day they buy the boat, and the day that they sell it.” Now imagine that that magnified by a price tag of several billion dollars.
This. It’s a significant bit of engineering that needs to be maintained. It’s basically a displaced Panama Canal lock with a large scale factory surrounding it.
For repair work there is the option to use a floating dry dock which can be moved as needed.
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