Sweating Hull

[CARL]

Hi, need some advice hear. Having dried the boat about a week ago for general maintenance ,i expected to have to tend to some blisters and was not dissapointed as 4or5 have reared their heads up so in due corse will grind back , seal, and fair with epoxy not a big problem. This time however i noticed today while most of the hull had dried, on both sides of hull at the stern ,an area of about 3ft by 2ft appeares to be sweating ,or another way to describe would be to say it looks just like condensation would on a large bit of glass. The start , finnish line if you like, is very pronounced, staight lines.One thing i can say is that the fuel and water tanks,each approx 100 gal and in stainless are here.Any one come accross this ? thanks in advance.

[boatman61]

Is this area mainly in the shadow most of the time... if so its quite likly that the antifoul is absobing surface dew whatever and due to the proximity of the tanks and the cooler interior is not drying as fast.. its warmed enough to be drawn but then the suns moved so it has not vapourised into the atmosphere...
Just guessing right now...

[Sailmonkey]

Are the tanks cold and in direct contact with the hull? if it's cold at night and warmish/humid at day i think the answer has already presented itself. If more proof is needed, have a cold beer on a warm day

[David M]

There is a temperature difference because the temperature of the liquid on the other side of the bulkhead is different from the air temperature inside the boat. The temperature of the liquid is below the dew point of the rooms air.

When the temperature of a surface drops below the dew point, condensation will occur. The solution is to add insulation, which will reduce the heat transference, so the surface temperature remains above the dew point of the air in the room. Or get a dehumidifier to lower the rooms dew point.

[CARL]

thanks to all for replying, i think all points are valid, we have had quite a cold snap lately,today was much milder,no heating in boat wouldnt surprise me if water in tanks would be practicly frozen so the dew ,condesation theory sounds probable,just me thinking the worst,thanks again i will sleep better now.