I ought to thank people again for ther help in my questions about this. In the end, last week, I did a short but very pleasant trip that gave me at least a taster of the inland sea. I was staying, with my son, in Osaka, so we took the Shinkansen to Hisoshima and from there took the car ferry to Matsuyama via Kure and return. Time and logistics made anything else impractical. Very glad to have done it though.