3 bearing engine - steel crankcase

[Lowespeed]

My Thetis marine engine had an aluminium crankcase, although the whole engine was covered with a red paint not unlike red oxide but thicker and tougher. I thought this may be some sort of protection from water damage.
As an aside, the late Arthur Davies had a cast iron crankcase which he painted with aluminium paint and stood on the end of his stalls. He always enjoyed customers picking it up to ask the price !