Confirmed:
The Medium Cooler (NL_B) is very similar to the Soyo Maru (NL_C) in appearance. The main difference of course, is the superstructure of the NL_B is aft-mounted (that doesn't sound right...) and the Soyo Maru is midship. They have the same hull. In my current install, it looks like the Soyo Maru does use the NL_B image. It looks like you are using the latest / greatest
Nippon Maru and
Nihon Kaigun versions, but be sure you are using the newest Combined Rosters file from the mods. We've put the bloodhound on the trail of this... For now, here is
JP_SoyoMaru_fix.7z
Put this on top of all that you have, and it will copy an NL_C sil file named "JP_SoyoMaru_sil.dds" into the SoyoMaru folder, and you should be golden...