I've passed plenty of these on the high seas enroute to Europe from China, and no, the booms are left as in the picture. I have also seen them with the booms raised as you see them in port when not working!
As most of these carriers are converted tankers/bulkers, I can only assume they are suitably ballasted for stability, and their transits are weather routed.
Its interesting to see a port with cranes coming over the horizon in the middle of nowhere, only to see later they are a ship in transit.
I would imagine that the cranes are brought down to nearer deck level when at sea,
or is it just a harbor vessel?Has it got a rolling deck for stability?
john