My cx 25

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joe2700
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Re: My cx 25

Post by joe2700 »

joe2700 wrote: Thu Sep 13, 2018 1:34 pm
Jaysen wrote: Thu Sep 13, 2018 1:27 pm
Does that mean that actual tank capacity is variable? EX if you have a half full tank, the tank may expand inward making the "empty" portion less than the actual volume of 1/2 the tank capacity.

Or would that only happen if the tank was restricted from expansion?

Thanks.
I'm under the impression it's kind of a one time thing, and that once it's grown over that first month it will basically stay expanded, unless maybe you let it completely air out for a long time. I think if you restrict it from expanding outwards like its supposed to it may deform. All this is conjecture on my part though. Just what I've gathered from the manufacturers instructions and Boatowners Mechanical and Electrical Manual which I kind of consider the bible of marine systems.

I think you actually get a bit more capacity after this process is done, as it's expanding lengthwise not just getting thicker, not positive though.

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Jaysen
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Re: My cx 25

Post by Jaysen »

Hmmm... seems like a simple chem bath at manufacture would address that.

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fallguy1000
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Re: My cx 25

Post by fallguy1000 »

The expansion and contraction is thermal. Boat in Bahamas and it is 100F the fuel expands and the tank expands.

The expansion of a 1 meter polyethylene tank from 23C to 40c is about 0.3cm

It isn't a one n done.

If the temperature drops to say 6C, the tank will go from the expanded size at 40C down to normal size at 23C and then shrink to 0.3cm below a meter at 6C.

Danilo - leave a good size gap between the tanks; like a full inch or at least about 3/4" minimum.

And no foam.

Foam is also not advisable in ally tanks. The tanks needs space for thermal expansion.
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joe2700
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Re: My cx 25

Post by joe2700 »

fallguy1000 wrote: Thu Sep 13, 2018 5:51 pm The expansion and contraction is thermal.
That may also be true, but polyethylene definitely expands when exposed to gasoline.

From Moeller as an example:
Allow 3% expansion of the fuel tank in all directions. Hydrocarbon swell occurs when gasoline or diesel fuel soaks into the fuel tank material. (Example: Initial size 40"L x 24"W x 18"H = Expanded size 41.2"L x 24.7"W x 18.5"H) Design the fuel tank compartment to allow growth equally. Hold down brackets / braces must be installed to prevent damage to the fuel tank even after hydrocarbon expansions occur.
http://moellermarine.com/wp-content/upl ... marine.pdf

fallguy1000
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Re: My cx 25

Post by fallguy1000 »

joe2700 wrote: Thu Sep 13, 2018 6:28 pm
fallguy1000 wrote: Thu Sep 13, 2018 5:51 pm The expansion and contraction is thermal.
That may also be true, but polyethylene definitely expands when exposed to gasoline.

From Moeller as an example:
Allow 3% expansion of the fuel tank in all directions. Hydrocarbon swell occurs when gasoline or diesel fuel soaks into the fuel tank material. (Example: Initial size 40"L x 24"W x 18"H = Expanded size 41.2"L x 24.7"W x 18.5"H) Design the fuel tank compartment to allow growth equally. Hold down brackets / braces must be installed to prevent damage to the fuel tank even after hydrocarbon expansions occur.
http://moellermarine.com/wp-content/upl ... marine.pdf
Thanks. I learned something today. I couldn't understand how the amounts were so much lower than the allowances I am using on my own build to meet 2.5%. I have a 47" tank and have a 48" space, so I am just a tad over the 2% amount. The tank is surrounded by bulkheads and they aren't moving. The good news is I have an extra inch on the width as well, so that will give me a little extra, but in the wrong direction.

Anyhow, hopefully with all this advice, Danilo will build properly.
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dalnilo
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Re: My cx 25

Post by dalnilo »

ok no foam on the sides of the tank, under the tank I can put according to you?

joe2700
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Re: My cx 25

Post by joe2700 »

dalnilo wrote: Fri Sep 14, 2018 12:32 pm ok no foam on the sides of the tank, under the tank I can put according to you?
I would defer to the instructions of whoever manufactured your tank. Generally tanks like this are mounted on a hard surface with neoprene strips between the tank and the support.That would be a lot of weight to put foam under and I wouldn't want foam up against a fuel tank myself anyway. But whoever built the tank should have instructions. Personally I wouldn't foam that compartment at all.

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Re: My cx 25

Post by Fuzz »

I think the rubber strips are something needed for aluminium tanks. I do not think they are needed for plastic tanks. But as advised check with the manufacturer and do as they say.

danieloldhouse
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Re: My cx 25

Post by danieloldhouse »

Are those tanks HT-Tanks from Nautica FAM?

dalnilo
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Re: My cx 25

Post by dalnilo »

danieloldhouse wrote: Fri Sep 14, 2018 6:01 pm Are those tanks HT-Tanks from Nautica FAM?
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