Warming the air increases its ability to hold water, therefore the relative humidity will decrease as the air warms.
When the air cools, its ability to hold water decreases, raising the relative humidity. Thus, humidity is relative to the temperature. This is why weather forecasters have switched from telling us the relative humidity to telling us the dew point, a more useful piece of information. When air temperature falls to the dew point it is holding all the water it can. If it cools any more fog and dew will result as water condenses from vapor to liquid. More to our point, any object (portholes, hatches, etc) inside a boat that have a temperature lower than the dew point inside your boat will condense water on them. You can measure dew point with a sling hygrometer, basically two thermometers, one wet and one dry, that you swing rapidly around. The difference in the two temperatures in the breeze can tell you the dew point. Electric space heaters heat both the air and the moisture in the air by contact with the hot (or warm) parts, whether using a fan or natural convection flow. Warm objects also radiate infrared radiation that is absorbed by whatever objects absorb the radiation. The main difference between cube heaters (including all the pricey variations) and the radiators is that the cubes are small, have a noisy fan, produce rapid warmth and because the hot part is concentrated can set things on fire and are easy to store. The radiators are large, silent, slow to heat and because the hot part is spread out, safe from fire and take up much more space. They both can produce the same amount of heat, 1500 watts max. It has been the collective opinion of the List over the years that the best, and most expensive (surprise, surprise!), system is hydronic or circulating hot water. Every year about this time there appears a thread about heat, humidity and condensation inside boats in northern climates. Unfortunately, the most satisfactory solution is also the most difficult (expensive, troublesome). Recall that any object whose temperature is below the dew point will create dew (circular definition?). That is to say, every object or material inside your boat that has a temperature below the dew point of the air inside your boat WILL become wet. You can lower the dew point of the air inside your boat, or your can raise the temperature of the surfaces inside your boat. NOTHING ELSE will do the job. You are dealing with laws of nature. The are called LAWS of nature for a reason. Raising the air temperature will not affect the dew point. The relative humidity will rise and he air will feel drier, but objects below the dew point will still get wet, i.e. Kool-Aid pitchers on a summer day. Aboard Bandersnatch, because I built her myself, I had the opportunity of installing insulation before or while I built the joinery so the living quarters are insulated with two to three inches of foam. The only places I have condensation is the windows near the berth which we deal with by sopping up the water daily with paper towels. You can install insulation on your boat and because the inside surface of the insulation is the same temperature as the air inside the boat you will not have condensation, however, any objects the insulation is covering, if the interior air can get there, will be wet. I have found Damp Rid to be useful for removing small amounts of water over long periods from seldom opened spaces, such as hanging lockers and other storage areas. Perhaps if you could make air-tight foam boxes duct-taped around cold places such as skylights and portholes, you could put a Damp Rid bucket in there and dry out the space. We do not heat the boat, we go south and put on more clothes. Norm S/V Bandersnatch Lying Julington Creek FL N30 07.68 W081 38.47 > What I understand is that it doesn't dry the air but uses the humidity to help transport the heat to those spots around the room /boat _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://liveaboardonline.com/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
