Salt Water Foot Pump = Broken/Spun Impellers

Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
This was an interesting phenomenon. In the last year and a half, I've been in the middle of a weekend trip and while sitting on a mooring somehow had failed impellers twice. At first, I chalked it up to inferior impellors, and was just happy I kept old spares. But then I realized something this last time and it dawned on my why they were failing. Here's the story:
It was after sunset and we were two days in having run the stereo a lot and some lights and things and I thought it would be smart to let the engine recharge for a while. Someone else was doing the dishes, and as instructed by me, they were using the foot-pump salt-water source for pre-washing and then rinsing with fresh water.
I start the engine and notice no water coming out. Remembering the last time this happened at the island, I go down and open the front engine hatch cover, first close the raw water intake and start removing the impeller cover. The person doing dishes exclaims that the foot pump stopped working, I say "oh yah, I just closed it's source of water, it'll be back soon, use fresh water for everything for the moment". Then, with the impellor cover off, I re-open the raw water valve and plenty of water gushes out of the pump housing, so next I have someone crank the engine for a moment and I can clearly see that the impeller is not turning but the shaft is. OKAY--- I know what the problem is and I have a spare, so I pop an old one in, close it all up and start the engine -voila! Everything back to normal.
Then, I started wondering how it could have happened? And I then started to think about the sink water/foot pump and how much suction that thing really has on it. And then, I figured it out. There was probably not only all the water from that through hull being sucked into the sink, but probably a whole bunch of negative pressure on that water pump too. Since we all know how delicate those things are, that must be the reason it failed.

Now, I do love the salt water foot pump. I have honestly never read any specific instructions for it, I just sort of figure it out on my own. There is no other raw-water intake other then the sink drain and the engine raw water intake that it could possible get salt water from under the galley, so this must be how it is intended to be setup, but now I'm going to have to make a rule that it is NEVER used while the engine is running.

Has anybody else run into this? Is this something that I was supposed to be aware of and just missed the instructions?
Is anybody else setup differently who also has this optional setup?
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
I'm going to have to make a rule that it is NEVER used while the engine is running.
Or.... you install a thru hull valve and hose for the foot-pump. Everyone is happy. Dishes are washed without regard to the engine running.
 
  • Like
Likes: LloydB
Feb 20, 2011
7,990
Island Packet 35 Tucson, AZ/San Carlos, MX
Since we all know how delicate those things are, that must be the reason it failed.
You never stated what exactly it was that failed. Is there a spline on the hub that dissolved? Got sucked out?

Hard (for me) to imagine your foot pump overcoming the raw water pump.
 
Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
You never stated what exactly it was that failed. Is there a spline on the hub that dissolved? Got sucked out?

Hard (for me) to imagine your foot pump overcoming the raw water pump.
It was "spun" as stated in the title. That's when the center shaft spins but the rubber part around does not.
No water in the pump will destroy the impeller quickly. So, having all the water sucked out and negative pressure on it I'm sure will destroy it. It's happened to me twice now, and that's the only thing that explains it.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
I have heard of that happening to impellers from discount sellers.
It could be a manufacturing issue and or coupled with the possible over heating of the pump (pump running dry).
 
Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
I have heard of that happening to impellers from discount sellers.
It could be a manufacturing issue and or coupled with the possible over heating of the pump (pump running dry).
I have only purchased one on the internet before, and I keep getting them from my local marine hardware supplier. I'm now confident the failure was caused by the raw water foot pump suction. Whether or not quality isn't as good from one to the other, the foot pump issue is a concern for me.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
I can understand the concern. It appears to be reasonable to me. Connecting the pump to it's own thru hull would resolve the issue. I have one as such, It is a 1/2inch thru hull. It is on more thing I have to monitor. I am thinking about attaching a wash down pump to the same thru hull.
 
Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
My anchor locker washdown pump is connected to the head drain/intake through hull.
 
Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
I reported the incident to Oberdorfer, and they actually called me. The tech that I talked to agreed that only during the initial startup, the foot-pump could possibly prevent water going to the engine and damage the impeller. It doesn't take much, he says. If it's dry at all, it will very quickly heat up and spin out like that. But he thinks that once the engine is running that it is unlikely that same foot-pump could prevent water going into the impeller.