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Old 12-16-2011, 08:35 AM   #21
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RE: Fuel Tank Equalization

I think that a good idea before casting off is to get off the boat, step back and take a look to see if there is a list and to see if she has any trim. If she does then move a few things around. A little trim to the stern is ok, meaning a degree or two, but a list can be dangerous. If you are listing to port and taking wind and waves to the starboard bow this weather can cause the list to port to be exaggerated. I think that the recreational trawlers are somewhat proportional in their design to their larger commercial sisters. Everything may be smaller in scale, but wouldn't the characteristics be similiar? I don't know for sure but it seems to make sense. Plus, when sailing, I do not want anything going on that I am not in control of and not sure of, meaning allowing fluids to move from on place to another freely and not knowing how much weight that is and when it is makes me nervous. At roughly eight pounds a gallon for diesel seems like it can sure get heavy in a spot quickly. Maybe not, I'm just trying to get a handle on the idea.
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Old 12-16-2011, 08:56 AM   #22
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RE: Fuel Tank Equalization

When I first got my boat, I filtered all the fuel. Having approx 1/2 tanks full, I filtered one to the other, then all back to the empty tank. So my*port tank was full and*starboard empty. (180 gal tanks each side)

The list was only a few degrees, I would estimate 5 maybe 10.

It took about 4 hours of "partying" with as many on the starboard side to get the tanks even again.
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Old 12-16-2011, 09:41 AM   #23
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RE: Fuel Tank Equalization

Most of our boats have cross over pipes to the tanks with valves to cut them off if needed. So how many have ANY first hand knowledge, not I heard it from someones cousin that heard it in the local grocery store check out line, of one of our types of vessels that capsized from cross overs in the fuel tanks. I think we have so many other things to be concerned with as boat owners that we don't need to sit around and worry about things that are never going to happen. I have had one tank full and the other empty, even while under way. There is no more difference than if two people are standing on one side of the boat as far as the listing. Chuck
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Old 12-16-2011, 10:00 AM   #24
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RE: Fuel Tank Equalization

A few thoughts:

I switch my tanks but most of the time I do'nt do it until I notice a slight list so some undesirable listing happens. Fly stuff in my opinion but it does happen. But I like to have the control. But if a list is caused by everybody going to the port rail or worse the cross-over system will allow fuel to flow over to the port side and cause more list. That's the main reason I do'nt like cross-over lines as I loose some control. And I've always been fussy about listing especially under way. I've never used cross-over tubes but one could probably boat for 100 years w then and not have a problem.*
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Old 12-16-2011, 06:39 PM   #25
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RE: Fuel Tank Equalization

True, we're not as complicated,*don't have ballast tanks*and like someone pointed out, fuel tanks are ballast, but are most often at or below the waterline.**Empty tanks on one side might cause a slight list and could effect handling in the wrong conditions.**But*IMHO, the capsize danger for recreational boaters*is more likely going to be from operator negligence,*too many people on board, too*much above deck load, running with too much sail, combined with high seas*or bad weather*and inexperience/poor handling skills which can lead to disaster.**

A guy at our marina was loading 80 lb bags of Quickrete on his 27 foot boat to transport*to his cabin on Decator Island.* He had 100 bags and was going to do it in one trip he thought.**Other marina patrons*were*encouraging him to split it up into at least four loads.* After insisting he could do it and had done it before, he got around 50 bags on before the boat began leaning on the dock.* If he had untied the lines, it would have rolled.**He ended up taking half of it off and made*three or four trips.* It's called the Forrest Gump syndrome, "Stupid is as stupid does!!"**

*
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Old 12-16-2011, 06:47 PM   #26
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RE: Fuel Tank Equalization

What?* Me list?

*
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Old 12-17-2011, 12:18 AM   #27
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RE: Fuel Tank Equalization

I understand it is good practice with twin engines to normally feed (and return) each engine from a different tank, so that if one tank becomes contaminated you don`t risk losing both engines. If that is right ,won`t equalization effectively combine the two tanks, defeating the practice?

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Old 12-17-2011, 03:30 AM   #28
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RE: Fuel Tank Equalization

My boat's fuel tank set-up is a lesson in KISS. They are able to be closed off by a tap and each exit point, but I leave them open all the time, and the lines meet in the middle as it were, then feed the engine, with the the excess fuel return just feeding back to the primary filter. Beautifully simple, and as they drain from the bottom, no crud builds up and I release a teaspoonful of water from the primary filter bottom bowl once a year. It means they are always level, and I can fill from either side, and they will ultimately level out then as well, as I never top right up normally. If I am I add to both sides to save time waiting for the leveling to occur.
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Old 12-17-2011, 04:30 AM   #29
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Fuel Tank Equalization

Bruce-

True in theory..but most people I've talked to about this ..at least here in the States...they have never nor heard of anyone where it would have mattered.* Mostly because you have to fill only one side from one source to prevent contaminating both sides...which people almost never do.* The good news is* that marinas here on the East Coast in busy areas are almost never the problem.


-- Edited by psneeld on Saturday 17th of December 2011 05:30:41 AM
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Old 12-26-2011, 11:40 AM   #30
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RE: Fuel Tank Equalization

Actually both my engines and the generator pull from the center-line tank. Fuel from the saddle tanks gravity feed into that tank. I have shut-off valves on both saddle tanks.
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Old 12-26-2011, 04:31 PM   #31
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RE: Fuel Tank Equalization

Our system is similar to MTs. There is a pair of saddle tanks on each side of the engine room. These gravity feed from their lowest points via manual valves to a 60 gallon day tank in the bilge between the engines. Both engines and the generator normally feed from this day tank and the fuel returns go to the day tank.

