White exhaust smoke

I'm not the expert....one will be along soon!
White smoke is often associated with water. It could be a bit in the exhaust system which just gets vaporised after start up but this should only last until the system is hot.
Water entering the engine can be more serious and the experts will fill you in there.
Generally any increasing amount of white or black smoke is an indication that something is going wrong and you should be 'concerned to find the cause'
 
Steam will disappear as it evaporates, smoke will fade as it disperses, but hangs around longer. A sudden increase in either should be investigated.

Causes of steam could range from barnacles in the colling water through-hull to a blown head gasket. White smoke could be anything from a tired injector to a cracked piston and broken rings, though I wouldn't lose any sleep if it only happens on start-up.
 
My VP2003 has always emitted white 'smoke' (although I think it's steam). I've had the boat 9 years and have given up worrying about it.
When I needed a new heat exchanger I thought it might change but it made absolutely no difference to the emission.
 
Pedant mode Mk2: steam can't evaporate. As Jumping Jack said, It's a gas. ;)
Pedant mode Mk3. ... Except you can't see Steam in gas form. What you see as steam is water droplets formed by condensed Steam - hence it actually can evaporate ...
 
Pedant mode Mk3. ... Except you can't see Steam in gas form. What you see as steam is water droplets formed by condensed Steam - hence it actually can evaporate ...

Another thing that's evidently unseeable is this from post #4: "steam, or water vapour, come to that, is invisible".
If you "can't see steam in gas form", then you can't see steam at all, because it only exists in the gas phase. Granted, in common parlance, what we call "steam" is actually something else (your water droplets).
 
The only time that I remember seeing copious quantities of exhaust steam it turned out that the cooling water inlet was almost completely blocked with bladderwrack.
 
The water emitting from the exhaust isn’t hot (bath warm) and there is no significant smell to it.
The oil is clean (no sludge on the inside of the filler cap).
I thought maybe a congested air filter but I can’t get the bloody thing off to check.
It started end of last year. The engine was smoky and sluggish. I checked the water filter as there seemed insufficient water coming out of the exhaust and it was full of hard mud. The resulting clean out seemed to have cured it but the white smoke/steam is back.
I’ve had three days of headwinds and the engine must be thinking what it has done so wrong to be worked so hard but apart from the white stuff has performed admirably.
 
The water emitting from the exhaust isn’t hot (bath warm) and there is no significant smell to it.
The oil is clean (no sludge on the inside of the filler cap).
I thought maybe a congested air filter but I can’t get the bloody thing off to check.
It started end of last year. The engine was smoky and sluggish. I checked the water filter as there seemed insufficient water coming out of the exhaust and it was full of hard mud. The resulting clean out seemed to have cured it but the white smoke/steam is back.
I’ve had three days of headwinds and the engine must be thinking what it has done so wrong to be worked so hard but apart from the white stuff has performed admirably.

Start of the season I had this - thought it was oil burning since it looked bluer to me than white. When engine revs increased exhaust was a bit like a steam train.

It turned out that the impeller had lost a blade and this had gone into the heat exchanger and was cutting down flow. Take a look at your impeller.
 
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