Further to Ant’s reply above, you can also get mussels and their shells blocking the waterway within the saildrive leg, so it’s a good idea during your lay up ashore period to fill the saildrive waterway with vinegar and leave it in there for a couple of days. This will soften and help to dissolve the barnacle shells and kill off any squatters that have taken up residence, but you will need to block up the waterway inlets in the saildrive or the vinegar will just run straight out of the bottom. See the photos below for the kit I used to block the saildrive waterways. The wood pads had some closed cell foam rubber stuck to them to make a seal, while the small bolt had a rubber grommet around it to form a seal which could be adjusted for a watertight fit.
Also, on my older Bavaria, a 36 from 2002, the sea water filter was, and still is, of a pretty poor design which allowed mussel shells to get past and through the cooling water pump to the entrance to the heat exhanger where they stopped and began to block the heat exchanger tubes. On top of that, the previous owner had not attempted to find the odd pieces of impeller blades that were occasionally lost, and these too were lodged at the entrance to the heat exchanger. I reckoned at the time that some 70 to 80% or more of the heat exchanger tubes were blocked by barnacle shells and pieces of the rubber impeller blades that had been lost during the time prior to me buying the boat. In consequence, and with insufficient cooling water actually going through the heat exchanger, I too had noticed steam in the exhaust outflow, but wasn’t sure if it was steam or white smoke until one day when the engine temperature alarm began to make a noise. Since then, and after removing all of the shell and rubber from the entrance to the heat exchanger, I have fitted an engine exhaust temperature alarm with display at the binnacle where I can watch the temperature.
