ventilation

any of you following our blog know we found a mold disaster when we returned to our CC36. Ventilation seems to be the only preventative. I am curious about the pro and con of 24hr ventilation versus day time only. Reggie Sent from Outlook<http://aka.ms/weboutlook>

I think getting as much ventilation as you can and run one of those 90 watt things with a fan in them. They are not heaters, just designed to create air flow due to currents they set up. You can see what I tried on L-36.com. Search for "humidity". I just looked on Google and could not find a reference to doing what I would call active ventilation but that is the wrong term anyway. The basic idea is that you want your boat to be dry so you want to vent when the air outside has less moisture in it than the air inside. Note I said moisture and not humidity. It is possible to build a system that measures the differential vapor pressure and open vents when appropriate. I have never heard of anyone doing that on a boat and I am not sure of the details. I will just say this. Hot air holds more moisture than cold air so it very well may be that what you want to do it open the vents at night and close them during the day. I am not saying that is the case, but it might be so unless you know, I would not do daytime only venting. I know closing the boat up and heating it is counter productive as you will just get more moisture in the boat and it will be hot. Ideal conditions for growing stuff. Basically I think there is some law that says that a closed container that is not hermetic will end up being at 100% humidity eventually. Allen On Tue, Jan 30, 2018 at 3:51 AM, r good my… [at] hotmail.com [Cal_Boats] < Ca… [at] yahoogroups.com> wrote: > > > any of you following our blog know we found a mold disaster when we > returned to our CC36. Ventilation seems to be the only preventative. I am > curious about the pro and con of 24hr ventilation versus day time only. > > Reggie > > > Sent from Outlook <http://aka.ms/weboutlook> > > >

Mold tends to grow when the Relative humidity is over 60%. Depending on the area, ventilation may or may not help much. If the boat is in water that is cold and the outside air is warm, if enough air is not brought in to raise the temp of the boat and or the outside air has a high relative humidity, bringing outside air in can actually increase the relative humidity. A dehumidifier and pumping the water out is the only way to pull the water out of the air and dry the boat out. > On Jan 30, 2018, at 6:51 AM, r good my… [at] hotmail.com [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > any of you following our blog know we found a mold disaster when we returned to our CC36. Ventilation seems to be the only preventative. I am curious about the pro and con of 24hr ventilation versus day time only. > Reggie > > Sent from Outlook >

In our experience in the 15+ yrs we have owned our Cal in NC, solar vents work best. We installed solar vents 1st. Replaced them with 24hr vent when they wore out. Replace the 24hr vents with solar when they quit working. The 24 hr vents allowed the mold to grow faster. The solar only brought in dryer air. Weather here in NC is “clear and cold, or warm and rain”. We also have passive vents in the main cabin. One pointed forward and one abaft. We will plug in the winter when aboard. If we do not uncover, it will help the mold start. John Raxter 336-210-8073 (m) On Jan 31, 2018, at 12:00 AM, Allen Edwards al… [at] gmail.com [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: I think getting as much ventilation as you can and run one of those 90 watt things with a fan in them. They are not heaters, just designed to create air flow due to currents they set up. You can see what I tried on L-36.com. Search for "humidity". I just looked on Google and could not find a reference to doing what I would call active ventilation but that is the wrong term anyway. The basic idea is that you want your boat to be dry so you want to vent when the air outside has less moisture in it than the air inside. Note I said moisture and not humidity. It is possible to build a system that measures the differential vapor pressure and open vents when appropriate. I have never heard of anyone doing that on a boat and I am not sure of the details. I will just say this. Hot air holds more moisture than cold air so it very well may be that what you want to do it open the vents at night and close them during the day. I am not saying that is the case, but it might be so unless you know, I would not do daytime only venting. I know closing the boat up and heating it is counter productive as you will just get more moisture in the boat and it will be hot. Ideal conditions for growing stuff. Basically I think there is some law that says that a closed container that is not hermetic will end up being at 100% humidity eventually. Allen > On Tue, Jan 30, 2018 at 3:51 AM, r good my… [at] hotmail.com [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > any of you following our blog know we found a mold disaster when we returned to our CC36. Ventilation seems to be the only preventative. I am curious about the pro and con of 24hr ventilation versus day time only. > Reggie > > Sent from Outlook

