A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat


i.e. http://www.tlc-direct.co.uk/Products/PHTH1.html

with for example a http://www.tlc-direct.co.uk/Products/TCWS10.html



I suppose the key thing will be what temperature you set them to switch on ?
.... somebody mentioned the heaters need to keep above the dew point ? ......
well in practice what temp is that for UK ?

I did have a Google to look at this, but explanation did not help much
http://en.wikipedia.org/wiki/Dew_point

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?


Anybody care to shed some light on this.

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?


Anybody care to shed some light on this.






Http://www.bbc.co.uk/weather/weather...precipitation_
dewandfrost.shtml


or...

http://www.faqs.org/faqs/meteorology/temp-dewpoint/


you might have to copy and paste that to get it to open....
--
Tony Sayer

In article ,
"Rick Hughes" writes:
A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat


i.e. http://www.tlc-direct.co.uk/Products/PHTH1.html

with for example a http://www.tlc-direct.co.uk/Products/TCWS10.html



I suppose the key thing will be what temperature you set them to switch on ?
... somebody mentioned the heaters need to keep above the dew point ? ......
well in practice what temp is that for UK ?

I did have a Google to look at this, but explanation did not help much
http://en.wikipedia.org/wiki/Dew_point

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?

It's not a fixed temperature, unfortunately, so that won't work.
Leaving the heater on all the time will always reduce the
relative humidity in the boat (because relative humidity drops
with increasing temperature at a fixed absolute humidity). This
will waste power when the outside humidity is high enough that
you aren't near the dew point (relative humidity of 100%).

What you need to do is ventilate under the covers, and apply
heating when the outside humidity is near 100%. Trouble is that
measuring humidity accurately near the extremes is difficult,
and most humidity sensors won't work there. I can't think of a
good answer.

The other thing I would warn about is that messing with humidity
can have a nasty effect on timber. If you do reduce on one side of
a piece of timber verses the other, the timber will cup across the
grain. In a house, you can get cupped floorboards which pull out
the nails by running a dehumidifier in a room. In a boat, I could
imagine much more dire consequences such as wrecking the hull, but
I'm not a boating person.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:
In article ,
"Rick Hughes" writes:

A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat


i.e. http://www.tlc-direct.co.uk/Products/PHTH1.html

with for example a http://www.tlc-direct.co.uk/Products/TCWS10.html



I suppose the key thing will be what temperature you set them to switch on ?
... somebody mentioned the heaters need to keep above the dew point ? ......
well in practice what temp is that for UK ?

I did have a Google to look at this, but explanation did not help much
http://en.wikipedia.org/wiki/Dew_point

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?

It's not a fixed temperature, unfortunately, so that won't work.
Leaving the heater on all the time will always reduce the
relative humidity in the boat (because relative humidity drops
with increasing temperature at a fixed absolute humidity). This
will waste power when the outside humidity is high enough that
you aren't near the dew point (relative humidity of 100%).

What you need to do is ventilate under the covers, and apply
heating when the outside humidity is near 100%. Trouble is that
measuring humidity accurately near the extremes is difficult,
and most humidity sensors won't work there. I can't think of a
good answer.

The other thing I would warn about is that messing with humidity
can have a nasty effect on timber. If you do reduce on one side of
a piece of timber verses the other, the timber will cup across the
grain. In a house, you can get cupped floorboards which pull out
the nails by running a dehumidifier in a room. In a boat, I could
imagine much more dire consequences such as wrecking the hull, but
I'm not a boating person.

120w will make so little difference to temp that its quite pointless
controlling them thermostatically. If you want to go down that path,
just leave em on whenever theres a risk of damp. I really cant see a
degree or 2 solving anything though.

If you want dryness, you want a dehumidifier. But as Andrew says, what
effect over-use of one could hahve on the timber I've no idea. IOW it
must be humidistatic, and set correctly.

BTW the drying effect of heating is a bit more complex. When
heated, the air RH drops, and both lower RH and higher temp increase
the evaporation rate of damp sources, resulting in a higher level of
damp in the air than before. As air exchanges between inside and out,
the net effect of this exchange is to carry moisture out of the
building. With CH this stays true even in a wet cold winter - although
RH can reach 100% outside, there is still more water per cube in nice
dry warm indoor air, so air exchange still dries the building.


