By March 2024, Ukraine’s Navy spokesman Dmytro Pletenchuk said they had disabled or destroyed one third of the Russian Black Sea fleet.[7]
That being said, keep in mind that some of those ships are specialized and interdependent. Like, a seagoing fleet tug doesn’t do you nearly as much good without an aircraft carrier to tow and vice versa. So even aside from Ukraine focusing on more-valuable ships, I expect that even a random one-third of ships being lost would probably cause a greater degradation of capability than one-third.
https://en.wikipedia.org/wiki/Black_Sea_Fleet
That being said, keep in mind that some of those ships are specialized and interdependent. Like, a seagoing fleet tug doesn’t do you nearly as much good without an aircraft carrier to tow and vice versa. So even aside from Ukraine focusing on more-valuable ships, I expect that even a random one-third of ships being lost would probably cause a greater degradation of capability than one-third.