Submerged bodies do not experience hull speed.
Hull speed is a wave phenomenon. Simply stated, the waves generated by the hull moving through the water become longer as the speed increases. When the wave length equals the waterline length, the boat faces maximum bow and stern peaks of a single wave that require a large increase in power to overcome. This is hull speed.
Cavitation is a limit of underwater speed. Where a shape curves back toward the centerline underwater, low pressure is generated. Since water is not compressible (like air) this low pressure sucks water down the curve. At some speed, the pressure is so low that the water vaporizes, generating vapor bubbles with very low pressure inside. When these bubbles move to an area where pressure begins to rise, they implode forcefully, easily damaging the surface for the underwater body. This is cavitation, and it is loud, and can do serious damage (and, I suppose, pain in a living body, a tuna for instance). Cavitation does not slow an underwater body directly, but quickly creates enough damage to compromise performance at high speeds. Cavitation seriously pits high speed propellers. Submarine propellers are designed to postpone the onset of cavitation because of the easily detectable noise it makes.