Installing a new impeller in a water pump can be a bit of a struggle, especially if you’re working under the engine by braille. That’s the position I found myself in with the Yanmar 3GM30F aboard my 1978 C&C 29, Elusive. Then I discovered a hack that makes this job much easier.
My struggle had to do with trying (unsuccessfully) to align the impeller vanes while twisting the impeller into the pump housing. My salvation came in the form of wire ties (they have so many uses aboard!) and Vaseline.
It helps to know the rotation of your water pump (I marked mine with an arrow, using a Sharpie). It also helps to grease the impeller and the inside of the pump housing with whatever lubricant is handy, but one that won’t harm the rubber vanes. Then, zip a wire tie around the mid-section of the impeller, just snug enough to hold the vanes in position and oriented the correct direction, then slip the impeller partly onto the shaft and partly into the housing, and slide the wire tie off the lubricated vanes before twisting it home. Voila!