Questions on ships

[Tiberius Clodius Corvinus]

I'm not sure it was so widespread (few resources?)... I always thought it was then and later usual only with warships and applied as a protection against woodworms and others, so it was up to the waterline ... there are drawings in Connollys "Roman Army", that show one of the ships from lake Nemi and its lead covering is surely at least a foot higher than the waterline
the appearance of the lead should be the way you describe it: grey ... lead oxidizes within minutes to that colour