I still cannot find the article that talks about venting based on vapor pressure differences. I can say that opening up Papoose to outside air and running the 90 watt heater with the fan made a huge difference. The most noticeable thing was in the lazarettes. Before I started propping them open a little, they would be dripping wet whenever I did open them. Now they stay dry. I just keep them open about an inch. They don't have hinges so I prop open the back edge and any rain water will drain into the cockpit. I also removed some bulkhead covers so that now the entire boat is open and air can flow throughout. I have solar vents without batteries so I guess these are not 24 hour vents. But I did a calculation based on a NOAA site that calculates how much water is in the air. In the last few days the high temperature was 68F and 75% humidity. The low was 52F and 90% humidity. Probably not what some of you are seeing but we suffer through it... Anyway, the warm air has 13 g/m3 of water and the cold air has 9 g/m3 so the cold air at 90% humidity has less moisture than the warm air. Theoretically if I could draw in cold dry air and seal the boat during the day I think it would be dryer. The water is about 55F. I am guessing that my experience is probably not that transferable to areas that freeze with very cold water and humid days. Clearly a dehumidifier and a sealed boat will keep the boat dry but short of that, the best you can do is to have the water content inside the same as outside. Allen On Wed, Jan 31, 2018 at 5:30 AM, John Raxter <jr… [at] att.net> wrote: > In our experience in the 15+ yrs we have owned our Cal in NC, solar vents > work best. We installed solar vents 1st. Replaced them with 24hr vent when > they wore out. Replace the 24hr vents with solar when they quit working. > > The 24 hr vents allowed the mold to grow faster. The solar only brought in > dryer air. Weather here in NC is “clear and cold, or warm and rain”. > > We also have passive vents in the main cabin. One pointed forward and one > abaft. We will plug in the winter when aboard. If we do not uncover, it > will help the mold start. > > John Raxter > 336-210-8073 <(336)%20210-8073> (m) > > On Jan 31, 2018, at 12:00 AM, Allen Edwards al… [at] gmail.com > [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > > I think getting as much ventilation as you can and run one of those 90 > watt things with a fan in them. They are not heaters, just designed to > create air flow due to currents they set up. You can see what I tried on > L-36.com. Search for "humidity". > > I just looked on Google and could not find a reference to doing what I > would call active ventilation but that is the wrong term anyway. The basic > idea is that you want your boat to be dry so you want to vent when the air > outside has less moisture in it than the air inside. Note I said moisture > and not humidity. It is possible to build a system that measures the > differential vapor pressure and open vents when appropriate. I have never > heard of anyone doing that on a boat and I am not sure of the details. I > will just say this. Hot air holds more moisture than cold air so it very > well may be that what you want to do it open the vents at night and close > them during the day. I am not saying that is the case, but it might be so > unless you know, I would not do daytime only venting. > > I know closing the boat up and heating it is counter productive as you > will just get more moisture in the boat and it will be hot. Ideal > conditions for growing stuff. Basically I think there is some law that > says that a closed container that is not hermetic will end up being at 100% > humidity eventually. > > Allen > > On Tue, Jan 30, 2018 at 3:51 AM, r good my… [at] hotmail.com [Cal_Boats] < > Ca… [at] yahoogroups.com> wrote: > >> >> >> any of you following our blog know we found a mold disaster when we >> returned to our CC36. Ventilation seems to be the only preventative. I am >> curious about the pro and con of 24hr ventilation versus day time only. >> >> Reggie >> >> >> Sent from Outlook <http://aka.ms/weboutlook> >> >> > >

