Not quite what we see in practice, this is born out by research
and practical trials on commercial
Here is an intersting piece of research
which agress with our findings.
Firstly lets clarify that a water
lubricated bearing when running does not touch the shaft so the only opportunity from wear is at start up and run down. Solid hard bearings have solid lubricants and can support the shaft with low friction when dry or during this period.
Soft materials such as nitrile rubber will allow sand and grit particles to enter the water
film area which supports the shaft, if they find their way in from a water groove the gap gets smaller, at some point certain sizes of sand or grit will not be able to pass between shaft and bearing. With a soft material the particles can imbed in the bearing surface creating an abrasive surface.
Hard materials faced with teh same grit or sand particles will see the grit/sand in the water channel. as it tries to enter the boundary between shaft and bearing at the narrower areas if it won't fit it will bounce along the edge until ejected it can not force its way in without moving the shaft, the water pressure of the supporting film will not allow this.
If the sand/grit particles can enter the boundary area it will be small enough to pass through, it may at very wosrt tear a piece of the bearing material out whilst scoring the shaft slightly but it won't stay there to continue to wear the shaft.
Currently the best material for water lubricated shaft bearings is a phenolic composite with surface chemistry which resists marine
growth (another large factor in wear rates) advanced surface polymer that helps prevent marine
growth on the shaft and integral dry lubricants. Aquarius is the most advanced of these new materials but there are a wide variety to choose from. Many are made from different polymers and have widely differing characteristics here are some Orkot, Railko, Thordon. If you search for composite marine bearing you'll find most of them.