You had river gunboats as convoy escorts??? They might escort a small inter-island convoy, but shouldn't be on the open sea... Also, they are Type=0 and should have sound associated with them... Digging some more.
Now, what do you consider a "Patrol Boat"? To the IJN, they were the older second class DD (Minekaze, Momi & Wakatake)... either way though, unless they are a Type=104, you should hear them on sonar...
