Unlike the Blue Coins in Bianco Hills, which were all available in a single episode, some of the Blue Coins in Ricco Harbor will require you to be on a specific episode. So, start with those, which only total four, then head to Episode 8 for the rest.
Blue Coin #1
You will need to be on Episode 1 for this Blue Coin. When you begin, head into the caged area of the ship right in front of you and clear out some of the goop. Underneath that goop will be a “M” shaped piece of graffiti. Clean it to get the Blue Coin.
Blue Coin #2
You will need to be on Episode 1 for this Blue Coin. There is a bunch of goop in front of the tower, with the scaffolding around it, near the beginning of the stage. Clear the goop to find some graffiti on the ground, so clean it to get the coin.
Blue Coin #3
You will need to be on Episode 1 for this Blue Coin. At the beginning, jump on the ship in front of you, then use the platform carried by the crane to latch onto the yellow maze-like contraption. Make it to the other side and use the next crane to reach the platform with two Pianta on it. If you look in the air, you should see a fan. Spraying this fan will raise a yellow submarine. Raise the sub all the way to get the Blue Coin.
Blue Coin #4
You will need to be on Episode 2 for this Blue Coin. At the beginning of the level, turn around and go across the logs to find some Blooper Racers. Take one and follow the trail of coins on the water, which will lead you to the entrance for the timed race. However, on the way there, right before the entrance, you will see a Blue Coin in the air, so jump and grab it.
Blue Coin #5
At the beginning of the level, turn around to see a building. On the side of this building will be some graffiti, so clean it for the coin.
Blue Coin #6
In the same area as the previous coin, Side Somersault and Wall Jump to the top of the same building, where you will see some more graffiti on the wall. As always, clean it to get the Blue Coin.
Blue Coin #7
Get on the ship right in front of you at the beginning, then get on top of the caged area. Inside the caged area, there is a Klamber climbing around on the ceiling. While on the outside, perform a Ground Pound on it to defeat it, with it yielding a Blue Coin.
Blue Coin #8
While still inside the cage from the previous coin, you should see another Klamber on the outside portion of the cage. Cling to the side and switch to your spray nozzle, then spray and punch the stunned Klamber to get another Blue Coin.
Blue Coin #9
Head on over to the tower with the scaffolding, then look at the side of the ship to find another piece of graffiti. Clean it to get the Blue Coin.
Blue Coin #10
There is a crate in the one corner, by the water, of the tower with the scaffolding. Break it open to reveal the Blue Coin.
Blue Coin #11 and #12
On the tower with the scaffolding, there will be a green X mark. This is one of those two-way pieces of graffiti, meaning the Blue Coin will spawn in another place of the level. The second X mark is located in the upper area, with all of the buildings, right past the fruit dispensers. To get the coin from the tower X-mark, you can Side Somersault-Wall Jump-Hover to the upper area, then jump, spray water and dive in the same motion. If done right, you will slide as if you’re on water.
The coin that spawns from the upper area X-mark is on a pretty short timer and it’s pretty much required to have the Turbo Nozzle. You can find a box on top of one of the houses in the upper area, so it’s not too bad getting back to the upper area from there. As soon as you spawn the Blue Coin back at the tower, switch to the Turbo Nozzle and blast down the path, jumping over the little wall and hopefully going straight to the Blue Coin.
Blue Coin #13
You will need a Rocket Nozzle for this coin and the next one, with a box found on top of the buildings in the upper area. Once you have it, return to the tower with the scaffolding and you will find a Blue Coin on a piece of scaffolding.
Blue Coin #14
While still at the tower, with the Rocket Nozzle, make your way to the top of it. You should see some coins in the air there, but there’s another Blue Coin at the top of that coin trail. In order to get it, you will have to rocket into the air at the apex of your normal jump.
Blue Coin #15
To the right of the ship at the beginning of the level, there is a crane that’s moving. You will need to get on top of the crane, where you will find the Blue Coin amongst some normal coins.