The Boathouse is a location in Super Mario Sunshine. It can be found on the west side of Delfino Plaza at the end of a short dock, and is run by two Raccoons. After Mario collects his third Shine Sprite, the shop will mysteriously vanish, and a Polluted Piranha will take its place. After Mario defeats the Polluted Piranha, the shop rises out of the Goop, at which point it becomes apparent that Shadow Mario has painted another rainbow "M" on the side of the shop, similar to the one he had previously painted on the base of the Grand Pianta Statue. This "M" will lead the player to Ricco Harbor when entered.
After the shop rises out of the Goop, it will not immediately be open for business. However, if the player collects a total of 10 Blue Coins at a later point in the game, they can return to the shop and exchange the collected Blue Coins for one Shine Sprite, which will immediately be collected by Mario. If the player has less than 10 Blue Coins when they visit this shop, the Raccoon father will exclaim that he cannot drop his prices that low, and insist that the player collect more Blue Coins before he can sell them a Shine Sprite.
The player can have more than just 10 Blue Coins when they come to this shop, but the Blue Coins can only be traded in increments of ten. As long as they have enough Blue Coins to pay the Raccoon father though, the player can acquire as many Shine Sprites as they want when visiting the shop, as there is no limit on how many Blue Coins they can spend at once.