NT

"Andrew Gabriel" wrote in message
...
In article ,
"Rick Hughes" writes:
A question came up on an on-line boating forum ... about putting a couple
of
tubular (60W) heaters in a boat, to try and keep things dry under the
boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat
sensors won't work there. I can't think of a
good answer.

The other thing I would warn about is that messing with humidity
can have a nasty effect on timber. If you do reduce on one side of
a piece of timber verses the other, the timber will cup across the
grain. In a house, you can get cupped floorboards which pull out
the nails by running a dehumidifier in a room. In a boat, I could
imagine much more dire consequences such as wrecking the hull, but
I'm not a boating person.


No timber at all on this boat.

In any event I don't want to reduce boat to biscuit dryness ... just enough
to keep things dry & condensation free (& hence mould)

I appreciate what you have said, but I'm no closer to the answer as to what
temp should I start heating at ? ... i.e. to set a frost stat ....

I don't want something complex, I thought there might be a simple answer
obviously not.


have to see if I can find a combined humidistat / thermostat ... but
guessing nothing in price range I'll want to pay.

"tony sayer" wrote in message
...
I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?


Anybody care to shed some light on this.






Http://www.bbc.co.uk/weather/weather...precipitation_
dewandfrost.shtml

Well I followed the first one ... i.e.
"Even the driest air contains some water vapour. The condensation process is
the same whether we talk about dew or cloud. However, if the air is cooled
sufficiently, at night for instance, some of the water vapour will condense
on surfaces as dew. The temperature at which air, at a level of constant
pressure, can no longer hold all the water it contains is called the dew
point. However, when a sample of air is lifted up through cooling air to a
level at which is condenses, we use the term condensation level instead of
dew point"


The second link was akin to an undergraduate maths thesis ....

Rick Hughes wrote:

"Andrew Gabriel" wrote in message
...
In article ,
"Rick Hughes" writes:
A question came up on an on-line boating forum ... about putting a
couple of
tubular (60W) heaters in a boat, to try and keep things dry under the
boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat
sensors won't work there. I can't think of a
good answer.

The other thing I would warn about is that messing with humidity
can have a nasty effect on timber. If you do reduce on one side of
a piece of timber verses the other, the timber will cup across the
grain. In a house, you can get cupped floorboards which pull out
the nails by running a dehumidifier in a room. In a boat, I could
imagine much more dire consequences such as wrecking the hull, but
I'm not a boating person.


No timber at all on this boat.

In any event I don't want to reduce boat to biscuit dryness ... just
enough to keep things dry & condensation free (& hence mould)

I appreciate what you have said, but I'm no closer to the answer as to
what temp should I start heating at ? ... i.e. to set a frost stat ....

I don't want something complex, I thought there might be a simple answer
obviously not.


have to see if I can find a combined humidistat / thermostat ... but
guessing nothing in price range I'll want to pay.

I'm not at all convinced that you should do any heating at all. Have you
actually tried simply running a small fan - with simple ducting if required?

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On Nov 13, 2:37*pm, "Rick Hughes" wrote:
A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat

i.e.http://www.tlc-direct.co.uk/Products/PHTH1.html

with for example ahttp://www.tlc-direct.co.uk/Products/TCWS10.html

I suppose the key thing will be what temperature you set them to switch on ?
... somebody mentioned the heaters need to keep above the dew point ? .......
well in practice what temp is that for UK ?

I did have a Google to look at this, but explanation did not help muchhttp://en.wikipedia.org/wiki/Dew_point

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?

Anybody care to shed some light on this.

An incandesant 100w bulb is a 96 watt heater, dew point varies with
humidity and temp. There are low temp 40f dehumidifiers. A
dehumidifier itself may generate enough heat if its tight to raise
temp 10-15f. In a 600 sq ft basement mine raises temp 3-4f

In article , Rick Hughes
scribeth thus

"tony sayer" wrote in message
...
I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?


Anybody care to shed some light on this.






