The Piranha comes weighted and balanced from the factory for neutral buoyancy in fresh water. For saltwater use, install the provided weight plates. The weight plates come weighted for the brackish water of the Pacific Northwest region. For use in saltier water, such as the Red Sea or Mediterranean, add the black weight tabs supplied in your spares kit to ensure proper buoyancy.

For a P1, there are 3 saltwater plates:
- The nose plate, located under the nose
- The battery plate, located under the battery
- The tail plate, located on the battery with the battery plate
For a P2, there are 4 saltwater plates:
- The nose plate, located under the nose
- Battery 1 plate, located under the battery
- Battery 2 plate, located under the battery
- The tail plate, located on the battery closest to the tail with the battery plate
For a P3, there are 5 saltwater plates:
- The nose plate, located under the nose
- Battery 1 plate, located under the battery
- Battery 2 plate, located under the battery
- Battery 3 plate, located under the battery
- The tail plate, located on the battery closest to the tail with the battery plate