On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: > > > In our experience in the 15+ yrs we have owned our Cal in NC, solar > vents work best. We installed solar vents 1st. Replaced them with 24hr > vent when they wore out. Replace the 24hr vents with solar when they > quit working. > > The 24 hr vents allowed the mold to grow faster. The solar only > brought in dryer air. Weather here in NC is “clear and cold, or warm > and rain”. One issue is the temp of surfaces. Moisture tends to condense out on cold surfaces. Lightweight camping tents use a "rain fly" that has 2 functions. One is to be waterproof, with the tent itself underneath having a permeable surface so human moisture (breathing, sweating) can disperse. The other is to serve as a radiant heat shield. Surfaces radiate heat toward cold dark areas--it's why we get dew on the truck at night, or in this season we in Michigan have really low nighttime temps when the sky is clear. The truck and the earth radiate heat toward the cold dark sky. Clouds, or the rain fly, interrupt that and keep things warmer. So bringing in air at night may be counterproductive if the hull, decks, and overhead are cold. They may just serve as condensing surfaces. My other boat has a big boom tent cover to protect the mahogany and spruce. But it also has the same effect as the camping tent's rain fly--it serves as a radiant heat barrier. I get a lot more mildew on the overhead where the cover isn't than where it is. That boat is passively and incompletely ventilated. Chris Campbell > >

It really is as simple as put a hygrometer in the boat and do what ever you have to do to reduce humidity. Put one under the seat lockers to see if there is a difference between general cabin humidity and humidity in the small spaces next to the hull. Cold hull + confined space + warm moist air = high relative humidity > On Jan 31, 2018, at 11:02 AM, ccampbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > >> On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: >> In our experience in the 15+ yrs we have owned our Cal in NC, solar vents work best. We installed solar vents 1st. Replaced them with 24hr vent when they wore out. Replace the 24hr vents with solar when they quit working. >> >> The 24 hr vents allowed the mold to grow faster. The solar only brought in dryer air. Weather here in NC is “clear and cold, or warm and rain”. > > One issue is the temp of surfaces. Moisture tends to condense out on cold surfaces. Lightweight camping tents use a "rain fly" that has 2 functions. One is to be waterproof, with the tent itself underneath having a permeable surface so human moisture (breathing, sweating) can disperse. The other is to serve as a radiant heat shield. Surfaces radiate heat toward cold dark areas--it's why we get dew on the truck at night, or in this season we in Michigan have really low nighttime temps when the sky is clear. The truck and the earth radiate heat toward the cold dark sky. Clouds, or the rain fly, interrupt that and keep things warmer. So bringing in air at night may be counterproductive if the hull, decks, and overhead are cold. They may just serve as condensing surfaces. > > My other boat has a big boom tent cover to protect the mahogany and spruce. But it also has the same effect as the camping tent's rain fly--it serves as a radiant heat barrier. I get a lot more mildew on the overhead where the cover isn't than where it is. That boat is passively and incompletely ventilated. > > Chris Campbell >> >> > >

With all due respect, I think you are more likely to get condensation with warm air than with cold. In my example with 68F air at 75% the dew point is 60F so that air hitting the 55 degree hull would condens out where the 52 degree air at 90% would not because the dew point is 43 F. That is why given the choice I would rather vent with the cold relatively dry air even though it has a higher RH. But as I am not going to install dampers and vapor pressure monitors, I just vent. If I were in Florida, I would get a dehumidifier. Allen On Wed, Jan 31, 2018 at 8:02 AM, ccampbell cc… [at] lsnm.org [Cal_Boats] < Ca… [at] yahoogroups.com> wrote: > > > > > On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: > > In our experience in the 15+ yrs we have owned our Cal in NC, solar vents > work best. We installed solar vents 1st. Replaced them with 24hr vent when > they wore out. Replace the 24hr vents with solar when they quit working. > > The 24 hr vents allowed the mold to grow faster. The solar only brought in > dryer air. Weather here in NC is “clear and cold, or warm and rain”. > > > One issue is the temp of surfaces. Moisture tends to condense out on cold > surfaces. Lightweight camping tents use a "rain fly" that has 2 > functions. One is to be waterproof, with the tent itself underneath having > a permeable surface so human moisture (breathing, sweating) can disperse. > The other is to serve as a radiant heat shield. Surfaces radiate heat > toward cold dark areas--it's why we get dew on the truck at night, or in > this season we in Michigan have really low nighttime temps when the sky is > clear. The truck and the earth radiate heat toward the cold dark sky. > Clouds, or the rain fly, interrupt that and keep things warmer. So > bringing in air at night may be counterproductive if the hull, decks, and > overhead are cold. They may just serve as condensing surfaces. > > My other boat has a big boom tent cover to protect the mahogany and > spruce. But it also has the same effect as the camping tent's rain fly--it > serves as a radiant heat barrier. I get a lot more mildew on the overhead > where the cover isn't than where it is. That boat is passively and > incompletely ventilated. > > Chris Campbell > > > > > >

