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 Post subject: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ??
PostPosted: 12 Sep 2012 08:44 
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Midshipman

Joined: 05 Apr 2011 17:27
Posts: 66
I did a "search" on the forum but could not find anything on this topic. Both a 6-blade and 12-blade impeller are available for the sea water pump pn my W50. The diagram in my T37 parts manual shows a 6-blade impeller. I'm wondering if there are any thoughts on this. Logic tells me that the larger the blades (6-blade), the less likely it will be for a broken blade to escape the pump housing and pass into the heat exchanger. I've used both types and they both keep the temp at 180 degrees.

Any thoughts?

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Mark
Celtic Lady, Hull #315
Muskegon, MI


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 12 Sep 2012 10:20 
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Skipper

Joined: 27 Oct 2006 10:32
Posts: 827
I'm no hydraulic engineer, but I would venture that the 6 blade would deliver more water at a slower rate and the 12 blade would be less water at a faster rate but what difference.........??? Not quite sure.


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 13 Sep 2012 02:51 
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Skipper

Joined: 20 Oct 2006 16:10
Posts: 687
Location: Out of Waukegan, IL
I would go with the 12. Volume would be the same unless the body of the impeller has a different size. You would just have twice the space between vanes and the vanes would be pretty much the same size but squishing out twice the water. So losing one vane would be more of a loss on a 6.

But I'd check the parts breakdown on the manufacturer site of the pump. I can't see the same pump housing working with 6 and 12 vane. The cam size would need to change to get a 6 vane to bend enough to squeeze out all the water. Each vane would have to be long enough to reach the next vane when bent down by the cam making a smaller body and bigger cam. The W50 manual has many drawings that don't always apply. If you have a Sherwood, they have great docs on their site which I posted recently or you can just google.

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SMMO/First Mate aboard High Flight #299
1981 - Full Keel - Furling Main (A boat for the lazy crew...)


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 19 Mar 2013 10:17 
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Midshipman

Joined: 05 Apr 2011 17:27
Posts: 66
This is an old post which I initiated but can share a couple of things to address comments or questions that members have posted. According to Torresen's Marina, you can still get the 6-blade impeller but it is about 4 times the cost of the 12-blade replacement impeller. Both fit the pump which I believe (mine anyway) is a Shurwood (sp). When I bought the boat and changed out the impeller the first time, it was a 6-blade. Because the blades were bigger, I found all of the rubber pieces still inside the pump housing with one piece lodged in the port heading to the engine. Since Torresens did not stock the 6-blade, they looked thru their catalogues and sold me two 12-blades (one for a spare) saying that the 12-blade was the suggested replacement unit. The only problem I found this year is that when I went to change the impeller, I could not retrieve all of the rubber pieces as with the blades being smaller, I think they were lost through the port and into the heat exchanger. There were only a few small pieces missing so I'm not going to dismantle and clean my heat exchanger quite yet. But my concern is that with the 12-blade impeller, I'm always going to have this problem and will have to be more precautionary, changing out my impeller more often.

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Mark
Celtic Lady, Hull #315
Muskegon, MI


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 03 May 2013 17:47 
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Skipper

Joined: 20 Oct 2006 16:10
Posts: 687
Location: Out of Waukegan, IL
I posted a simple retrieval process for vanes that make it to the heat ex. But most likely you'll find them if you remove the pump. They're jammed in the outlet and you don't see it when changing the impeller in place. They get jammed in the elbow as they make for the exit.

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SMMO/First Mate aboard High Flight #299
1981 - Full Keel - Furling Main (A boat for the lazy crew...)


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 26 Jun 2013 05:03 
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Skipper

Joined: 09 Jul 2008 12:51
Posts: 251
Not sure this is a good idea but with all of the potential problems with broken impeller blades heading for the HX I wonder if a simple strainer addition just past the sea water pump would do the trick. Although the blades could get caught in the pump neck exit the strainer would catch anything else. It would make it a good visual check too. Good idea or bad ?


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 27 Jun 2013 06:26 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
In the standard W50 setup, you essentially have a very limited place to look for shed impeller blades. They will be found between the pump outflow and the cap on the heat exchanger. Not much to disassemble for inspection. Just be sure the cap is aligned properly on the end of the exchanger when you put it back together. I always found this a challenge.


 
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 Post subject: Re: 6-Blade or 12-Blade Impeller for Sea Water Pump on W50 ?
PostPosted: 05 Jul 2013 17:04 
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Skipper

Joined: 10 Dec 2006 15:14
Posts: 213
Location: London, Ontario
I recently to my HX out to remove a broken zinc. When I looked at the tubes inside it I found 4 pieces of old impeller blades so they can get through to the HX. Perhaps a strainer would be a good idea.


 
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