With all due respect, as a hobby Junior and i have rescued a few old clunkers - sail and power -from hibernation and brought back to life. Some of them have been smokers in different ways so we have had to do a little research on the nature of the smoke. So i freely share my limited knowledge, which is worth every penny...
Blue smoke - can be bad, typically oil getting by piston rings, often associated with bad compression and worn out innards. Often leaves a sheen on water surface.
Black smoke - represents unburned fuel. Can be from a dirty bottom so motors overloaded, improper prop size or pitch, bad timing, bad injectors, dirty filter or coolers, or bad turbos or who knows what else.
White smoke - usually from water vapor which can be from water collecting somehow when she sits and you see it particularly at start up, from leaking head gasket (bad if you smell antifreeze in exhaust or water in the oil), from overheating during operation (where barnacle buster helps).
Technically i still have an old classic 32 foot Forest Johnson Prowler (long story but supposed to go to a guy in exchange for house remodeling work, which is incomplete). It has twin 200 HP Volvo turbo diesels which are the poster child for all symptoms. A little blue sheen and slow to start on one engine so some day may need a little piston work. Lots of embarrassing white smoke that goes away when she starts up. But none of those compare to the black smoke coming out the stern as she gets up to speed. Was not worried about the bit of blue nor the white, and the culprit for the black is two fold, needs timing/injector work, and has very dirty aftercoolers that need to be cleaned. If the guy finishes his work those will be his problem, fully disclosed.
So in your boat it sounds like maybe water vapor at start up. I would keep an eye on antifreeze level and look for water in the oil. If not issues probably not a problem. A barnacle buster bath is always a good thing.
That's my 0 cents worth!