A hygrometer is about $10 and would let you know how successful your venting was. > On Jan 31, 2018, at 11:50 AM, Allen Edwards al… [at] gmail.com [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > With all due respect, I think you are more likely to get condensation with warm air than with cold. In my example with 68F air at 75% the dew point is 60F so that air hitting the 55 degree hull would condens out where the 52 degree air at 90% would not because the dew point is 43 F. That is why given the choice I would rather vent with the cold relatively dry air even though it has a higher RH. But as I am not going to install dampers and vapor pressure monitors, I just vent. If I were in Florida, I would get a dehumidifier. > > Allen > >> On Wed, Jan 31, 2018 at 8:02 AM, ccampbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: >> >> >> >>> On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: >>> In our experience in the 15+ yrs we have owned our Cal in NC, solar vents work best. We installed solar vents 1st. Replaced them with 24hr vent when they wore out. Replace the 24hr vents with solar when they quit working. >>> >>> The 24 hr vents allowed the mold to grow faster. The solar only brought in dryer air. Weather here in NC is “clear and cold, or warm and rain”. >> >> One issue is the temp of surfaces. Moisture tends to condense out on cold surfaces. Lightweight camping tents use a "rain fly" that has 2 functions. One is to be waterproof, with the tent itself underneath having a permeable surface so human moisture (breathing, sweating) can disperse. The other is to serve as a radiant heat shield. Surfaces radiate heat toward cold dark areas--it's why we get dew on the truck at night, or in this season we in Michigan have really low nighttime temps when the sky is clear. The truck and the earth radiate heat toward the cold dark sky. Clouds, or the rain fly, interrupt that and keep things warmer. So bringing in air at night may be counterproductive if the hull, decks, and overhead are cold. They may just serve as condensing surfaces. >> >> My other boat has a big boom tent cover to protect the mahogany and spruce. But it also has the same effect as the camping tent's rain fly--it serves as a radiant heat barrier. I get a lot more mildew on the overhead where the cover isn't than where it is. That boat is passively and incompletely ventilated. >> >> Chris Campbell >>> >>> >> > >

