OK, so I was sent to the Marshall islands to patrol and sink merchants. I get there with 80% fuel to spare, and it's quiet, so I head off towards Saipan. There were some task forces around but I didn't see them, so I decided to avoid the airbase and went into Guam instead to blow some stuff up.
I tear a small merchant in half with two hits, then I concentrate on a big juicy tanker. Fire tubes three and four, good hits low on the hull. Target buring, alls good... Fire tube 5. hit about one foot above the keel. Fire tube 6, perfect keelshot. I turn to something else and blow up a large modern cargo ship with 3 shots from the stern tubes... but the tanker hasnt sunk! I fire tube 10 at it, again hit just above the keel.
I turn around, engines stop, and wait two hours. Fire tubes one, two and three at it, all hit, at least one keelshot... nothing. not even any list. I made my quota by gunning somethingelse and went home!!
8 hits, at least 2 keelshots, and the tanker was still there, alive and well!!! WHAT THE ****!!!!
There are a couple things. One, being docked MIGHT alter the way things sink (not sure). Two, shallow water can certainly present a problem. If the ships doesn't reach a certain depth, it will never count for sinking. If the water is too shallow, it will never get to that depth.
It's not far fetched, really, look at Pearl Harbor, all but 2 of the "sunk" BBs were refloated and fought the japanese later.
Port attacks are very weak in SH4, it's pretty much a joke, the only difficulty is that things don't always sink. Not bad compared to RL
Tankers are pretty tough customers thanks to their extensive subdivision, and can survive several torpedo hits (especially in ballast) as long as they don't blow up- the "Ohio" being a prime example. The point about sinking in shallow water is also valid, but not only for tankers- there are numerous examples of the Japanese salvaging ships sunk in shallow water and restoring them to service.
From my experience it was most likely due to shallow water. I've been out in the open ocean and have "sunk" ships in areas where the map showed white. Although I got those satisfying secondary explosions, I would not get credit for a kill if any part of the superstructure was still above the waterline when the keel was on the bottom. If you are attacking a harbor it's even more likely to happen. My guess is the coding for the game requires the sinking vessel to pass some depth before you get credit.
point taken but I got a kill for a heavy transport ship when half the bow was out of the water at 45 degrees and the stern was in the mud. The tanker wasn't listing or anything, and it was clear of the rocks by a long way (i accidentally sailed my sub under it while trying to turn around).
I got Trigger Maru 1.6.2 in the meantime, ill have fun with that
I went through the same problem until I solved it. You need to make it explode and it will count for a sunk ship. All you need to do is to fire three torpedoes (especially at a tanker, explosion is often one of it's virtue) on the same spot (more or less 8 feet around the first hole). That hole ought to be started, however, (if you divide the ship in three parts -Bow div., middle div, Stern div.) in the forelest part of the Bow division. Be aware that sometimes keel shots are not working on docked ships for their draft is different than when at sea. So if you fire a torpedo try a lower depth than you thought first but about 5~10 feet lower than the waterline (unless of course it is lower than the keel).
It rarely go to a fourth torp before you hear/see a huge explosion.
krazy is right...dunno why but the ships that seem unsinkable in harbor need to have a secondary explosion induced either with a torp shot to the right spot or deck gun. Once that happens they go on your log.