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Old 07-11-2015, 08:50 AM   #1
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Series fuel tanks?

I read about people installing several connected smaller tanks when the original large tank fails.

How to several smaller tanks get connected? Where does fuel pick up tube go? Are they both filled from one inlet?
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Old 07-11-2015, 09:26 AM   #2
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for me..each has a top pick up as they are poly and go to a valved manifold.


each could just be valved into a long fuel line.


returns the same..on a Lehman 120 the return is so low I plumbed it back to a manifold then into the beginning of the fuel manifold.
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Old 07-11-2015, 09:31 AM   #3
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We have 5 tanks and 5 fuel fill inlets . One tank is just for the genny . One tank is large and not plumed to engine just to a fuel polisher . The other three tanks are plumbed to engine with several valves and hose . Each tank has its on return but the vents are plumbed together to one vent . It's not fancy by no means but it works . One of the items on our list to do is clean this up and install nice labeled manifold . The tanks are aluminum and fairly new .
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Old 07-11-2015, 10:07 AM   #4
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Four tanks, all plumbed to separate manifolds for supply and return. Allows transfer between tanks, very useful both for weight distribution and emptying a tank prior to filling. The pump used for transfers is the fuel polishing system.

Each tank has a separate 2" fill and a 5/8" vent.
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Old 07-11-2015, 10:41 AM   #5
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So the replacement tanks are used as separate tanks, each with in and out valves, not all connected together through some large hose at bottom?
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Old 07-11-2015, 12:24 PM   #6
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So the replacement tanks are used as separate tanks, each with in and out valves, not all connected together through some large hose at bottom?
That is the situation, by design, on Bay Pelican.
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Old 07-11-2015, 01:04 PM   #7
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If you have bottom taps on the tanks, you can tie them all together at the bottom and gravity will equalize. You can't do that with top taps as air pockets will prevent natural equalizing.

With bottom ties, you can fill through one, but it will be a long wait for them to equalize, making it hard to get all the way full.

I don't think poly tanks makers like using bottom taps, as the plastic deforms with NPT threads and over time it may leak down there. Probably forced to use top taps for everything, then each tank will need its own fill.
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Old 07-11-2015, 03:12 PM   #8
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My boat has port and starboard fuel tanks plumbed like Ski said with bottom taps that flow to a common header and feed the engine. The header keeps the level equalized and the return is to just one tank. But as he noted you have to fill each one separately as it takes a long while to equalize. These are SS tanks.


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Old 07-12-2015, 07:24 AM   #9
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The joy of multiple tanks is most of them can be empty , not growing bugs.

When you need the 1,000- 2500- 4000 mile range , all can be filled
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Old 07-12-2015, 08:46 AM   #10
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If the fuel draws from two tanks wont one go dry and stop the engines before the second is dry? I guess you draw from the aft tank so that any bow rise will flow fuel aft.
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Old 07-12-2015, 10:40 AM   #11
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valved.
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Old 07-12-2015, 10:55 AM   #12
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That's what I figured so things are a bit more complicated with split tanks.
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Old 07-12-2015, 11:05 AM   #13
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not really complicated....just needs a tiny bit of attention when you need to switch over...all valves closed except the feed/return lines to the "current" tank.


Most vessels need some form of fuel tank management, tiny tanks just need it more often.
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Old 07-12-2015, 11:15 AM   #14
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Quote:
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not really complicated....just needs a tiny bit of attention when you need to switch over...all valves closed except the feed/return lines to the "current" tank.


Most vessels need some form of fuel tank management, tiny tanks just need it more often.
We have 2 tanks and they have valves for the supplies and returns. Pretty easy and we need to balance the boat. We have found that when both tanks are equal that Hobo lists to starboard so that tank gets drawn down first. I was on a delivery a few weeks ago with a bow and stern tank. Drawing down the bow tank first helped with the performance in a good way.
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Old 07-12-2015, 01:03 PM   #15
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We have 2 tanks and they have valves for the supplies and returns. Pretty easy and we need to balance the boat. We have found that when both tanks are equal that Hobo lists to starboard so that tank gets drawn down first.
Same with my (small) boat....60 Gallons fuel and 30 Gallons water per side.
My homemade polsher/transfer system allows me to keep her relatively level under all conditions with a bit of fuel transfer ..
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Old 07-13-2015, 06:50 AM   #16
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With our launch . fuel refilling was not expected to be a hassle , so 100G per side is it.

