Super Mario Sunshine/Corona Mountain blue coins

After the 1-Up
After the 1-Up mushroom placed on the broken sidewalk, there should be another broken sidewalk with the blue coin in plain sight.

After Using The Boat
Before getting off the boat, there are 9 blue coins placed around the sidewalk with the Rocket Nozzle box on it. You can use your boat to get all of these, however, it is fairly hard, and will probably not take you one try. Another method to getting these coins is using the Hover Nozzle to get to the desired blue coin, die, and repeat the process. To do this method, make sure you always grab the 1-Up placed on the broken sidewalk.