From: San Diego
From Nelson to Vanguard, Warship design and development, 1923-1945, by D. K. Brown, Naval Institute Press, ISBN 1-59114-602-x, pg 159:
Of 134 ships hit by one torpedo, 99 sank, and of the 35 which reached port, 17 were not repaired (ie constructive total loss). The smaller ships, corvettes and frigates, had little chance of surviving, and, in fact, only 2 out of 34 got home. Destroyes did a little better with 11 out of 48 surviving, and if the smaller, older ships are omitted, these figures improve to 11 out of 39. However, of the 10 repaired, none rejoined in less than 8 months. Of 15 destroyers hit by two torpedoes, 2 survived, while, not surprisingly, both those hit by three torpedoes sank. The sloops and frigates did even better with nearly half surviving (22 out of 47), and three of those lost were scuttled for immediate tactical reasons. That 16 were not repaired was due to the ready availability of replacements.
He is speaking only of the RN warship experience, here, not merchant ships.
The author eventually explains why more sloops and frigates survived two torpedoes than destroyers. From page 163, "back breaking":
Not surprisingly, there is an indication that the more highly-stressed ships were more likely to break their back. The most vulnerable ships were destroyers, highly stressed, and with a break of forecastle amidships which would much increase the stress locally. They were also shallow, keel to deck, which meant that a hit would destroy a higher proportion of the hull girder than in a deeper ship. The converse of this is seen in the sloops with low stress and a deep hull. USN experience is somewhat similar, of 30 sunk by above water attack, 6 broke their back (37%), whilst of 27 sunk by underwater weapons, 19 (70%) broke their back.
I am a bit hazy, at the moment, on were to find the stats for the damages inflicted by the US Silent Service on the Japanese...