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 2008-11-12 18:03:00 -0500, Marc Auslander
said:

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?)

I've seen an expert analysis by a surveyor fairly recently, but can't
find it now.

Essentially, he proved (at least to me) that the water isn't from
condensation but primarily from leaky fuel caps, both on the boat and
on the marina's tanks.

The volume of water than can be condensed out of the volume of air
contained in a fuel tank isn't significant, especially since air flow
in a typical tank is trivial.

--
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/

Marc Auslander wrote in
:

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?)


You can't calculate it because you can't calculate the humidity of the air
from hour to hour, an immense variable.

It doesn't matter how much....it happens. EVERY airplane at the airport
hangar has tanks filled to the lip because of it. Water in their fuel
spells disaster.

Larry wrote:


It doesn't matter how much....it happens. EVERY airplane at the
airport hangar has tanks filled to the lip because of it. Water in
their fuel spells disaster.

Once again, this simply isn't true and in cases where it is it is because
common knowledge is faulty as Rich says. As a pilot and manager of an
aircraft for a flying club, I checked fuel in an aircraft through the bottom
drain nearly daily year round for a decade and never found a drop except
once after driving rain when the fill cap was not tightened. Like many
aircraft, this one was kept with slack tanks because only two people could
fly it with full tanks and baggage and we didn't want someone to arrive at
the airport and be unable to take off without spending hundreds of dollars
to dispose of drained fuel. This was an aircraft tied down about 200 yards
from the ocean.

There are some "wet wing" aircraft constructions where condensation is more
of a problem but the wings of my plane were similar to a boat in that they
were aluminum inside the wing structure with an air space.

Filling the tanks for the long winter storage, which I have been doing,
helps because it dramatically reduces the surface area of fuel exposed to
air. This works only if you fill up into the vents slightly. I would drain
except I can't get the last inch of fuel out of my tanks. This year, I'm
going to take Rich's suggestion and pipe my sounding tube to a container of
Silica Gel after taping over the vent. In this climate, I haven't had
enough trouble with water problems to make this a permanent installation but
it's a neat idea for southern boats.

--
Roger Long

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 02:09:13 GMT, Jere Lull wrote:

On 2008-11-12 18:03:00 -0500, Marc Auslander
said:

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?)

I've seen an expert analysis by a surveyor fairly recently, but can't
find it now.

Essentially, he proved (at least to me) that the water isn't from
condensation but primarily from leaky fuel caps, both on the boat and
on the marina's tanks.

The volume of water than can be condensed out of the volume of air
contained in a fuel tank isn't significant, especially since air flow
in a typical tank is trivial.

But the small amount of water that enters each time the surroundings
cool, stays there and accumulates. Over a 4 or 6 month layup?

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)

On Thu, 13 Nov 2008 05:54:34 -0500, "Roger Long"
wrote:

Larry wrote:


It doesn't matter how much....it happens. EVERY airplane at the
airport hangar has tanks filled to the lip because of it. Water in
their fuel spells disaster.

Once again, this simply isn't true and in cases where it is it is because
common knowledge is faulty as Rich says. As a pilot and manager of an
aircraft for a flying club, I checked fuel in an aircraft through the bottom
drain nearly daily year round for a decade and never found a drop except
once after driving rain when the fill cap was not tightened. Like many
aircraft, this one was kept with slack tanks because only two people could
fly it with full tanks and baggage and we didn't want someone to arrive at
the airport and be unable to take off without spending hundreds of dollars
to dispose of drained fuel. This was an aircraft tied down about 200 yards
from the ocean.

There are some "wet wing" aircraft constructions where condensation is more
of a problem but the wings of my plane were similar to a boat in that they
were aluminum inside the wing structure with an air space.

Filling the tanks for the long winter storage, which I have been doing,
helps because it dramatically reduces the surface area of fuel exposed to
air. This works only if you fill up into the vents slightly. I would drain
except I can't get the last inch of fuel out of my tanks. This year, I'm
going to take Rich's suggestion and pipe my sounding tube to a container of
Silica Gel after taping over the vent. In this climate, I haven't had
enough trouble with water problems to make this a permanent installation but
it's a neat idea for southern boats.

For 20 years I was involved in aircraft maintenance, both big and
little airplanes. The common practice was to leave the tanks the way
they were when the plane landed as fuel loads were dependent on cargo
to be carried and length of flight. In fact this was most noticeable
with big aircraft - B-52's for example might take a full fuel load or
if they had an extremely heavy bomb load might take off with minimum
fuel and re-fuel immediately on reaching cruising altitude.

Cheers,

Bruce in Bangkok
(bpaige125atgmaildotcom)