Keep the window cracked open?

[Hello Below]

Temperature difference is the issue. As long as the interior boat temp is the same as the outside temp there is no condensation. When the interior temp increases due to either a heater or a solar hit there is a problem when the temp drops as the cooler air will not hold as much moisture. It has to go somewhere and condenses on cooler surfaces.

No argument here, with respect to condensations. However, humidity runs high in the PNW from Nov to Apr. Right now the outside humidity is 90% and this is typical for this time of year. If there is ventilation and/or no water extracted from the inside air then the inside humidity would also be 90%. Would this not cause a potential problem with mold, mildew and the like?

 

[Chris Patterson]

No argument here, with respect to condensations. However, humidity runs high in the PNW from Nov to Apr. Right now the outside humidity is 90% and this is typical for this time of year. If there is ventilation and/or no water extracted from the inside air then the inside humidity would also be 90%. Would this not cause a potential problem with mold, mildew and the like?

That's exactly what I was saying before, and it seems an identical thread has been started on this, but damn. It doesn't take a rocket scientist to figure out that 90 percent humidity is 'ventilated' into a boat equals 90 percent. I mean think about it. I quit....

 

[wamwam1]

90 % humidity air introduced to a boat will absorb some water if there is, for example, bilge water, assuming all is at ambient temperature. That now higher humidity air must be removed from the boat and replaced by ambient air. Failure to ventilate will cause a slow build up in humidity in the air in the boat, assuming bilge water, for example, is present and when that air is cooled on the hull condensation will occur. A heater in the boat makes this mechanism worse. The best thing to do is have as much ventilation as possible and avoid a heater, unless it is a really big heater.

 

[Mikem]

I have three of those round WM heater dh units going all the time plus an oil filled heater to keep the temp above 50. That oil filled heater also prevents my fresh water lines from freezing during some of our rare cold snaps. My dorado vents are also open and I crack the overhead hatches in the heads. 11 years in the PNW and no mold or mildew.