Http://www.bbc.co.uk/weather/weather...precipitation_
dewandfrost.shtml

Well I followed the first one ... i.e.
"Even the driest air contains some water vapour. The condensation process is
the same whether we talk about dew or cloud. However, if the air is cooled
sufficiently, at night for instance, some of the water vapour will condense
on surfaces as dew. The temperature at which air, at a level of constant
pressure, can no longer hold all the water it contains is called the dew
point. However, when a sample of air is lifted up through cooling air to a
level at which is condenses, we use the term condensation level instead of
dew point"


The second link was akin to an undergraduate maths thesis ....


Well it did come off this site)...

http://www.cl.cam.ac.uk/research/dtg/weather/

refer to the line;

"If you're wondering exactly what the "Dew Point" is, look here for a
simple explanation, or here for more than you could possibly want to
know"
--
Tony Sayer

ransley wrote:
On Nov 13, 2:37�pm, "Rick Hughes" wrote:
A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat

i.e.http://www.tlc-direct.co.uk/Products/PHTH1.html

with for example ahttp://www.tlc-direct.co.uk/Products/TCWS10.html

I suppose the key thing will be what temperature you set them to switch on ?
... somebody mentioned the heaters need to keep above the dew point ? .......
well in practice what temp is that for UK ?

I did have a Google to look at this, but explanation did not help muchhttp://en.wikipedia.org/wiki/Dew_point

I guess what we would need to know for a simple thermostat controlled
installation (ignoring hygrometers and integrating controllers) that there
should be a minimum dew point for a typical range of UK temperature &
Humidity.

almost a 'set it to this' and it will always be above the dew point ?

Anybody care to shed some light on this.

An incandesant 100w bulb is a 96 watt heater, dew point varies with
humidity and temp. There are low temp 40f dehumidifiers. A
dehumidifier itself may generate enough heat if its tight to raise
temp 10-15f. In a 600 sq ft basement mine raises temp 3-4f

yes for those temps you'd need an ansorption wheel dehumidifier


NT

On Thu, 13 Nov 2008 20:37:02 -0000, "Rick Hughes"
wrote:

A question came up on an on-line boating forum ... about putting a couple of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat

If you have the space then just mount a normal mains dehumidifier high
up and drain it over the side, leave it set on a low setting - it will
consume next to bugger all power and do a better job as it keeps the
air moving round the cabin. Open all the access panels into the bilge
as well as the engine, If the boat is still on the water sling a
bucket of jeyes fluid and water into the bilge, go for a run and let
it slosh around to freshen things up.

It's also worthwhile wiping down all surfaces with a bicarb solution,
remove any soft furnishings to store in a spare room at home.

Check your sea cocks, and then check them again


--

On 13 Nov, 20:37, "Rick Hughes" wrote:

should be a minimum dew point for a typical range of UK temperature &
Humidity.

No such (useful) critter, as it varies too much.

A better rough guide is to keep the temperature of likely condensing
surfaces slightly above the temperature of the warmest incoming air
(i.e. a constant temperature difference, not a constant temperature).
You ought to find that leaving a constant heater power switched on,
possibly through a timeswitch, is adequate to achieve this without any
active controls at all. Can't estimate the power though, without
knowing volumes, areas and insulation quality.

Condensation doesn't happen randomly, it happens when moist air at one
temperature (at which it can carry that moisture) is cooled down to a
temperature at which the RH would exceed 100%. So long as the air
remains above this first temperature, you're OK. You might even drop
slightly below it, by an amount dependent on how far the incoming air
is from saturation.

Hoadley's "Understanding Wood" is a fine book and amongst other things
has an excellent chapter on humidity-related issues.

On Thu, 13 Nov 2008 22:31:23 +0000, Rick Hughes wrote:

No timber at all on this boat.

In any event I don't want to reduce boat to biscuit dryness ... just enough
to keep things dry & condensation free (& hence mould)

Well in that case a dehumidifier would do the job. All you'd have to do is
empty the condensate collection trough out as necessary (unless you could
drain it to outside).


I don't want something complex, I thought there might be a simple answer
obviously not.

A dehumidifier is simple. It's simply about £80-100 :-)


--
John Stumbles

I can't stand intolerance

"John Stumbles" wrote in message
...
On Thu, 13 Nov 2008 22:31:23 +0000, Rick Hughes wrote:

No timber at all on this boat.

