I apologize for no audio, as i'm feeling super under the weather. Here's the first 6 locations you can get this at. You get two to progress, and the other four are attached to buoys on a chain. Just grab them with the crane on the back of the ship, lift them up into the boat, and take the fuel.
1. When you attach the new hull, you are forced to get one here.
2. After leaving the new hull area, there's a buoy where you can get one.
3. When you first get the submarine ability and go underwater, you have to get one here at the underwater door.
3. After this underwater submarine area when you resurface is a buoy.
4. After the long stormy area before the crane, there's a buoy here.
5. After launching the boat from the floating city, there's a buoy right here.
There's at least one or two more, like after all the ice areas. It's right at the waterfall. I think there might be one after the waterfall too, but not 100% sure.