"White smoke" normally indicates "water" (as opposed to "black smoke" which normally indicates "unburned fuel").
Cause of "white smoke" can be:
A - In a "dry exhaust" - cold engine (i.e. engine not warm enough to discharge water in exhaust [products of combustion] as steam - which is a colourless gas). Normal during first 10-15 minutes but can also be caused by thermostat valve opening before engine reaches correct running temperature. Usually observed on cold mornings (in other words every day this year!!).
B - In a "dry exhaust" system water leaking into exhaust or into cylinder (via cracked head gasket or cracked head) will condense when meeting air and cause "white smoke".
C - In a "wet exhaust" system - insufficient water flow (i.e. water turns to steam in exhaust pipe and then condenses into water vapour when reaching air).
D - Engine has just announced failure to decide on a new Pope. (Or is it - just elected new pope? I can never remember.)
Pretty sure that the white smoke appears when they *have* decided new pope. Otherwise they'd have smoke all the time and a bit of a coughing splutter for everyone in Vatican.
Boatwise, I wd check the inlet primary filters. Then um the secondary water levels, and then mebbe headbolt tightness with torque wrench. If it goes away when warmed up, then wd forget about it (although that's just my forgetfulness, not that it doesn't mean it isn't serious)
The only time we had a serious amount of white smoke was after cleaning out the primary fuel filter and not quite getting the gasket back right.
Engine ran quite well, but was actually being starved of fuel, in other words air getting into the main feed line, before the lift pump. It is quite easy to get an air leak, which doesn’t correspondingly allow fuel out at rest; hence it may not be at all obvious.
Suggest checking all the fuel lines and joints from tank to pump.
Almost every Bukh 20 engine emits steam. It seems to be a function of the relatively low water flow, the bypass system and the location of the water injection to the exhaust. Nothing to worry about. Don't know about other engine sizes.
John, If it is any consolation to you, I own a Westerly Fulmar,Bukh 24 engine, with the same "problem". I raised a similar query to your own on the old Forum. The most interesting reply I got was from the Westerly Owners Club in the Netherlands who had raised the issue with Bukh who told them not to worry as this was common to most Bukhs and not a matter for concern. Hope this is helpful.