Abd_von_Mumit... good point, well made.
Clyde00... yes, I've always been saving on the surface in calm waters, away from land. Perhaps it would be safer to choose my next savepoint at base, and then try saving again at sea?
Paajtor... that sounds very interesting, and it makes sense. The problem could well be with a corrupted .tmp file.
*Many* thanks Kaluens; really appreciate your support. I'll let you know what works and (hopefully) add to our SH3 general knowledge.
Tim, UK