I am the previous owner of a C&C 30 with a 2GM20 Yanmar engine. I actually does matter; some transmissions are not meant to free wheel. This was the case with my Yanmar. Actually, I believe that they suggested that you put the engine in reverse to lock the shaft. If you don''t have you manual, call a Yanmar dealer. A locked shaft is good both for your engine and for your performance under sail.