Maybe a little late, but it's my two cents contribution.
Rules first, as usual!
It is a requirement of Classification Societies ( ABS, Lloyd's Register of shipping, R.I.Na. and so on...), that an " OIL MIST DETECTOR" device shall be installed on every marine engine, used for propulsion purposes, whose power is superior to a certain value.
While this practice may save the engine from " crankcase mist explosions" due to dangerous situations arising in slow spees ( < 150 RPM) Two stroke engines, this practice has been demonstrated very little useful on medium speed engines ( RPM > 400 ).
As far as I am aware of technology latest development, the device is an opacity meter, with pneumatic drive suction from each cranckcase section. It is able to detect and alert in case a sudden elevation of opacity is revealed in the "oil fog" present in every engine section.
This practice is safe enough on slow speed engines ( the sudden increase on "foggyness" inside the cranckcase is.,timewise, comparable with RPM of engine. The reaction time of such a device is too long for four strokes medium speed engines. Simply put, when the alarm sound the engine is already falling apart.
This is not only theory, but indeed "direct burning experience" in marine propulsion plants.
Best regards everybody.
Sierra701