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Old 12-03-2012, 09:33 PM   #1
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Diesel Tank Draw Off

Diesel tanks usually have their draw offs in the form of a dip tube / pipe which enters through the top of the tank and goes to within 1" of the bottom. This is the recommended way I guess (required way for gasoline)

However when I replaced my tank 10 years ago, I put the draw valve at the lowest point on the theory that I wanted the sludge/water in a prefilter not caked on the bottom of the tank as happened with the old tank. I have never had a problem in the 10 years since this was done.

I need to have the tanks cleaned in my Willard and I am thinking of repiping them in the same way afterwards.

What say you all?
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Old 12-03-2012, 09:50 PM   #2
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That's how mine were plumbed. they lasted 60 years that way. I rebuilt two of them and did it the same way. I see no problems with it.
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Old 12-03-2012, 10:13 PM   #3
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Brooksie,
That's how I ordered it when I replaced my tanks but no one listened to me and by the time I got down from Alaska it was all done... wrong.

With the syphon tube to 1" (aprox) from the bottom rusting and sludging is absolutely guaranteed .... how stupid.

What I ordered was a take off tube emerging from the BOTTOM of the tank at the lowest point. I got one on the side of the tank 1/3rd of the way fwd of the aft end of the tank. Now I need to rig a temporary suction tube w a special dedicated pump to evacuate water & sludge from my tanks about every 3 months. Don't let this happen to you.

The reason (of course) for the vertical suction tube is to prevent accidentally snagging the fuel hose and winding up w all the fuel from that tank in the bilge. It could possibly happen but I would/will take that chance.
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Old 12-03-2012, 10:21 PM   #4
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Many diesel tanks I'm familiar with and the ones on my boat have draw points from the bottom of the tank. I dislike top draw but many tank manufacturers are getting stubbon to do it only from the top nowadays....
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Old 12-03-2012, 10:22 PM   #5
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Spy's tanks are plumbed bottom draw for the last 32 years. I've borescoped them twice. Nice and clean.

A dip tube would make a lot of sense for primary suction. But, (a big but) ONLY if you had a low point drain.
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Old 12-03-2012, 10:36 PM   #6
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Thanks for the feedback. Made the single tank myself so I did not have any resistance to doing it that way.

Now for a second question: I had planned to slope the lines (from the bottom of the two wing tanks) slightly down to a central prefilter & leave both valves open to equalize levels returning to both tanks also. Theory being that the lines sloped down to the prefilter will cause some of the air bubbles (from rolling when the tanks are low) to roll back up to the tanks instead of into the prefilter.

Again, sense or nonsense?
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Old 12-03-2012, 10:41 PM   #7
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Wow, been thinking about that one for a while. It kinda makes since theoretically but I don't know if you would have that much bubble action unless your running out of fuel.
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Old 12-04-2012, 04:18 AM   #8
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Quote:
Originally Posted by Brooksie View Post
Thanks for the feedback. Made the single tank myself so I did not have any resistance to doing it that way.
Now for a second question: I had planned to slope the lines (from the bottom of the two wing tanks) slightly down to a central prefilter & leave both valves open to equalize levels returning to both tanks also. Theory being that the lines sloped down to the prefilter will cause some of the air bubbles (from rolling when the tanks are low) to roll back up to the tanks instead of into the prefilter. Again, sense or nonsense?
This is precisely how my tanks are set up, and it works perfectly. My filters last years and years, and I get about 1 desertspoonful of water per year out of the primary filter separator.
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Old 12-04-2012, 05:20 AM   #9
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What say you all?
We are really lucky with regards to the fuel system on our boat. The previous owner of our boat replaced the boat's original tanks and hoses the year before we bought it. The system he had fabricated and installed has four 85 gallon sadle tanks (two opposing pairs) and a 60 gallon day tank in the bilge between the engines.

The four saddle tanks all drain fom their lowest points and are used to fill the day tank via gravity and manual valves. The day tank feeds the engines and generator from its lowest point. So no pickup tubes in any tanks.

The engines can be valved to pull from either of the saddle tanks on their side of the boat through the same lowest-point feeds that are used to transfer fuel to the day tank. So no water or sludge accumulation in a tank is possible because when a tank is drawn down to empty it is dry as a bone inside.

Each saddle tank has a sight gauge and the day tank has an electric level sender to a fuel gauge on the instrument panel at the lower helm station.

The boats tanks and valve setup has let us develop a fuel management system that minimizes the time fuel sits on the boat--- the longest any fuel can sit on the boat before being used is about three months.

As far as we're concerned a fuel system with no pickup tubes, all fuel feeds are from the tanks' lowest points, and everything including fuel filtration is done by gravity is the way to go if it's at all possible to put such a system in the boat.
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Old 12-04-2012, 07:10 AM   #10
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A dip tube would make a lot of sense for primary suction. But, (a big but) ONLY if you had a low point drain.

That is the US Navy way. thanks Taxpayers!

Bottom drain under an internal shelf , to keep un-drained sludge from mixing, and a top draw for the engine.
Monel tank , , bottom drained at the start of each season .

