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/

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?

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