You can get tables or charts like this:
http://www.lordgrey.org.uk/~f014/usefulresources/aric/Resources/Teaching_Packs/Key_Stage_4/Weather_Climate/images/02d.jpg
How you read it?
- Check 25degC - see the line is at about 23g/m3
This means at 25degC the air can contain maximum 23g/m3 vapour. This is
100% rel. humidity. 70% relH means you have about 16g/m3 absolute water in
the air (at 25degC)
- Chech 10degC - see the line is at about 9g/m3
This means at 10degC the air can contain max 9g/m3 (at 100%relH), the rest
will condense. So if you cool your air to 10degC, the diff (7g) will
condense.
(I was using a different table in the morning for my calculation, hence the
difference. You may find absolute/relative humidity calculators on the web,
that are more accurate than such a chart)
Vajk
On Tue, Jul 9, 2013 at 5:14 PM, Peter Hollenbeck <[email protected]> wrote:
> Is there a formula behind "seal 25Celsius 70% humidity air in, and cool
> that down to 10Celsius, you will have about 9grams of condensation per
> cubic meter"?
>
> Volume of the largest bilge compartment is about 6 cu. ft. or roughly 0.2
> cu. meter., so about 2 grams condensation.
>
> Typical warm July, afternoon about 20C. Could be warmer in September when
> we are likely to be gluing in the flooring.
>
> I thanks everyone for the ideas.
> Peter
>
>
> On Mon, Jul 8, 2013 at 11:31 PM, Vajk Fekete <[email protected]> wrote:
>
>> If you seal 25Celsius 70% humidity air in, and cool that down to
>> 10Celsius, you will have about 9grams of condensation per cubic meter of
>> air.
>>
>> In my view this is not too significant. You only will have problems, if
>> fresh humid air can enter, and more water condensens from the fresh air.
>>
>> You can consider adding some silica gel (the one in inslulated window
>> glass panel frames) to the cavity.
>>
>> Vajk
>>
>>
>> On Tue, Jul 9, 2013 at 12:35 AM, Peter Hollenbeck <[email protected]>wrote:
>>
>>> Good points.
>>> All surfaces have at least two coats of epoxy. We may glass the interior
>>> surfaces as we have the exterior of the hull. If we use glass on all
>>> surfaces the process is: apply a thin seal coat of epoxy. Dry. apply
>>> another coat of epoxy, then immediately the glass, followed by a liberal
>>> coat of epoxy to saturate the glass and adhere it to the sealed plywood.
>>> Exterior surfaces have more epoxy to give a smooth base for paint.
>>>
>>> My 1wire system tells me the humidity 6AM to 3PM today is 53 to 80%,
>>> even though it is a nice sunny day. This because we are about 20 feet from
>>> the ocean water of the British Columbia Inside Passage and 30 feet the
>>> other way to the B.C. woods. So yes, we will have sealed in moisture and I
>>> thank you for pointing this out.
>>>
>>> When in the water the bilge should be quite cool, as the water
>>> temperature is about 10C year round. I don't know what bearing this has.
>>>
>>> Will I not have a baseline to measure against? Let's say the humidity is
>>> 70% when the bilge is sealed. I would take readings then and again after
>>> the boat is launched. Periodically thereafter I would take additional
>>> reading and expect them to be in the range of the original ones.
>>>
>>> I say again, OWFS is a great project with great participants. I follow
>>> the list and try to learn from it but sometimes don't understand a word.
>>> Thanks, Paul.
>>> Thanks, everyone.
>>>
>>>
>>>
>>> On Mon, Jul 8, 2013 at 11:20 AM, Don Veino <[email protected]>wrote:
>>>
>>>> Looks like you have a nice project going. However, I'm going to guess
>>>> that no matter what you do, you are going to have liquid water inside the
>>>> compartments if you seal them shut.
>>>>
>>>> Why? Unless you are building the boat in a desert in winter, you will
>>>> be sealing in relatively warm and humid air inside the compartments. When
>>>> the boat is in the water, the compartments will cool and the moisture will
>>>> condense.
>>>>
>>>> Depending on the size of the compartments, the amount of liquid water
>>>> could be a few drops to something more significant.
>>>>
>>>> I'm projecting your construction technique to mean exterior epoxy
>>>> coating but likely not interior to the compartments. If so, then you have
>>>> the opportunity for interior rot with water contacting bare wood.
>>>>
>>>> I built a small trailer with similar construction that was very air
>>>> tight and ended up adding vents and a drain plug for this and other
>>>> reasons. And yes, I did play with the idea of installing a 1-wire network
>>>> in the trailer to monitor conditions and control some stuff. :)
>>>>
>>>>
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