Charybdis was designed to be slightly positively buoyant in water. This ensures that the vehicle will float to the surface if there is a systems failure. A high riding moment is desired to control the pitch and roll of the vehicle. The central disk of the vehicle should remain flat and parallel to the surface plane. This keeps the sensors in their ideal configuration and allows the thrusters to operate properly. A high riding moment is created in the AUV by dropping the equipment with high density low into the vehicle, and adding flotation to the top of the vehicle. A 2lb weight rack system was installed beneath the battery tube in order to keep the center of mass close to the center of the vehicle. 8lb density foam was created from a 2 part mixture. The foam was molded to the top shell, and provides adequate flotation and balance for the AUV.