Recall that I have a 1977 42' Californian with the 185HP Perkins 6.354MGT engines. I'm burning what I think is decades old fuel, the engines start instantly, and have white smoke (but not steam) at the slip, which seemingly cleans up underway. Upon returning to the slip after a work-out, there is still some white smoke, but much diminished, all injectors show the same temperature from the outside with an IR thermometer, and the tachs seem to be reasonably consistent with a hand-held optical tach. I'm seeing 2050-2100 RPM WOT under load and 2800+ out of gear. The boat does move more than full-speed, 14+kn, WOT, but gets some grey in the smoke just as I get to WOT ROMs. (I know I shouldn't do that often. I just did it a bit to measure performance). The boat has 23x21x1-3/8" props, which according to the build sheet post here, is most likely how it was originally delivered.
My goal is to eliminate any graying of the smoke at WOT, get the boat to the spec'd RPMs, and hopefully let the white smoke clear up with eventual new fuel.
My mechanic told me that over-pitching props isn't uncommon because it lets them run at lower RPMs and therefore quieter. The prop shop said the same thing, except that some people do it to try to squeeze out a little better performance at higher speeds.
When I got the props hauled, they were too rotted to be worked, so they are being replaced with new ones. The yard advised against trying to find used ones and then tuning them.
Based upon what the prop shop tells me, I should go to 23x19x1-3/8" to get the spec'd RPMs into the correct range, which should improve fuel economy and engine life, and eliminate the grey smoke entirely. They said, if I'm unhappy with the new props and decide that I want to split the difference and go to 20" pitch, they'd discount repitching them to $150/prop.
I also need a strut replaced, so it'll be about 3-4 weeks before the part comes in and I have the boat back. I'll post an update then. But, in the meantime, did want to share what I learned, in case it is helpful to anyone.
Thanks again for all of your help!