The Flow Scan allows us to keep track of the burn each day , and a simple rotating valve switches the fuel supply and return tank at the same time.

With 10G remaining in each tank its time to visit the fuel stop.

At 3gph for 7K , 180G is a lot of ditch crawling near 500 NM (600 with statute ditch miles)

Fuel is used to cool the fuel pump and injectors (DD 6-71) so 10G is about our chosen limit.
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Old 07-13-2015, 07:20 AM   #17
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Two tanks on my boat. It's now plumbed where fuel is only drawn from the starboard tank. There is a fuel polisher that allows fuel to be drawn from either tank and returned to either tank. The plan is to only fill through the port tank and then transfer as need through the polisher to the starboard tank so that all fuel is polished first. In the event of the polisher pump failing the valves on the polisher manifold can both be opened allowing the tanks to equalize (tank outlets are at the bottom of the tanks). My boat has a port list. So plan to use fuel distribution to correct the list.

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Old 07-13-2015, 12:17 PM   #18
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Our DF has four tanks, four fills, valved draw and return manifold and transfer pump. Even though the tanks have equalizing lines, they are not used. Sight tubes (calibrated) are on each of 4 tanks. Pretty much a standard design on hundreds of DFs for the past 25 or more years. AND sloping tank bottoms to minimize crud accumulation. God bless Art!
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Old 07-13-2015, 03:33 PM   #19
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The Coot has four 79-gallon fuel tanks located below the deck. Two manifolds, one for "to engine" and one for "from engine" control tank selection. Drawing from one tank at a time (although drawing and returning can be made in any combination), I need to switch between starboard and port tanks every six to eight operating hours to maintain trim. The two 100-gallon water tanks are located port and starboard also, but the plumbing allows drawing from both tanks simultaneously so there is no need to manually equalize.
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Old 07-13-2015, 04:28 PM   #20
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The three original tanks in our boat were replaced by the previous owner 18 years go with five smaller tanks. This did not require the removal of the engines although I suspect the transmissions had to be removed. The original tanks were cut up in place and the pieces removed.

In place of the original three 150 gallon iron tanks there are two 85 gallon saddle tanks on each side of the boat and a 60 gallon day tank in the bilge just aft of the engines. All five tanks feed from their lowest points via gravity. There are no pickup tubes and no pumps in the system other than the lift pump on each engine.

In practice, both engines and the generator feed from and return fuel to the day tank. Fuel from the saddle tanks is transferred to the day tank via gravity from the saddle tanks with manual valves. Our fuel management system has us transferring from from one opposing pair of saddle tanks into the day tank as needed until the saddle tanks are empty. We then start transferring fuel from the other oppposing pair of saddle tanks until they are about a quarter full. We then fill the two empty saddle tanks, finish emptying the two tanks we've been using and then leave them empty until the first pair are down to a quarter full, and so on.

The system is such that each engine can draw fuel from the day tank (normal setup) or from either of the two saddle tanks on the engine's side of the boat. The fuel return from each engine can be directed the same way.

The generator always uses the day tank .

Finally, fuel can be transferred between any of the saddle tanks using a separate transfer pump. This pump can also pump fuel off the boat from any tank. However we have never used this either of these capabilities in the 17 years we've owned the boat.

In summary it's a great system that is simplicity itrself but with the capability of moving fuel around if required. And because each tank feeds from its lowest point, when a tank is empty, it is totally empty.

The only negative about the whole system is the tanks are made of stainless steel. They were very well made by a speciality shop in the SFO bay area, but stainless is not the best choice for a fuel tank.
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