However each engine is capable of being fed directly from one of the two saddle tanks on its side of the boat and the fuel returns can be valved to return to a saddle tank. But we have never in 13 years of using the boat ever done anything but feed everything from the day tank and return everything to the day tank.
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Old 12-26-2011, 07:05 PM   #32
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Fuel Tank Equalization

We designed the same configuration with a couple of minor differences.

We have two 675 gallon saddle tanks that feed a 400 gallon center line bilge tank. The saddles gravity feed the center and all engines draw from the center. However the return goes to the starboard saddle. This accomplishes two things; one is that we want the center tank to stay coolest, (the center tank is not in the engine room) cool fuel is more efficient. By having the return go to the saddle it has a chance to cool befor being used again. The second reason for not sending the return to the center tank is with the center tank being gravity fed, it is always full. Adding return fuel to this is just pushing fuel back up into the saddle tanks. The return fuel should be top fed into one or both saddles.

A minifold should allow you to reconfigure this to feed all engines from any individual tank. Ideally you should be able to gravity balance the saddles independent of the center tank or through it.

Lastly the polishing system should allow you to filter between any of the three.

All IMHO.

-- Edited by Just Bob on Monday 26th of December 2011 08:06:37 PM
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Old 12-26-2011, 08:43 PM   #33
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RE: Fuel Tank Equalization

Quote:
Just Bob wrote:
cool fuel is more efficient.
Your engine burns fuel by weight, its efficiency has no relationship to the fuel temperature.

It can't even begin to contribute anything to the process until its temperature is above about 450*F.

The reason fuel coolers exist is to ensure that the fuel temperature is below its flash point while being pumped around the engine room and stays below that temperature until it reaches the fuel injectors. The other reason cool fuel is nice is because it retains the viscosity needed to prevent undue wear and deposits on the fuel injection components.
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Old 12-27-2011, 04:05 PM   #34
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RE: Fuel Tank Equalization

To the previous comment I would have to add:

Fuel being returned to the tank is the unused fuel from the injectors, remember that for the fuel to be used in the injector it has to be compressed to around 30,000 PSI. * Compressing a non-compressible substance creates large amounts of heat. This heated fuel is what is being returned to your tank.

The reason you*want to have the coolest possible fuel before going into the fuel pump is for the heaviest densest possible amount of fuel to be compressed into the injector lines. The colder the fuel before the pump the colder it will come out after being compressed.*

Thermal dynamics of the fuel come into play. *Say there is a 50*F temp rise during the fuel compression cycle and your fuel is at 60*F, the fuel now going into the injectors is 110*F. *Now a gallon fuel at 60*F takes up say 0.75cuft and that same gallon of fuel at 110*F will take up 0.83cuft. *This means you have a lighter less dense fuel taking up space where you could possibly get a denser fuel to occupy and have more power per cu.ft.

It doesn't take much research to see this is a debatable subject but I would still stand by my opinion that cool fuel is more efficient.

Thank you for your addition though, much of what you say is correct as well.
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Old 12-27-2011, 04:48 PM   #35
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Fuel Tank Equalization

*
Quote:
Just Bob wrote:It doesn't take much research to see this is a debatable subject but I would still stand by my opinion that cool fuel is more efficient.
It doesn't take any at all to see that there is nothing to debate.

Heat transported by the return fuel comes from the injector body which is heated by combustion.

Any heat created by pumping is so far down in the "noise" as to be insignificant.

The fuel does not gain or lose "efficiency" with temperature. Fuel provides a certain heating value or number of BTUs per unit of weight.

Any reduction in weight per unit of volume admitted to the injector pump cylinder caused by increased temperature is compensated for automatically by the governor admitting more volume to inject the weight of fuel required to maintain the selected rpm.

Until the governor is operating at the fuel limit stop, you, the operator will not even know anything has changed. At that point the engine will be unable to maintain the same rpm it would with cold fuel but since your engine rarely, if ever reaches the fuel limit except under aggessive acceleration that point will probably never be seen unless you routinely shove the throttles forward to make large clouds of black smoke.

The fuel* heating value does not change ... its "efficiency" certainly doesn't - whatever efficiency means in your context.

Considering that fuel cannot contribute anything at all to the process until it reaches autoignition temperature - around 450F, by your understanding there would be little point in even using it. The energy required to raise the fuel charge to that level is subtracted from the heat of compression so if the fuel could be heated to 449F before being injected for free and without other consequences, the engine would actually be more efficient.

You are confusing grapes and grapefruit.

(edited for clarity)


-- Edited by RickB on Tuesday 27th of December 2011 06:31:08 PM
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Old 12-27-2011, 09:57 PM   #36
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RE: Fuel Tank Equalization

Best you return to the tank you are drawing from, that way you never have to worry about an inadvertent fuel dump costing many eco damage $$$.

Having worked with diesel equipment in Yuma AZ, I can tell you hot fuel is not an issue. Having worked with diesel engines in the far north, I can tell you cold fuel is a heck of a problem.

Fuel polishing discussion again - won't hurt but will it really help on a*well cared for vessel? Just get a top notch filter setup, turn your fuel over*and buy clean fuel*- you'll sleep soundly.
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