I examined Wartime Shipbuilding History, Ichiro Onozuka, since was doubtful about that bilge keel might be omitted in the drawing, but could not find any explanation about it. Aside of it, related description to type 2A was, ‘bilge radius was took minimum to enable one-plate covering’.
Sorry, I don’t know the term Class NK. If it indicates pre-war group it might not be used domestically, like Class AM submarine (I-13 class). Please tell me the ship’s name.
At the same time you met Yamato survivor I had been practiced with an older coach in kendo club of school who was once aboard on HYUGA.
attached image, Hisakawa maru