If you have not already done so, I suggest installing an underlayment of elevated hard plastic or rubber grid squares beneath your bunk mattresses. We have done this, as well as gone one square up the sides so the bedding doesn't touch the hull and air can flow under and around. It helps a lot, and bedding stays drier from not soaking side condensation. I bought a number of 40 square foot boxes of this decking type stuff. But I am in California. I also washed down a bit of mildew on our trawler last year, then put a mildew preventer on after, it seems to be working. Going to use on cal 36 this year. But it's nasty smelling for a day or two, don't inhale. I'm not sure about safety after it dries, as obviously it's toxic to mold. Helen Sent from Yahoo Mail on Android On Wed, Jan 31, 2018 at 11:05 AM, Allen Edwards al… [at] gmail.com [Cal_Boats]<Ca… [at] yahoogroups.com> wrote: With all due respect, I think you are more likely to get condensation with warm air than with cold. In my example with 68F air at 75% the dew point is 60F so that air hitting the 55 degree hull would condens out where the 52 degree air at 90% would not because the dew point is 43 F. That is why given the choice I would rather vent with the cold relatively dry air even though it has a higher RH. But as I am not going to install dampers and vapor pressure monitors, I just vent. If I were in Florida, I would get a dehumidifier. Allen On Wed, Jan 31, 2018 at 8:02 AM, ccampbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: In our experience in the 15+ yrs we have owned our Cal in NC, solar vents work best. We installed solar vents 1st. Replaced them with 24hr vent when they wore out. Replace the 24hr vents with solar when they quit working. The 24 hr vents allowed the mold to grow faster. The solar only brought in dryer air. Weather here in NC is “clear and cold, or warm and rain”. One issue is the temp of surfaces. Moisture tends to condense out on cold surfaces. Lightweight camping tents use a "rain fly" that has 2 functions. One is to be waterproof, with the tent itself underneath having a permeable surface so human moisture (breathing, sweating) can disperse. The other is to serve as a radiant heat shield. Surfaces radiate heat toward cold dark areas--it's why we get dew on the truck at night, or in this season we in Michigan have really low nighttime temps when the sky is clear. The truck and the earth radiate heat toward the cold dark sky. Clouds, or the rain fly, interrupt that and keep things warmer. So bringing in air at night may be counterproductive if the hull, decks, and overhead are cold. They may just serve as condensing surfaces. My other boat has a big boom tent cover to protect the mahogany and spruce. But it also has the same effect as the camping tent's rain fly--it serves as a radiant heat barrier. I get a lot more mildew on the overhead where the cover isn't than where it is. That boat is passively and incompletely ventilated. Chris Campbell

The accuracy of cheap hygrometers is not very good but here is a trick to get an accurate one. They probably hit the shelf with some tolerance, say +-5 percent. I went to Lowes and looked at all the ones in the box and picked the one that was right in the middle so if they were reading 55 to 65, I bought the one that read 60. It agreed perfectly with the expensive digital one I subsequently bought. The one that came in my nice yacht thermometer, hygrometer, barometer from West Marine was off about 30 percent. Allen On Wed, Jan 31, 2018 at 12:20 PM, Jim Englert <sa… [at] gmail.com> wrote: > > A hygrometer is about $10 and would let you know how successful your > venting was. > > > On Jan 31, 2018, at 11:50 AM, Allen Edwards al… [at] gmail.com > [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > > With all due respect, I think you are more likely to get condensation with > warm air than with cold. In my example with 68F air at 75% the dew point > is 60F so that air hitting the 55 degree hull would condens out where the > 52 degree air at 90% would not because the dew point is 43 F. That is why > given the choice I would rather vent with the cold relatively dry air even > though it has a higher RH. But as I am not going to install dampers and > vapor pressure monitors, I just vent. If I were in Florida, I would get a > dehumidifier. > > Allen > > On Wed, Jan 31, 2018 at 8:02 AM, ccampbell cc… [at] lsnm.org [Cal_Boats] > <Ca… [at] yahoogroups.com> wrote: > >> >> >> >> >> On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net [Cal_Boats] wrote: >> >> In our experience in the 15+ yrs we have owned our Cal in NC, solar vents >> work best. We installed solar vents 1st. Replaced them with 24hr vent when >> they wore out. Replace the 24hr vents with solar when they quit working. >> >> The 24 hr vents allowed the mold to grow faster. The solar only brought >> in dryer air. Weather here in NC is “clear and cold, or warm and rain”. >> >> >> One issue is the temp of surfaces. Moisture tends to condense out on >> cold surfaces. Lightweight camping tents use a "rain fly" that has 2 >> functions. One is to be waterproof, with the tent itself underneath having >> a permeable surface so human moisture (breathing, sweating) can disperse. >> The other is to serve as a radiant heat shield. Surfaces radiate heat >> toward cold dark areas--it's why we get dew on the truck at night, or in >> this season we in Michigan have really low nighttime temps when the sky is >> clear. The truck and the earth radiate heat toward the cold dark sky. >> Clouds, or the rain fly, interrupt that and keep things warmer. So >> bringing in air at night may be counterproductive if the hull, decks, and >> overhead are cold. They may just serve as condensing surfaces. >> >> My other boat has a big boom tent cover to protect the mahogany and >> spruce. But it also has the same effect as the camping tent's rain fly--it >> serves as a radiant heat barrier. I get a lot more mildew on the overhead >> where the cover isn't than where it is. That boat is passively and >> incompletely ventilated. >> >> Chris Campbell >> >> >> >> >> > > >

