Stuck ships?

I'm aware of the bug regarding trading slots and adding warships to them - this is not that.

First few turns in the GC playing as Britain, I send a small trade fleet of an Indiaman, a sixth-rate, and a couple brigs to the Ivory coast. It arrives and can't move. It's 'stuck' on top of a Spanish fleet, which also seem to can't move.

There's a little green radius around the fleet that suggests I can move at least out the Spanish ship's radius, but I can't actually click on it - I get 'ships sail on the water!' voices, etc.

Is there anything to be done other than scuttle my fleet?