Barge in tugboat

Similar to the ships, but moving cargo, liquids and raw material within the island
Since Bridges can’t do pipes and conveyor belts. You can combine the dredging machine someone mentioned with a barge. And the barge can dump to terraform maybe 2 to 3 dump truck loads in the barge

I like this. You'd want to add some basic docks that can serve as storages accessible by boats, trucks and transports. A dredging barge could be like the amphibious excavator but can dig deeper, down to minus 15 or 20, but only directly below itself, and can be served by barges or by amphib trucks for either fueling service or ore collection. I like the idea of maps where the rarest ores like titanium or uraninium are only on the seabed and deep mining tech is required to get at it, and it would also be useful for plopping asteroids in the drink and still getting at the goods.
There would need to be a fuel station for barges that is built on the shore, and tugs that are assigned to it become oilers. A boatyard that serves as the vehicle depot for boats would be needed as well. Also, if we're going to collect mixed ores in a boat we'll need a sorting plant that can be accessed by sea.