[Nocturnum]

Good work fred. I live in Japan and can tell you that all the passages between major islands are navigable by ship. Just note, in the area around Kobe/Osaka and anywhere near Tokyo bay/Yokohama you'd need to remove lots of man-made islands (for industrial or residential purposes)that were built in the 1970's and 80's. I happen to live on one of them by the way.