For this we need to record how often the route is traveled. The more a route is traveled the stronger its connection, allowing for an easier, more efficient journey. However a stronger route will also expect a larger cargo or resources to be delivered. This would hopefully prevent islands in close proximity becoming locked together, as well as allowing a growth/development between them.
Rule 11: An island can create a boat and send it to any other island.
Rule 12: The greater the distance between islands the more resources needed to send a boat.
Rule 13: The more journeys made between an island the stronger the connection becomes.
Rule 14: The stronger the connection the less "resources" need to travel.
Rule 15: The stronger the connection the more "resources" needed as cargo.