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Old 18-05-2012, 08:17   #1
Cap
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Fuel Polishing Questions

I moved this from the multihull section; maybe i'll get a response here.

I know there are many threads about fuel polishing systems, but I haven't run across answers to the following questions.

Considering I have a 1984 35ft. Witness cat, with a 17ft. beam and I'm putting the polishing system in the port rear berth:

1. Will I have issues with the starboard engine starving for fuel? The engines are 13hp Nannie diesels. Would a typical fuel pump be able to handle the extra distance, or would that be straining it?

2. Would I need check valves in the system?

3. Should I include an in-line fuel pump to ensure the starboard engine will get plenty of fuel, or would that cause problems?

The polishing system I built brings the two tanks together to go through the polishing filter and pump, but each tank can be isolated in order to polish the fuel and return it to its proper tank; or I can move fuel from one tank to the other, or bypass the polishing system all together.

My concern is the extra distance I'm creating for the starboard engine. I'm also moving all filters to the polishing panel to ease maintenance; except the filters on the engines, of course.

Would running the fuel through the polishing system while under way cause any issue? This would basically mix the fuel from both tanks, and then split it out to both engines, but the polishing pump would certainly alleviate any issues about the whether or not the starboard engine fuel pump could handle the increased distance...

I'd appreciate any assistance in this matter.


Thanks...Jeff
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Old 18-05-2012, 08:46   #2
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Re: Fuel Polishing Questions

The one experience I have had with this setup was with much bigger engines in a trawler yacht.
The returned fuel went to a small tank, from where it was polished, pumped and tee'd off to return to each tank.
The runs to the tanks where different lengths by about 50%, and the shortest run always returned more fuel than the longer.
Friction loss in the hose.
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Old 18-05-2012, 09:05   #3
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Re: Fuel Polishing Questions

Your system is a bit confusing, which is why i think you have not had any replies.
The best practice is to have a fuel polishing system that is independenant of the fuel delivery system. The polishing system takes fuel from the bottom of the tank filters it and return it to the same tank.
The engine pickup and filtration system are separate.

Sometimes a day tank is used, and the polishing feeds fuel to this tank as well, but the principal is the same.

It sounds more like you are describing primary engine filtration rather than polishing, but perhaps I am misunderstanding your post.
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Old 18-05-2012, 09:15   #4
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Re: Fuel Polishing Questions

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Originally Posted by noelex 77 View Post
Your system is a bit confusing, which is why i think you have not had any replies.
The best practice is to have a fuel polishing system that is independenant of the fuel delivery system. The polishing system takes fuel from the bottom of the tank filters it and return it to the same tank.
The engine pickup and filtration system are separate.

Sometimes a day tank is used, and the polishing feeds fuel to this tank, but the principal is the same.

--which was the owners thinking in my reference, hence polishing on the return side..
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Old 19-05-2012, 22:29   #5
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Re: Fuel Polishing Questions

Your fuel polishing system should not have anything to do with your engine fuel system. As the post above states. Just my two cents, Mike.
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Old 21-05-2012, 10:19   #6
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Re: Fuel Polishing Questions

Perhaps I am wrong in the layout, but what I was trying to do was create a filtering system that would use one filter and pump for both tanks; filters and pumps are expensive. I also thought that the pump could serve as a backup if one of the engine pumps ever failed. I'll have to rethink my setup...

Thanks to all who responded.
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Old 21-05-2012, 10:28   #7
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Re: Fuel Polishing Questions

can you mount it some where amidships? either way you could just use two 3 way valves and polish one tank at a time. The longest run might be less efficient but should work with a good pump like a Walbro etc.
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Old 21-05-2012, 10:50   #8
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Re: Fuel Polishing Questions

Quote:
Originally Posted by Cap View Post
Perhaps I am wrong in the layout, but what I was trying to do was create a filtering system that would use one filter and pump for both tanks; filters and pumps are expensive. I also thought that the pump could serve as a backup if one of the engine pumps ever failed. I'll have to rethink my setup...

Thanks to all who responded.
Filters and pumps are expensive, but one of the things us monohull sailors envy is the redundancy that the two engines provide in a catermaran. Make sure you don't loose this. Each engine will have a filter installed on the block. This is known as the secondary fuel filter. In addition each engine should have it's own primary fuel filter.
The polishing filter is separate. It's fine to use one polishing filter for 2 tanks, it just needs a bit more plumbing. The polishing fuel filter pump can be used to feed fuel to the engine if the lift pump fails. This needs more plumbing and if you want to do this for both engines you may be better with 2 pumps.
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Old 21-05-2012, 13:28   #9
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Re: Fuel Polishing Questions

I picked up the habit of getting my fuel from the bottom of the tank 45 or so years ago. When my dad would buy a new boat the first thing he did was change the fuel pickup to the bottom his reasoning was to get the crud out before it became a problem. I would much rather have a fuel problem in the vicinity of the fuel dock from a bad load of fuel than coming in the pass on a stormy windy night. Back then they did not know about fuel polishing etc. I don’t ever remember having a fuel problem back then. Just my two cents, Mike.
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Old 21-05-2012, 13:35   #10
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Re: Fuel Polishing Questions

Fuel was different "back then".
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Old 23-05-2012, 13:32   #11
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Re: Fuel Polishing Questions

Cheechako,

I would like to mount amidship, but alas, no where to mount it! I am using a Walbro pump, so at least I have that right.

Noelex, I would love to have the redundancy of 2 filters, and 2 pumps, but at the moment, I can't afford it with so many other things I need; maybe in the future I can.

I do have the secondary, on each block, as well as a primary for each. I also have what looks like automotive type inline filters, between the primary and secondary, that I was thinking of getting rid of; anyone see any reason to keep these? I would like to move the primary filters to the polishing panel as they are a B!!ch to get to in the engine compartments now, hence part of my original question of whether or not I'm creating an issue by increasing the distance the fuel must travel for the port engine.

At this point I can easily add in by-pass switches to circumvent the polishing system completely, so that's not an issue, but distances still have me questioning the setup?

I will try and post a picture of my setup so everyone can see it, and maybe I can get some suggestion on where to go from here?

Thanks to everyone that posted, I appreciate it...Jeff
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