No problems , since I relocated the deck fills to under an 8 inch deck screw out cover

Water over the deck or rainwater can not go into a loose fill cap .Or find its way in to the fuel tank from a bad O ring.
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Old 12-04-2012, 10:11 AM   #11
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A sump and bottom drain or a fuel feed at the bottom would be great, but many tanks are flat on the bottom so they can be installed on a flat surface. A sump or bottom drain or pickup would require the tanks to be mounted above that surface somehow.

I remember many, many years ago, cars had drains on the bottom of their fuel tanks.
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Old 12-04-2012, 08:21 PM   #12
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I tend to go no sumps and no holes on the sides or bottom of the tanks and a slight grade on the tank top. Where possible I fold the tank sides out of the bottom plate to reduce the welds. I try to keep water out of the tank, by using a water block fill filter and when possible I only fill the day tank, transferring the fuel to the storage tanks with the onboard transfer/filter system. Only returning hot fuel to the day tank will help reduce the amount of water drawn in through the vents and reduce the plumbing.
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Old 12-04-2012, 08:26 PM   #13
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I'd be curious to know what the new build boat regs for fuel draw lines are to satisfy Europe, Australia, ABYC (huh), insurance, EPA (egads) etc. These regs are not new. The bottom line I have heard for years, to remain legal, is you don't want your tanks to have a way to drain via bilge pump into the water in the event of a fuel line failure. Fines are pretty stiff for diesel spills occurring due to malfeasance.

Top mounted suction lines seem to be pretty much the standard in the better designed boats built during the past 20 years or more. My 4 tanks have bottom drains, with valves and plugs to prevent an inadvertent drain event. The sight tubes are valved as well. This is pretty standard stuff it seems.
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Old 12-04-2012, 08:34 PM   #14
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The four new saddle tanks the PO installed in our boat sit on heavy wood frames that support the tanks above the sloping-down bottom of the boat. The tanks themselves are flat on the top but have bottoms that are slightly sloped inboard. But being up on their frames provides plenty of space and clearance for the gravity feeds. Each saddle tank has a sight gauge but there is only a shutoff valve on each gauge at the bottom, which is not a good idea. There should be shutoff valves both top and bottom.
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Old 12-04-2012, 09:54 PM   #15
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A sump and bottom drain or a fuel feed at the bottom would be great, but many tanks are flat on the bottom so they can be installed on a flat surface. A sump or bottom drain or pickup would require the tanks to be mounted above that surface somehow.
They could be mounted with one end slightly overhanging the flat surface to allow for a small sump for the water and crud to collect. May not be easy but if I renew my tanks (never I hope!) a sump will definitely feature.
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Old 12-04-2012, 10:27 PM   #16
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When I replaced the steel tank in my boat, I had a sump installed in the bottom of the new one, centered port to starboard and 1" off the stern wall. The sump is 4" in diameter by 4" deep and hangs over the hollow keel. I set the draw tube 1/2" off the bottom of the sump; the return line dumps over the sump; the fuel tank fill is directly over the sump. Everything flows to the back of the tank when the boat is up on plane, and any water or debris will eventually fall into the sump and get sucked into the Racor 1000 separator. Because the fill is directly over the sump, I could vacuum the sump if necessary. When the fuel is low in the tank, I can also lower a fiber optic light into the tank to check the sump for debris. 10 years later, the inside of the tank is as shiny and clean as the day it was made. While I don't plan to run close on fuel, I saw no reason to have 10% of a 10" tall tank unusable because the draw tube was 1" off the bottom. If I stayed up on plane, in an emergency I could probably suck the tank dry.

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Old 12-04-2012, 11:00 PM   #17
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Azimut yachts had bottom feed and sight gauges until the mid 90s that I know of...I don't think anyone who knows ANYTHING about boats gives a hoot about top feed safety on diesel boats...just too many other things can go wrong to worry about that item.
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Old 12-05-2012, 07:00 AM   #18
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Azimut yachts had bottom feed and sight gauges until the mid 90s that I know of...I don't think anyone who knows ANYTHING about boats gives a hoot about top feed safety on diesel boats...just too many other things can go wrong to worry about that item.
Guess I don't see the disadvantage to a top feed tank. As to sight gauges, nothing wrong with them, just prefer to stick my tank as it's one less thing to have problems with (can't fail if it's not there). Obviously some tanks can't be sticked because of the routing of the fill hose, and for them sight gauges are fine.

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Old 12-05-2012, 07:28 AM   #19
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psneeld said:

"I don't think anyone who knows ANYTHING about boats gives a hoot about top feed safety on diesel boats..."

I assume this is in USCG regs too?
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Old 12-05-2012, 08:08 AM   #20
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psneeld said:

"I don't think anyone who knows ANYTHING about boats gives a hoot about top feed safety on diesel boats..."

I assume this is in USCG regs too?
Correct...it's a requirement for gas boats but not diesel boats...can't say for sure about inspected vessels but as I posted I know of rec boats with bottom feed and sight glasses that the USCG has no problems with.
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