Common knowledge is that we should top up our fuel tank for the winter
sleep. Argument is that otherwise the temp changes will continuously
condense water into the tank, as moist air is pulled in, condensed,
and then expelled.

I have no doubt that the effect is real, but wonder how big it
actually is. How much water per gallon (or liter) of air would
condense in one cycle of some plausible temperature range and some
plausible outside dew point?

(I think I know how to calculate this, but wonder if its already been done?)

Common knowledge is entirely faulty.

Fuel oil when manufactured (cracked, etc.) is rendered essentially
'dry'. Water (vapor in the air) 'equilibrates' eventually until the
oil is saturated with water from the atmosphere ..... and only after
the oil is SATURATED with water does the 'condensation' become
apparent. Simple speak: if your fuel is condensing water it means
that its laid around with an open vent too long and its now LOADED
with water.

The BEST is to totally empty the tank for the winter, take home the
fuel and burn it in your heater.
EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

"RichH" wrote in message ...
Common knowledge is entirely faulty.

Fuel oil when manufactured (cracked, etc.) is rendered essentially
'dry'. Water (vapor in the air) 'equilibrates' eventually until the
oil is saturated with water from the atmosphere ..... and only after
the oil is SATURATED with water does the 'condensation' become
apparent. Simple speak: if your fuel is condensing water it means
that its laid around with an open vent too long and its now LOADED
with water.

The BEST is to totally empty the tank for the winter, take home the
fuel and burn it in your heater.
EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

No doubt that emptying the tank and the fuel system may be a good thing to do.

Since 1982 I have always stored the boat for winter (Canadian Maritime) with a full tank. At time I did add some diesel conditioner.

I never had any fuel problem. The water separator must have worked well. Now with the new boat the water separator is more Hi-Tech and I do not know if I should add some fuel stabilizer.

Last year I did not add any and I had no fuel problem. This year I am thinking about adding some stabilizer.

BTW. Over here during the winter the sun may shine on the boat and the temperature may get up and when the night drives in it gets way below freezing. I wonder what takes place in the empty full tank and conduits?

On Wed, 12 Nov 2008 16:45:06 -0800 (PST), RichH
wrote:

Common knowledge is entirely faulty.

Fuel oil when manufactured (cracked, etc.) is rendered essentially
'dry'. Water (vapor in the air) 'equilibrates' eventually until the
oil is saturated with water from the atmosphere ..... and only after
the oil is SATURATED with water does the 'condensation' become
apparent. Simple speak: if your fuel is condensing water it means
that its laid around with an open vent too long and its now LOADED
with water.

The BEST is to totally empty the tank for the winter, take home the
fuel and burn it in your heater.
EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

Oh, but they DO. Any variation in temperature of the air surrounding
the tank will cause a pumping action. Temp goes up, the air in the
tank expands and finds a way out to create equilibrium. Temp goes
down, the tank inhales air containing moisture.

Unless of course you think your tank is completely pressure sealed, of
course.

On Thu, 13 Nov 2008 06:34:37 -0500, wrote:

On Wed, 12 Nov 2008 16:45:06 -0800 (PST), RichH
wrote:

Common knowledge is entirely faulty.

Fuel oil when manufactured (cracked, etc.) is rendered essentially
'dry'. Water (vapor in the air) 'equilibrates' eventually until the
oil is saturated with water from the atmosphere ..... and only after
the oil is SATURATED with water does the 'condensation' become
apparent. Simple speak: if your fuel is condensing water it means
that its laid around with an open vent too long and its now LOADED
with water.

The BEST is to totally empty the tank for the winter, take home the
fuel and burn it in your heater.
EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

Oh, but they DO. Any variation in temperature of the air surrounding
the tank will cause a pumping action. Temp goes up, the air in the
tank expands and finds a way out to create equilibrium. Temp goes
down, the tank inhales air containing moisture.

Unless of course you think your tank is completely pressure sealed, of
course.


The variable is, of course, the volume of airspace in the tank. If, as
I do, you fill the tank full - right up to the filler outlet there is
very, very little pumping action. further, if the tank is filled into
the filler hose and the cap screwed down that access is now closed to
the atmosphere and the only access is through the breather hoses - say
1/2" hose about 3 ft. long, or about 7 cu inches. How much volume
change is going to occur in that space and even assuming a extremely
high humidity how much water accumulates?
Cheers,

Bruce in Bangkok
(bpaige125atgmaildotcom)

wrote:


Oh, but they DO. Any variation in temperature of the air surrounding
the tank will cause a pumping action. Temp goes up, the air in the
tank expands and finds a way out to create equilibrium. Temp goes
down, the tank inhales air containing moisture.

So? The moisture just goes right out again with the air. In the case of
the empty tank for the winter Rich was discussing, there is no thermal mass
of fuel to create the temperature differentials that would create
significant condensation. Even in the case of tanks partially full of fuel
condensation on a tank top is unlikely to be a significant issue (see my
reply to Larrry).

--
Roger Long

http://www.yachtsurvey.com/myth_of_c...fuel_tanks.htm

On 2008-11-13 10:56:30 -0500, Gordon said:

http://www.yachtsurvey.com/myth_of_c...fuel_tanks.htm

How did you find that? I went there first of course, but couldn't find it.

"Wasted" a bit of time, as usual, as I found a half-dozen articles of interest.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Thu, 13 Nov 2008 12:07:51 -0500, wrote:

No, unfortunately, the moisture is heavier than air and settles in the
tank, where it remains.

Unfortunately, no. Water vapor has a molecular weight of 18, air is
29. Density varies directly with molecular weight.

Casady

On Thu, 13 Nov 2008 14:50:12 -0500, wrote:

On Thu, 13 Nov 2008 19:43:37 GMT, (Richard
Casady) wrote:

On Thu, 13 Nov 2008 12:07:51 -0500, wrote:

No, unfortunately, the moisture is heavier than air and settles in the
tank, where it remains.

Unfortunately, no. Water vapor has a molecular weight of 18, air is
29. Density varies directly with molecular weight.

Casady

So, if you fill a balloon with water, it will fly? Amazing! Does NASA
know about this?

What part of vapor didn't you understand?

Casady