Personally I don't own a boat to me they are nothing more than a temporary hole in the water that you pour money into.
Yes some perhaps many salvaging operations can be as simple as pulling a boat to the surface by allowing it to create its own lift due to hull design and forward movement,
The making of the ping pong balls just reminded me of the show I once saw where they tried several times to raise a sunken boat before they were successful.
Not all boats can be raised by the cable and tow method small pleasure craft or bass boats and jon boats sure but a cabin cruiser or just about any sail boat and all larger craft would require a tremendously powerful tug capable of attaining a good amount of headway. Even on small craft the sea cocks would have to be open and the boat would have to be towed sufficiently long enough for enough water to be evacuated before it could gain sufficient buoyancy to remain afloat long enough to be boarded and have the hull sealed. Temporary patches to a damaged hull if this was the reason for it sinking might be possible to install while the boat were on the bottom. If it were swamped due to a storm then it could be resting upright on its side or completely turreted. Or if it were resting near a drop off shelf or in a boulder strewn bottom there may not be enough area to pull it far enough for it to begin planing, that is why far more require the brute force of a barge crane or buoyancy bags even those fail sometimes if water cannot be displaced from within the cavities of the boat.
Maybe one might want to pump beach balls or inflate huge balloon type bags into the cavities then finish off with ever smaller balls until finally using ping pong balls to achieve at least neutral buoyancy.