Hydrocarbons v Ammonia for IC engines.

That's obvious...

It is and it was, but the world wasn't ready for them.

One of the problems apparent is getting approval from the various ports to allow them to dock - quite a number refuse to allow nuclear powered craft to dock at the moment.

There was also a suggestion that you could build floating ammonia generating/storage/transport ships. With a nuclear power plant they would have ample electrical generation capacity to split water and make hydrogen thence ammonia while floating, and offload ammonia to storage facilities at the ports for them to use to refuel other ships.

They were banned from entering most ports

NS Savannah did run for a while but was expensive to run due to high crew requirements and difficult loading

It's also worth mentioning that Russia uses a fleet of nuclear-powered icebreakers to keep their northern ports accessible during winter. Of course, in (AGW) theory, they should be redundant by now!

True, but my point was that technology for production and handling has been around forever (well almost). And presumably we are already producing it by the lowest cost route.

Capital cost. And Bunker Fuel is *cheap*.

i.e. by using fossil fuel ;-)

Where they make perfect sense. They can stay at sea more or less forever, and since they use conventional Rankine cycle steam turbines there is no shortage of low grade heat to keep the crew comfortable.