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?