To be honest, I did went through the forum about this, and here is the topic of one person asking for information about island breakers (
Island Breakers).
As you can see, not all the information was given there, and that also misled some of my guild mates, that were in the process of building the island breakers as well.
I'm not blaming you, just saying that the game should give clear information about things like this in the menus. I've also heard that, even if the island is big enough to be looted, it is not sure you will be able to grab anything, even in stock. Gambling like I did can be risky further in the game.
I also think that the rules that are set are a bit to high. I really wish the older formulas were set back, and the island tiles available in stock, should still be something to be looted.