On 1/31/2018 5:26 AM, Jim Englert sa… [at] gmail.com [Cal_Boats] wrote: > > > > Mold tends to grow when the Relative humidity is over 60%. Depending > on the area, ventilation may or may not help much. If the boat is in > water that is cold and the outside air is warm, if enough air is not > brought in to raise the temp of the boat and or the outside air has a > high relative humidity, bringing outside air in can actually increase > the relative humidity. I can always tell when humidity hits here in the summer. My Cal 20 lies on a mooring in a shallow near-shore area of deep Grand Traverse Bay. When the air is humid, and when the wind has been offshore so as to bring in cold deep water, I get lots of condensation inside the hull below waterline. Not just damp-ish... I mean puddles. Ventilation won't help that at all. I wait for dryer air and warmer surface water to accumulate. Chris Campbell > >

I like this tip of underlayment, but I accomplish the same thing by propping my cushions up every time I leave the boat. That way nothing is trapped under the cushions. We have done two things to prevent mildew and mold that have worked well besides propping up the cushions. We have two dorade vents on the deck and I always leave one facing aft and one facing forward. That way, no matter the wind direction, one is an exhaust vent and one is an intake — keeps air turning over below decks. Then, we have two low wattage heaters — one in the v-berth and one in the galley that warm the air just enough to keep it circulating. These were all tips from the veteran boater who sold us the boat and it has worked well to keep the inside of the boat dry and we have been in Gulf Coast humidity, Chesapeake Bay humidity and freezing winters, and northwest perpetually rainy winters. Don Dutton 1986 Cal 33-2, “Quantum Evolution” Hayden Island, Oregon > On Jan 31, 2018, at 12:25 PM, Helen Horn he… [at] sbcglobal.net [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > If you have not already done so, I suggest installing an underlayment of elevated hard plastic or rubber grid squares beneath your bunk mattresses. We have done this, as well as gone one square up the sides so the bedding doesn't touch the hull and air can flow under and around. It helps a lot, and bedding stays drier from not soaking side condensation. I bought a number of 40 square foot boxes of this decking type stuff. But I am in California. I also washed down a bit of mildew on our trawler last year, then put a mildew preventer on after, it seems to be working. Going to use on cal 36 this year. But it's nasty smelling for a day or two, don't inhale. I'm not sure about safety after it dries, as obviously it's toxic to mold. Helen > > > Sent from Yahoo Mail on Android <https://overview.mail.yahoo.com/mobile/?.src=Android> > On Wed, Jan 31, 2018 at 11:05 AM, Allen Edwards al… [at] gmail.com [Cal_Boats] > <Ca… [at] yahoogroups.com> wrote: > > > With all due respect, I think you are more likely to get condensation with warm air than with cold. In my example with 68F air at 75% the dew point is 60F so that air hitting the 55 degree hull would condens out where the 52 degree air at 90% would not because the dew point is 43 F. That is why given the choice I would rather vent with the cold relatively dry air even though it has a higher RH. But as I am not going to install dampers and vapor pressure monitors, I just vent. If I were in Florida, I would get a dehumidifier. > > Allen > > On Wed, Jan 31, 2018 at 8:02 AM, ccampbell cc… [at] lsnm.org <mailto:cc… [at] lsnm.org> [Cal_Boats] <Ca… [at] yahoogroups.com <mailto:Ca… [at] yahoogroups.com>> wrote: > > > > > On 1/31/2018 8:30 AM, John Raxter jr… [at] att.net <mailto:jr… [at] att.net> [Cal_Boats] wrote: >> In our experience in the 15+ yrs we have owned our Cal in NC, solar vents work best. We installed solar vents 1st. Replaced them with 24hr vent when they wore out. Replace the 24hr vents with solar when they quit working. >> >> The 24 hr vents allowed the mold to grow faster. The solar only brought in dryer air. Weather here in NC is “clear and cold, or warm and rain”. > > One issue is the temp of surfaces. Moisture tends to condense out on cold surfaces. Lightweight camping tents use a "rain fly" that has 2 functions. One is to be waterproof, with the tent itself underneath having a permeable surface so human moisture (breathing, sweating) can disperse. The other is to serve as a radiant heat shield. Surfaces radiate heat toward cold dark areas--it's why we get dew on the truck at night, or in this season we in Michigan have really low nighttime temps when the sky is clear. The truck and the earth radiate heat toward the cold dark sky. Clouds, or the rain fly, interrupt that and keep things warmer. So bringing in air at night may be counterproductive if the hull, decks, and overhead are cold. They may just serve as condensing surfaces. > > My other boat has a big boom tent cover to protect the mahogany and spruce. But it also has the same effect as the camping tent's rain fly--it serves as a radiant heat barrier. I get a lot more mildew on the overhead where the cover isn't than where it is. That boat is passively and incompletely ventilated. > > Chris Campbell >> >> > > > > >

