The Drive provides information showing the results of Ukrainian Unmanned Surface Vessel (USV) attacks on a small Russian tanker and a Russian Navy LST. Reportedly the USVs were equipped with 450 kg of explosives (about 1000 pounds). The explosions occurred essentially at the waterline. Had the explosions occurred well below the waterline, or particularly below the keel, the effect would have been greater. Even in the photo above, it appears the explosion cause more damage below the waterline than above. Had it been well above the waterline, the effect on the ship would probably have been less, but similar sized bomb or missile hits on the superstructure would likely have caused more personnel casualties.
Our First Look At Hole Blasted Into Russian Tanker By Ukrainian Drone Boat
Chuck Hill's CG Blog 
Information on the Sept. 13 attack on sub in Sevastopol shows she was hit twice. Once on the bow and once starboard side aft of the sail.
https://www.navyrecognition.com/index.php/naval-news/naval-news-archive/2023/september/13577-submarine-rostov-on-don-suffers-critical-damage-new-photos-reveal-extent-of-september-13-attack.html