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Old 21-11-2017, 15:36   #1
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Auxillary diesel tank install

I am currently installing 2 approx 300l flexible auxillary diesel tanks, in the bilges of my cat. 2 methods of connection, 1. With 2 3way ball valves to each tank and change both supply and return to each engine. 2. Small inline diesel pump in outlet of aux tank and pump into an existing spare 1/2" inlet thru a ball valve on top of main tank, the aux tanks will only be used occasionally for longer passages eg crossing Bass Straight. Any thoughts?
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Old 21-11-2017, 16:06   #2
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Re: Auxillary diesel tank install

It sounds like you have an opportunity to create an auxiliary fuel supply which can provide a redundant back up as well. Can you set up your auxiliary tanks to provide fuel directly to their engine through their own filters? This would give you an alternate fuel supply if your main tanks are compromised.
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Old 21-11-2017, 16:51   #3
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Re: Auxillary diesel tank install

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Originally Posted by Lunita View Post
It sounds like you have an opportunity to create an auxiliary fuel supply which can provide a redundant back up as well. Can you set up your auxiliary tanks to provide fuel directly to their engine through their own filters? This would give you an alternate fuel supply if your main tanks are compromised.
I already have a back up system thru gen set tank. The aux bladders will be rarely used, and probably removed for most of the time.
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Old 22-11-2017, 01:10   #4
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Re: Auxillary diesel tank install

No more ideas?
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Old 22-11-2017, 01:18   #5
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Re: Auxillary diesel tank install

Sort of on topic ...

I installed a day tank when fitting a new engine not so long ago - Looks more complicated than it is but with a few valves I have the option of pumping to or from canisters and through filters so if dirty fuel does get into the main tank it can be filtered before getting to the day tank. Triangles are three way tee valves, one of two inputs to an output.

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Old 22-11-2017, 08:35   #6
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Re: Auxillary diesel tank install

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Originally Posted by conachair View Post
Sort of on topic ...

I installed a day tank when fitting a new engine not so long ago - Looks more complicated than it is but with a few valves I have the option of pumping to or from canisters and through filters so if dirty fuel does get into the main tank it can be filtered before getting to the day tank. Triangles are three way tee valves, one of two inputs to an output.

That was my idea as well. I have a Filterboss dual Racor setup, and I've considered a 10 gallon daytank, installed as a gravity feed, that has post-filter diesel and enough petcocks to make it the main tank should lift pumps fail and/or the main keel tanks become compromised. Granted, 10 gallons isn't going to get you home from the middle of the ocean, but that's not where fuel problems are likely to manifest. If you take on bad fuel, you will motor for some distance before you notice an issue, simply because the fuel (presumably good) in the existing hoses and filters will take time to be used. Hence the idea of a reservoir of "known clean" fuel: sail to the harbour and motor to the dock for the last half-mile.
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Old 22-11-2017, 09:32   #7
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Re: Auxillary diesel tank install

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Old 22-11-2017, 09:36   #8
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Re: Auxillary diesel tank install

Yes, do it, Its an excellent idea. I upgraded my fuel system with aux tanks and havent looked back. I drain my main tanks and they are thus clean, dry and uncontaminated. When I doi a long trip, I fill them, use the required fuel, drain them and run on muy aux tanks. Im so happy I did this. I never ever have contaminated fuel. Its a dream. Good luck.
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Old 22-11-2017, 12:04   #9
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Re: Auxillary diesel tank install

If you are doing this on only rare occasions don't do it. Buy Diesel fuel jugs and store them in a locker.

And do not do a 10 gallon day tank. Three reasons:

1) Your diesel fuel injection pump(s) are cooled by the fuel pumped through them. 90% of the fuel pumped is returned to the tank. A ten gallon day tank will get hot and your injection pump(s) will not be cooled properly.

2) Sooner or later you will forget to fill the day tank and your engine will stop at the worst possible time.

My story. In Trinidad my boat was rammed by a steel sailboat because the delivery skipper ran his day tank dry. While still moving through a crowded anchorage he went below to transfer fuel. Bang - a lot of damage and time lost to get it repaired.

3) Bladder tanks can chafe and leak. Do you want diesel fuel in your bilge? It may not happen for ten years but it will happen.

