[teebs]

As others say, it's about the size of the port. But it's not only that those ports can't handle more ships - it's also that many of the ships in operation are so big they can't fit in smaller ports. I know that Oakland, for example, is always going to be second tier because it's just not possible to send the largest container ships into the San Francisco Bay without rebuilding a lot of the port to handle much bigger ships - dredging, larger cranes, larger docks.

This phenomenon is because larger ships are more efficient, and ocean shipping is a super competitive, low-margin business (during normal times) like the airline industry, so in order to eek out a tiny profit, ocean lines consolidate and build bigger and bigger ships, which further drops prices. These ships can only actually go to a handful of megaports around the world, though.

Another factor is the infrastructure that exists at the ports - you need to do something with the cargo once it gets on shore. LA/Long Beach has invested in big, efficient terminals for trucks and trains to get loaded quickly and move cargo out of the port in big volumes.

Source: I used to work at Flexport on ocean shipping, so I have a general understanding of the industry

[dmckeon]

Oakland is improving recently, to some extent: https://www.portofoakland.com/press-releases/biggest-contain...

The really interesting changes will be in the ports on the US Eastern seaboard which planned to take advantage of the super-panamax cargo ships dimensioned for the new channel at Panama.

[CameronNemo]

Why can't larger ships be unloaded onto smaller ships at sea? Then those smaller ships would have access to a wider net of ports. Like a river flooding out across a delta before it reaches the ocean, but in reverse.

[walrus01]

only the very tiniest of container ships have their own cranes onboard, anything above the tiniest size is entirely dependent on shore handling cranes.

also moving cargo between two ships floating around at sea is dangerous and difficult, giant ships are not meant to hold position parallel to each other in the open ocean (or indeed closely parallel to anything) without the assist of many tugs.

a "geared" (with crane) container ship looks like this, and even so it would be a very risky move to use the crane to do anything other than load a container to/from a wharf while the ship was firmly moored to it.

https://www.google.com/search?q=geared+container+ship&client...

[a3n]

Transferring items between ships at sea is not done while "stationary," it's done by both ships underway in parallel.

It's relatively dangerous, both ships have to be designed for it, and both crews have to be trained for it.

I participated in many such refueling and replenishing operations while I was in the US Navy.

https://www.google.com/search?tbm=isch&q=resupply%20at%20sea...

https://en.m.wikipedia.org/wiki/Underway_replenishment

[Ichthypresbyter]

The closest thing to this which has been tried was the LASH (Lighter Aboard Ship) system, where cargo was loaded onto unpowered barges that were in turn loaded on board a specially designed ocean-going ship. The barges could be unloaded more quickly than break-bulk cargo, and could be towed on inland waterways.

This proved not to be able to compete with container ships when they were introduced. The last LASH ships in regular commercial service AFAIK were the Baco-Liners, which served small ports in West Africa and were scrapped in the early 2010s.

[_-___________-_]

They actually still do this in Hong Kong, but not much, and it's unheard-of elsewhere due to the size of the cranes needed, most ships not having their own cranes, and safety concerns.

[janstice]

There was a similar system, which got more or less replaced by standardised containers - the LASH carrier fleet took freight in standardised barges called “lighters” which could be floated out at ports, but couldn’t really compete with the multi-modal train-to-ship-to-truck container platform.

[BurningFrog]

The gigantic cranes needed to load/unload a ship only exist on land, for several good reasons.

[zaroth]

That would require building the infrastructure in the form similar to a oil rig out there to facilitate the transfer.

This infrastructure would only be valuable or even necessary for perhaps 2-3 months every 5 years.

Who would ever finance that?