It's been a (long) time since I logged in to this site, and things look kinda dead, but I'll give it a shot since there used to be lots of knowledgeable folks here:
I have a 1991 22' Dana day cruiser that I've owned since new. Bought a bare hull with the fuel tanks and an American Turbine 9.25" pump installed, and then rigged it myself over the course of a year. I ran an aluminum impeller until I switched out the pump with another 9.25" American Turbine pump that I bought as a "spare" a couple of years ago. I installed a new stainless 9.25" impeller in the spare pump, along with new bearings and seals. The idea was that this would be the last pump build that I'd ever have to do...
After the change-over, I had a lot of noise in the pump/driveline/hull. I then switched back to the old pump to verify it was something to do with the "new" pump, and the "new" noise went away. The stainless impeller is considerably heavier than the aluminum impeller, so I thought it might need to be balanced. So I sent the shaft and impeller off to ARS Marine and had them balance it. After it came back, I put everything back together and clearanced the assembly per standard procedure. The balanced impeller is better, but still noisier than the aluminum impellers that I've run in the past.
I also rebuilt the driveline, but the old u-joint bearings were still okay (no slop). The engine is mounted solid to the stringers (no rubber). I took great care to try and get the pump shaft parallel to the engine centerline, and the offset angle in each u-joint is about 3/4 degree to encourage lubrication of the joints.
This is a closed-bow boat, with the bow open to the cockpit. We store skis and stuff under the bow for easy access, so I don't really want to close it off. I have a feeling that the semi-enclosed area in the bow is acting like a horn and amplifying the vibrations being transmitted into the hull from the pump. But I'm at a loss as to how to reduce the pump vibrations without going back to an aluminum impeller (which I'm ready to do...). I've bought some sound mat that I plan to install on the underside of the bow deck this fall.
Has anyone experienced something similar when changing from and aluminum impeller to stainless?
Thanks in advance for your input!
Matt
