There are these things as well newatlas.com/environment/wings-cargo-ship-efficiency/ You'd think that Andrew Forrest would be keen on them, but maybe not since iron ore cargos spend a lot of their journeys in the doldrums
There is a pun in there about hoping this idea floats. Regardless, it would be fab if they get the economics, and logistics of variable delivery times, etc to all work effectively in the market.