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Old 06-07-2016, 11:34 AM   #41
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Originally Posted by sunchaser View Post

OCD and others have nailed it - buy boat diesel from the right seller, use it and keep your filter changes up to date. BTW, buying from the back end of Joe's clapped out delivery truck introduces a few new questions.
Yes it does, but some don't always have a choice between good times and good locations for purchasing. Easy for those who only cruise populous boating heavy cruising grounds and only in peak season.
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Old 06-07-2016, 04:31 PM   #42
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I think the best defense against bad fuel is to have some sort of fuel segregation policy where possible given the boats tankage. Purchased fuel goes in one place, and fuel to burn goes someplace else, and never the two shall mix - except via transfer through a filter and water separator. You can call it a day tank, but I think there are other ways to accomplish the same thing without a specific day tank. But it's all highly dependent on your boats configuration.

But segregating purchased fuel and burn fuel doesn't absolve you of the need to monitor and keep the purchased fuel tank clean, and so brings us right back where we started. But al least bit keeps the crap away from the engine, which I think is priority one!
Well said. I certainly hope you're right because this is the approach I intend to take. We have a third, aft, 200-gallon tank (that had better last more than a day) that I plan to draw from exclusively while underway. The fuel that goes into it will be filtered each day. The tank is relatively easy to inspect, draws from a sump at the very lowest point and whatever doesn't get used, will get pumped back into the storage tanks rather than sitting for weeks at a time.
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Old 06-07-2016, 05:02 PM   #43
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I suspect Joes old ratty truck delivers cleaner fresher fuel than the local marina where it sits for a while.
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Old 06-08-2016, 12:04 AM   #44
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Fuel Polishing onboard

We have the ESI system. All pickups from the bottom of the tanks. We typically move fuel from one tank to another, polishing fuel in the process. When refuelling we transfer the remaining fuel to the forward tanks and fill the aft ones. We typically drawn from the forward starboard tank.

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Quote:
Originally Posted by sunchaser View Post
So here is the question - is a setup of off engine filters, valves, vacuum gauges and in some cases manufacturer decals really polishing or just good marketing?

I agree. It's pretty impressive but I don't think I'd pay the big bucks to install one.

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Old 06-08-2016, 01:50 AM   #45
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Nice setup JD. You gave it some thought and put it together to address the specifics of your vessel.

Can you dip your tanks to assess what if anything is lurking on the bottom? Shouldn't be anything I'd guess with your setup.
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Old 06-08-2016, 06:51 AM   #46
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"The tank is relatively easy to inspect, draws from a sump at the very lowest point"

The usual draw from the sump at "the very lowest point" is to remove water and crap in the fuel that will settle there.

6 inches higher has a better chance of only picking up clean fuel.

IF all fuel tanks were built with good sumps , (that were serviced) there would be almost no need for fuel polishing.

A box for fuel instead of a marine fuel tank is cheaper to buy/install for the boat assembler..
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Old 06-08-2016, 07:01 AM   #47
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The usual draw from the sump at "the very lowest point" is to remove water and crap in the fuel that will settle there.

6 inches higher has a better chance of only picking up clean fuel.
Agree -- for storage tanks. Since this is a day tank where filtered fuel will only be put in a day or so before it's used, and the tank can be fully emptied afterward, there should be no opportunity for crud to form. We'll see how it works.
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Old 06-08-2016, 08:17 AM   #48
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Just because a system has an extra filter and a pump doesn't make it an effective polishing system. Some key features that do help are:

- fuel pickup from the very bottom of the tank. This is where water and other guck will settle, and if you system can't pick it up then it's doing no good. Dip tube pickups are typically designed to have exactly the opposite characteristics and intentionally pick up from a point above the guck. Most of the Nordhavn I have seen work this was and as such are advertised as transfer systems, not polishing systems.

- a fuel return location and fuel flow rate that will actually cause some agitation in the tank. This will stir up settled gunk so it can be sucked through the polishing filter. Most builtin polishers do not accomplish this as all since they use the normal top of tank return port. But this capability is really only important to rectify a long accumulation of gunk, and if you have such a situation, a polishing service should have the necessary equipment with return hoses that can be directed to different areas in the tank.

Because of all this, I seriously doubt that most boat polishing systems provide any real benefit that is not also provided by your main filters and the engine constantly circulating fuel. That will remove suspended impurities just as well as a polisher using the same pickup and return ports on the tank.

I think the best defense against bad fuel is to have some sort of fuel segregation policy where possible given the boats tankage. Purchased fuel goes in one place, and fuel to burn goes someplace else, and never the two shall mix - except via transfer through a filter and water separator. You can call it a day tank, but I think there are other ways to accomplish the same thing without a specific day tank. But it's all highly dependent on your boats configuration.

But segregating purchased fuel and burn fuel doesn't absolve you of the need to monitor and keep the purchased fuel tank clean, and so brings us right back where we started. But al least bit keeps the crap away from the engine, which I think is priority one!
I rarely polish fuel unless the tank level is down to the last 20 or 30 gallons and we're out in a seaway. We've burned thousands and thousands of gallons but probably have collected a total of a teaspoon of gunk in the Racor bowls over the years. The rest of it is trapped by the filters. If you burn your fuel load in a couple of months you probably aren't going to benefit from a polishing system. If you carry it for a couple of years or refuel from 55 gallon drums someplace you will, IMO.
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Old 06-08-2016, 11:13 AM   #49
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Fuel Polishing onboard

Quote:
Originally Posted by sunchaser View Post
Nice setup JD. You gave it some thought and put it together to address the specifics of your vessel.

Can you dip your tanks to assess what if anything is lurking on the bottom? Shouldn't be anything I'd guess with your setup.
Ted: The PO put this system in after he replaced the tanks. I have inspection ports but I haven't dipped the tanks at all.

One approach to "fuel polishing" would be to move most of the fuel to other tanks and when the tank is near empty, set the "return" valve to have the fuel return back again to the tank being polished, thereby creating agitation to the remaining contents in the tank.

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Old 06-09-2016, 06:04 AM   #50
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"have the fuel return back again to the tank being polished, thereby creating agitation to the remaining contents in the tank."

Even 30 GPH of a Detroit being returned will not agitate the tank as much as falling off a wave, just once.

Fuel polishing may be great fun , but it does not clean a fuel tank.
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Old 06-09-2016, 07:27 AM   #51
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My particular 'fuel polishing' system involves a Perkins 8 GPH fuel return line sucking from/ returning to one tank at a time. One day the port, The other day the stbd. Keeping fuel onboard to a conservative minimum (anticipating Fuel needed.) Last summer I used the boat 30 gallons/hours. So it pumped 240 gallons of fuel. I only have 50 gallons aboard. So the fuel was filtered(polished) to 2 microns approximately 4.5 times.

Agreed that an afternoon sloshing around in a seaway does more to 'loosen up' in tank crud than any polishing system.

Probably the most important tool in the box to figure out fuel tank/filter sludge status is a fuel vacuum gauge.

On my boat the engine runs normally around 2 lbs vac.

When the fuel line shows 7to 8 lbs vac the engine stumbles and hunts.

At 10 it shuts down. Ask me how I know this......

I learned this in delivery in the middle of Lake Erie.

Two summers ago I went through around 18 fuel filters after I bought the boat. The fuel ( 150gl) had been onboard for around 3 years. And I burned about 130 gallons on delivery.

Now two years later the tanks are clean. And I change filters once a year.
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