It can be very difficult to tell if the smoke behind your boat is normal or signals the start of a problem .
On a humid day you might find that you are followed by a dense cloud. In most cases this is normal.
You should be concerned when you notice an increase in this cloud under other wise normal conditions.
If the cloud is steam or water vapor, it is white and will totally dissipate behind you. This could be the first sign of an overheat. If the cloud is sooty or has a blue cast to it, a serious problem is indicated as this is smoke from oil, unburned fuel or burning exhause hose!. Smoke will not totally disappear, and you will see a trail for miles.
In either case (excessive steam or smoke), you need to turn off the engine and determine the cause of the problem ASAP !