The Yanmar 1GM10 is the simplest of diesel engines, and mostly it just works. Its natural reliability can lead one down the path of negligence, however, and so it has been for me with regard to the zinc that is embedded in the cooling channels of the engine block.
The engine block has a zinc anode because it is raw-sea-water cooled, and because this water is frequently salt water, the potential for electrolysis within the engine block is substantial. The problem is that this zinc is hard to get to, requiring moving the alternator out of the way so as to get a wrench or a socket near the bolts that hold the zinc-bearing plate in the block.
Having done so, the plate comes off easily enough, and I had the zinc and necessary gaskets on hand. My intentions were good, you see... I've had these parts for two years, knowing that it had almost certainly been too long since the zinc was last renewed.
Nothing left. Not the smallest remnant of zinc to be found. Cold comfort, having been right. Bad form, my procrastination, and that of others before me. Below is what the new zinc looks like, installed on the plate, which was then re-installed on the engine block:
The actual renewal of the zinc anode took just minutes. Getting to it took 2 hours, and putting it all back together took 40 minutes or an hour. I'm resigned to going through this once every other year or so. Maybe again at the end of the trip north, as that should be about 500 hours, the interval the manual recommends for zinc renewal.