I reckon that their interface is not intuitive at all. So to send a boat to another port, follow these steps:
- Select your departure port
- Select the boat you want to send
- Select the sail icon on the bottom of the side bar
- Select your destination port
The UI is pretty inintuitive for different reason. Firstly the selection effect on the items of the side bar is quite light (a light blue circle on a blue background) and you really have to pay attention to see it. Secondly, it takes time to realise that the 3 buttons on at the bottom are actually contextual to the selected boat. And it gets even more confusing when you realise that some actions in the trading menu are not all contextual to the boat, but also to the port. For example buying a boat is contextual to the port but is activated throught the trading button contextual to the boat...