"I've owned three inboards and none have ever put out any steam."
Every boat I have ever owned, outboard, I/O or inboard would create steam out the exhaust. Water is being mixed with super hot exhaust, it's going to make steam!
When it is hot and dry out the steam may just disappear before you notice it. On a cold morning, however, you can create a fog around the back of the boat!
If it is noticable when you step on it then I doubt that it is steam. Watch you oil consumption carefully, it sounds to me like it might be burning a lot of oil. It is not unusual for an engine that sits for months at at time to become an oil burner at relatively low number of hours. Sitting all winter allows the upper cylinder walls to rust, which then makes the walls a bit rough, which wears out the rings when you start the engine in the spring.