First...loss of oil is an issue. If you are not seeing a lot of black smoke AND ont seeing it in your bilge, then it is being pumped out in liquid form through your exhaust hose. Logical suspect would be the oil cooler or transmission cooler with a small leak.
Second...white smoke = vapor as CP says and it happens when you are under way rather than at the dock so I would check for restrictions in your water intake line, blockage in your exhaust elbow or heat exchanger.
What is your temperature gauge reading when you start to see the smoke? Is thermostat working?