I/O, inboard, O/B? What type of exhaust setup? In almost all cases water is run through the exhaust to reduce the risk of fire and to cool components in a marine application. Water mixed with hot stuff = steam . . .
What your seeing could still be smoke, but that would take a visual. If it dissipates like steam, then it probably is.
Well if it lingers, and you can still see it after 10 seconds or so, I would agree with wvit1001 and it sounds like you are burning some oil . . . Does it use any oil?
I've got a '95 Stingray with a 350. It blows just a very little white smoke when it's first started but after it warms up and the motor tightens up that goes away.
