Time for the spring diesel maintenance. I made my list of all things to do and could not find the recommended change interval for the raw water impeller. How often do the masses change theirs?
"When cracks appear at the base of the blades indicating that it's about to disintegrate"
--- or something to that effect.
That's got my vote.
(You need to inspect the impeller every few hundred hours or as often as you feel the need to do so. There was a time when my RW pump was damaging impellers in 50 hours or less. I checked them more frequently then. The impeller I have in now has several hundred hours on it with no visible sign of wear. Go figure.)
PS -- I remove the impeller during the winterization process and re-install it in the spring. That way I check it at least twice each season.
It has always been a part of my annual spring haul-out routine; do bottom, change zincs, change impeller, change oil, change filters, etc. I'm cheap; routine maintenance is cheap, repair is not. Besides, the removed impeller can usually serve as an additional spare.
On the Morning Star, I pull the impeller when on the hard, and reinstall it when I put 'er back in. Usually Dec. to Jan. in La Paz, Baja. I'm with Main Sail, the $18 is nothing compared to burning up a motor.
"If you can't fix it with a hammer, you have an electrical problem"
I inspect mine in the fall as part of my winterization process. This past winter I saw cracks in the rubber at the base of the vanes so i replaced it. Since I motor about 50 hours a year, I figure I can easily get 4 -5 years from an impeller.
The impeller for my oberdorfer pump is about $50 by the time you add shipping and tax, so I feel that it would be needlessly expensive to change it every year.
I do carry spares with me, so I can change it if required.