wrote

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

Not necessarily. The surroundings have to cool differerentially or to the
extent that there is water on every surface. Even then, the water doesn't
necessarily fall off the surface and into the fuel. I was in my boat nearly
every day working on it last winter and I never saw conditions that made me
think that the tank top would have been covered with water drops. I also
kept my tanks drawn down most of the winter because I was installing my new
fuel system. My boat was in a shed that warmed up a lot with a very damp
floor so there was lots of temperature differential.

When in turmoil, when in doubt, always try a little perspective:

The "pumping action" of temperature changes is orders of magnitude less than
the pumping due to fuel sloshing around with boat motion.
The temperature differentials in summer with cool water and hot sun are much
greater than for a boat hauled out in the winter.
The cold air of winter is generally drier. Condensation happens because air
cools and can't hold as much moisture. Much of that process has already
happend by the time winter air gets into your tank.

If filling your tanks is really vital in winter, big time problems in summer
is what we would be discussing here.

It still a good, but not vital, idea to minimize fuel surface area contact
with air over long periods of storage. One way to do this is to fill the
tanks into the vents. Another is to empty the tanks. I can't do the latter
so I do the former. Not doing anything is unlikely to lead to problems so
severe they can't be dealt with with something like Startron.

My boat was laid up for six years near Detroit by the former owner with a
partially filled fuel tank and I had to deal with it after I bought it. The
fuel turned to partly to jelly that wouldn't go through the filters and
there was a mega clean up but there was no water in the bottom of the tank.
There was no real alge growth either. The fuel just evaporated off ligher
elements, oxidized, and aged.

--
Roger Long

On Thu, 13 Nov 2008 09:02:01 -0500, "Roger Long"
wrote:


When in turmoil, when in doubt, always try a little perspective:

Reminds me of the Honda owners who insist on changing brake fluid
every couple years because brake fluid is hygroscopic.
They love that word.
Doesn't matter that the braking system is closed to the atmosphere.
Change that brake fluid. And use Honda fluid to be "safe."
When I mentioned the 13-year old brake fluid in my Celebrity was
performing just fine I was accused of being a road menace.
That's why I love usenet.

--Vic

On Thu, 13 Nov 2008 09:02:01 -0500, "Roger Long"
wrote:

My boat was laid up for six years near Detroit by the former owner with a
partially filled fuel tank and I had to deal with it after I bought it. The
fuel turned to partly to jelly that wouldn't go through the filters and
there was a mega clean up but there was no water in the bottom of the tank.
There was no real alge growth either. The fuel just evaporated off ligher
elements, oxidized, and aged.

Algae is a green plant, does photosynthesis and all that, and cannot
survive without light. Fungus can grow in fuel tanks, the stuff feeds
on the fuel, but it has to have water. They have antifungus, anti
water additives for jet fuel. The first Learjets lacked fuel heaters,
and you added Prist, from an pressurized can, through a hose clipped
to the fuel nozzle. That way it mixed.

If you evaporate all the light fractions, could this decrease the
solubility of the wax? Maybe wax had something to do with the jelly.
Cold fuel waxes out, and it plugs filters. [One solution is to mix
50/50 with #1 fuel. At least one station in Des Moines sells the
blend, during the Winter.]

Casady

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 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)

The threat of water in the fuel is real, but it shouldn't be a problem. You
must have a business process in place to manage the problem. The most likely
cause is being delivered fuel with already absorbed water. The second threat
is fuel is hygroscopic and absorbs moisture from the atmosphere. This is a
low threat in cold temperatures because the air will not contain much water.
However, this is a big problem in warm humid climes. The consequences are
tank corrosion, bacterial growth and fuel system failure. The decision to
fill your tanks are really fuel cost and saving opportunities based. Your
protection against the threat are corrosion proof tanks, biocide additives
and a centrifuge water/fuel separator (fuel polishing system). The risk
cannot be avoided, only mitigated.
Steve

"Marc Auslander" wrote in message
...
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?)

On 12 Nov 2008 18:03:00 -0500, Marc Auslander
wrote:

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?)

Google groups is getting worse for finding stuff..

"
On Fri, 28 Mar 2008 18:08:53 -0400, "Roger Long"
wrote:

OK, worst case, 100% humidity at 80 F., and it all condenses out into the
tank. What volume of water are we talking about for each cubic foot of air?

1 cubic foot = 0.028 316 846 592 000 066 cubic meter
http://www.onlineconversion.com/volume.htm
80 degree Fahrenheit = 26.6666667 degree Celsius
http://www.onlineconversion.com/temperature.htm
At sea level and at 20 °C, dry air has a density of approximately 1.2
kg/m3
http://en.wikipedia.org/wiki/Density_of_air
approx 20g h2o / kg air
http://en.wikipedia.org/wiki/Humidity

0.028 x 1.2 x 20 = 0.672 grams/ccs/ml of water.

"

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

On Thu, 13 Nov 2008 21:23:26 -0800 (PST), "
wrote:

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

The fact that they can't convert from degrees C to F properly spoils
it a bit..