KISS - Keep it Super Simple - we all make mistakes. Managing multiple tanks will be a headache.

Fuel jugs are cheap, simple and with any sign of wear they are easily replaced.
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Old 22-11-2017, 13:21   #10
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Re: Auxillary diesel tank install

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Originally Posted by stormalong View Post
If you are doing this on only rare occasions don't do it. Buy Diesel fuel jugs and store them in a locker.

And do not do a 10 gallon day tank. Three reasons:

1) Your diesel fuel injection pump(s) are cooled by the fuel pumped through them. 90% of the fuel pumped is returned to the tank. A ten gallon day tank will get hot and your injection pump(s) will not be cooled properly.

2) Sooner or later you will forget to fill the day tank and your engine will stop at the worst possible time.

My story. In Trinidad my boat was rammed by a steel sailboat because the delivery skipper ran his day tank dry. While still moving through a crowded anchorage he went below to transfer fuel. Bang - a lot of damage and time lost to get it repaired.

3) Bladder tanks can chafe and leak. Do you want diesel fuel in your bilge? It may not happen for ten years but it will happen.

KISS - Keep it Super Simple - we all make mistakes. Managing multiple tanks will be a headache.

Fuel jugs are cheap, simple and with any sign of wear they are easily replaced.
Hard to fit 600l in jugs!!! The pour or siphon them to main tanks at sea.
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Old 22-11-2017, 13:26   #11
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Re: Auxillary diesel tank install

Have decided to pump from aux tanks to main tank. I will put a float switch in top of mains to control pump; to avoid forgetting to switch pump off and over filling mains. I have no intention of overcomplicating system by installing a day tank, don't have space for one anyway.
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Old 22-11-2017, 15:08   #12
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Re: Auxillary diesel tank install

Hi Bruce
I’m no expert although I do have basic Marine engine driving qualifications and have operated some very nice commercial vessels.
I am not aware of any bladders recommended for internal use, beware that you might invalidate your insurance.
There is good reason for fuel tanks being solid and properly fixed to the vessel. Crossing Bass Strait could easily throw up conditions well beyond what you anticipated.
Dave
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Old 22-11-2017, 15:19   #13
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Re: Auxillary diesel tank install

OK, I missed the part about 600 ltr. That's about 160 U.S. Gallons.

Is that a sailing Cat? If so I would guess the full throttle fuel consumption is about 4 ltr/hour. That's about 150 hours or six straight days of motoring. Reduced throttle - 2/3 hull speed would be 12 days of motoring. Does that sound about right?

I cruised for 19 years on a 44 ft monohull with about the same fuel consumption. Carried 70 U.S. Gal in main tank and a reserve of 30 Gal in jugs. Circumnavigated and never ran out of fuel.
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Old 22-11-2017, 15:30   #14
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Re: Auxillary diesel tank install

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Originally Posted by Olddave View Post
Hi Bruce
I’m no expert although I do have basic Marine engine driving qualifications and have operated some very nice commercial vessels.
I am not aware of any bladders recommended for internal use, beware that you might invalidate your insurance.
There is good reason for fuel tanks being solid and properly fixed to the vessel. Crossing Bass Strait could easily throw up conditions well beyond what you anticipated.
Dave
Fleximake, The military drop 1000l tanks from helicopters, mine are custom made to fit into bilge, probably stronger than hdpe tanks
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Old 22-11-2017, 15:36   #15
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Re: Auxillary diesel tank install

Quote:
Originally Posted by stormalong View Post
OK, I missed the part about 600 ltr. That's about 160 U.S. Gallons.

Is that a sailing Cat? If so I would guess the full throttle fuel consumption is about 4 ltr/hour. That's about 150 hours or six straight days of motoring. Reduced throttle - 2/3 hull speed would be 12 days of motoring. Does that sound about right?

I cruised for 19 years on a 44 ft monohull with about the same fuel consumption. Carried 70 U.S. Gal in main tank and a reserve of 30 Gal in jugs. Circumnavigated and never ran out of fuel.
Power cat capable of 22kts, a bit thirsty at that speed, at 12kts uses about 22 to 25 lph. Speed allows smaller weather windows to be used. I can cross Bass strait in daylight in this boat, my previous sailing boat took 30 to 35 hrs.
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