On 1/31/2018 3:40 PM, Allen Edwards al… [at] gmail.com [Cal_Boats] wrote: > > > The accuracy of cheap hygrometers is not very good but here is a trick > to get an accurate one. They probably hit the shelf with some > tolerance, say +-5 percent. I went to Lowes and looked at all the > ones in the box and picked the one that was right in the middle so if > they were reading 55 to 65, I bought the one that read 60. It agreed > perfectly with the expensive digital one I subsequently bought. The > one that came in my nice yacht thermometer, hygrometer, barometer from > West Marine was off about 30 percent. It's probably adjustable if you want to make it more accurate. A little disassembly.... Set it when the humidity is in the middle of your usual range and it will probably be accurate enough. Chris Campbell > >

Oye vey, Reggie! That's terrible. I once had a plywood catamaran that not only got mold, but massive wood eating fungus which destroyed in in one winter. HORRIBLE!. The air in the boat will heat up during the day, sucking in moisture, since hot air holds more water vapor. At night the interior will get cold, and all the moisture will precipitate out as water droplets all over the interior surfaces, particularly the overhead and bulkheads/hull interior where it's coldest. Between that, dust, bacteria (I used to date two girls at the same time in Grad school. One was a nursing student, the other was a microbiologist. The nursing student had a nickname for her rival. She called her "Bacteria". Sadly, Bacteria (of course, I can't remember her real name now) became horribly allergic to formalin-used to fix samples, almost died, ending her career. Hex? And the nursing student got married to someone else, had kids and I assume, lived happily ever after). Oh yes, I almost forgot. Ventilation. I think the good thing about ventilation during the day is it holds down the heat inside the boat, reducing intake of water vapor, and ventilating at night probably helps the water droplets evaporate, hopefully before all of it precipitates all over the boat's interior. And of course, those solar vents probably work well, or, solar coupled with batteries and a vent fan as well.Jerry of Shpritz On Thursday, February 1, 2018 6:40 AM, "ccampbell cc… [at] lsnm.org [Cal_Boats]" <Ca… [at] yahoogroups.com> wrote: On 1/31/2018 3:40 PM, Allen Edwards al… [at] gmail.com [Cal_Boats] wrote: The accuracy of cheap hygrometers is not very good but here is a trick to get an accurate one. They probably hit the shelf with some tolerance, say +-5 percent. I went to Lowes and looked at all the ones in the box and picked the one that was right in the middle so if they were reading 55 to 65, I bought the one that read 60. It agreed perfectly with the expensive digital one I subsequently bought. The one that came in my nice yacht thermometer, hygrometer, barometer from West Marine was off about 30 percent. It's probably adjustable if you want to make it more accurate. A little disassembly.... Set it when the humidity is in the middle of your usual range and it will probably be accurate enough. Chris Campbell