In any event I don't want to reduce boat to biscuit dryness ... just
enough
to keep things dry & condensation free (& hence mould)

Well in that case a dehumidifier would do the job. All you'd have to do is
empty the condensate collection trough out as necessary (unless you could
drain it to outside).


I don't want something complex, I thought there might be a simple answer
obviously not.

A dehumidifier is simple. It's simply about £80-100 :-)


This was discussed on another forum ... but the consensus of the guys there
was that unless you can enclose your boat in an airtight bag ... the
humidifier will just keep sucking moisture out of the external mass of air
....
One US company did sell a complete over bag, came up and over like the rain
hood on a pram ... floor to floor rubber seals.
Way too expensive though.

"Mike" wrote in message
...
On Thu, 13 Nov 2008 20:37:02 -0000, "Rick Hughes"
wrote:

A question came up on an on-line boating forum ... about putting a couple
of
tubular (60W) heaters in a boat, to try and keep things dry under the boat
covers, and engine hatch over winter.
Controlling them using a simple frost stat

If you have the space then just mount a normal mains dehumidifier high
up and drain it over the side, leave it set on a low setting - it will
consume next to bugger all power and do a better job as it keeps the
air moving round the cabin. Open all the access panels into the bilge
as well as the engine, If the boat is still on the water sling a
bucket of jeyes fluid and water into the bilge, go for a run and let
it slosh around to freshen things up.

It's also worthwhile wiping down all surfaces with a bicarb solution,
remove any soft furnishings to store in a spare room at home.

Check your sea cocks, and then check them again


Do you know of any such units ? ..... seen the B&Q items and discounted
those

Air flow and removing moisture might be the way to go rather than heat.

AJH wrote:

As you have noted a problem then we already know ventilation is an
issue, if ventilation allowed air changes fast enough that the
internal air remained in equilibrium with external air and there are
no leaks then there would be no condensation.

This turns out not to be the case After all, I get condensation on my
lawn most mornings this time of year...

You need to keep the dew point below the temp. of the things inside your
boat. A dehumidifier is the solution that will use least power; a
heater will use more power, but cost less to buy. Your call!

Andy

On 14 Nov, 19:05, "Rick Hughes" wrote:

This was discussed on another forum ... but the consensus of the guys there
was that unless you can enclose your boat in an airtight bag ... the
humidifier will just keep sucking moisture out of the external mass of air
...
One US company did sell a complete over bag,

We were in Barcelona in April. The harbour was full of million dollar
gin palaces having their winter bags peeled off, ready for the season

In article ,
Andy Champ writes:
AJH wrote:

As you have noted a problem then we already know ventilation is an
issue, if ventilation allowed air changes fast enough that the
internal air remained in equilibrium with external air and there are
no leaks then there would be no condensation.

This turns out not to be the case After all, I get condensation on my
lawn most mornings this time of year...

Your lawn radiates its heat into outer space, and hence
gets colder than the air temperature at various points
overnight, thus the formation of dew. The cover will
protect the boat from this to some extent (a thermal
insulating cover would be ideal). Can also be caused
by air colling below its dewpoint and forming mist,
some of which will settle out on the ground.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 15 Nov, 14:59, AJH wrote:

So cut the air changes and set the
dehumidifier at a moderate level and it doesn't have to work too hard.

Although a refrigeration dehumidifier (the affordable sort) is
uselessly inefficient for unheated spaces in winter.

Andrew Gabriel wrote:

Your lawn radiates its heat into outer space, and hence
gets colder than the air temperature at various points
overnight, thus the formation of dew. The cover will
protect the boat from this to some extent (a thermal
insulating cover would be ideal). Can also be caused
by air colling below its dewpoint and forming mist,
some of which will settle out on the ground.


I don't know what his boat is made of, but I'm pretty sure it too will
be exposed to the cold night sky. A cover will reduce the heat loss,
but it will still be there; if you get a switch from warm, moist air to
cold, such as we just have, there will be condensation.

If you truly want no condensation you want to seal it, and keep the
temperature of everything inside the sealed area above the dew point.
Since this is likely to include some substantial bits of metal (Engine?
Keel?) and possibly contact with a large, cold body of water, reducing
humidity may well be the only answer.

Blowing lots of warm damp air on a foggy morning over a deckhead that
has been exposed to the midnight sky is not a recipe to prevent
condensation.

Andy