incognito
N/A
I have read this thread with amusement and disbelief.
The theorists about the atmospheric behaviour inside boats have a lot to learn, and the experiments are misleading. The only way to prove things is to do them and see what happens.
First, the DH... they work by pretending to be fridges, and we know that the moisture in a fridge ices up on the element - that is how they work. However, that just produces ice, which is OK for the drinks, but will just make the boat heavier. The cheaper DH will switch off the fridge, and rely on ambient temperature to defrost the element into the draining arrangements. This is OK unless you want the thing to work below freezing. (See heater comments as to why this may be OK).
The more expensive DH will reverse the fridge cycle, and defrost the element not relying on ambient temperature.
We have an expensive DH from CruiserMart, cost about £299, I think, but that was cos I had not done my homework, I believe the B&Q version would be just as good at £99, but I have never seen it so don't know.
Now, this is our third year with a DH, and this is how it is for us (NOT a theory).
Current boat 36ft (previous was somewhat smaller). Following applies from about October to April.
When leaving boat after sailing or check-visit. All ventilators shut, as I don't want to DH the whole world! No special sealing of the normal atmospheric leakage. Engine access open with small greenhouse (non-fan) heater set to come on at low temp in close proximity to engine bay. DH set to 70% Rh (mine is settable and has a continuous setting, but never used it, puts elec.bill up). Most clothing and bedding removed from normal storage and placed on berths (probably unnecessary). All sea-cocks closed except kitchen sink. DH stood on draining-board beside sink, with a little tilt to the left (otherwise the built-in tank takes priority and turns DH off when full) and drain tube led to sink. Greenhouse Min/Max thermometer placed judiciously away from heater and DH.
Results: everything stays dry and nice-smelling. Normally, when you pick up something which is cold, then any dampness makes it FEEL cold and damp. We do not have that, all our cold stuff feels cold and dry and instantly warms up under our touch (try it yourself on your boat!). We used to get light mildew up in the hatches, where the relatively warmer air (heated by the seawater) condensed out on the hatch-glazing. We also used to get condensation all year round under berth cushions, after a good night's sleep, always had dampness under cush. We have neither of these symptoms anymore (even in season, never dampness under berths).
Max/Min never goes below zero, even though only 500W greenhouse heater (which means the DH could be a cheaper version, see above). I think this suggests that I am not exchanging my internal air much with the outside.
Finally... we reach September with some water in the bilges, below strum box pick up. By the end of October, mid November, our bilges are dry, although the bottom of the bilge is nearly 6ft below the DH.
I am not good on theories, but maybe the seawater heats the air, relatively, and causes a natural convection - maybe it is the blower in the DH? I don't know, but I have told you the way it is, not the way I think it might be.
I note what someone posted about ventilation - on our 23ft Sonata we used to rely on ventilation - standing all our berth cushions on one edge when leaving, to allow clear air flow... NEVER ENOUGH!!! The cold damp air of the Medway would come in and set up a high Rh, and each spring we had smelly everything. I think this was amplified by the fact that the moisture brought into the boat during the sailing season was soaked up by all the boat's fabric and never really dried before the winter (maybe, I don't know, just another untried theory!!).
A point about quantity of water extracted.. before we discovered about the tilt needed to prioritise the external drain, we left the machine unattended for a fortnight or three weeks, and when we came back, the machine had filled its tank and switched off. I think the tank must hold 2 litres (but that is a guess, I can't remember).
I have no experience of the dehumidifier crystals, but they certainly sound much cheaper than a DH machine, if they work for you.
The theorists about the atmospheric behaviour inside boats have a lot to learn, and the experiments are misleading. The only way to prove things is to do them and see what happens.
First, the DH... they work by pretending to be fridges, and we know that the moisture in a fridge ices up on the element - that is how they work. However, that just produces ice, which is OK for the drinks, but will just make the boat heavier. The cheaper DH will switch off the fridge, and rely on ambient temperature to defrost the element into the draining arrangements. This is OK unless you want the thing to work below freezing. (See heater comments as to why this may be OK).
The more expensive DH will reverse the fridge cycle, and defrost the element not relying on ambient temperature.
We have an expensive DH from CruiserMart, cost about £299, I think, but that was cos I had not done my homework, I believe the B&Q version would be just as good at £99, but I have never seen it so don't know.
Now, this is our third year with a DH, and this is how it is for us (NOT a theory).
Current boat 36ft (previous was somewhat smaller). Following applies from about October to April.
When leaving boat after sailing or check-visit. All ventilators shut, as I don't want to DH the whole world! No special sealing of the normal atmospheric leakage. Engine access open with small greenhouse (non-fan) heater set to come on at low temp in close proximity to engine bay. DH set to 70% Rh (mine is settable and has a continuous setting, but never used it, puts elec.bill up). Most clothing and bedding removed from normal storage and placed on berths (probably unnecessary). All sea-cocks closed except kitchen sink. DH stood on draining-board beside sink, with a little tilt to the left (otherwise the built-in tank takes priority and turns DH off when full) and drain tube led to sink. Greenhouse Min/Max thermometer placed judiciously away from heater and DH.
Results: everything stays dry and nice-smelling. Normally, when you pick up something which is cold, then any dampness makes it FEEL cold and damp. We do not have that, all our cold stuff feels cold and dry and instantly warms up under our touch (try it yourself on your boat!). We used to get light mildew up in the hatches, where the relatively warmer air (heated by the seawater) condensed out on the hatch-glazing. We also used to get condensation all year round under berth cushions, after a good night's sleep, always had dampness under cush. We have neither of these symptoms anymore (even in season, never dampness under berths).
Max/Min never goes below zero, even though only 500W greenhouse heater (which means the DH could be a cheaper version, see above). I think this suggests that I am not exchanging my internal air much with the outside.
Finally... we reach September with some water in the bilges, below strum box pick up. By the end of October, mid November, our bilges are dry, although the bottom of the bilge is nearly 6ft below the DH.
I am not good on theories, but maybe the seawater heats the air, relatively, and causes a natural convection - maybe it is the blower in the DH? I don't know, but I have told you the way it is, not the way I think it might be.
I note what someone posted about ventilation - on our 23ft Sonata we used to rely on ventilation - standing all our berth cushions on one edge when leaving, to allow clear air flow... NEVER ENOUGH!!! The cold damp air of the Medway would come in and set up a high Rh, and each spring we had smelly everything. I think this was amplified by the fact that the moisture brought into the boat during the sailing season was soaked up by all the boat's fabric and never really dried before the winter (maybe, I don't know, just another untried theory!!).
A point about quantity of water extracted.. before we discovered about the tilt needed to prioritise the external drain, we left the machine unattended for a fortnight or three weeks, and when we came back, the machine had filled its tank and switched off. I think the tank must hold 2 litres (but that is a guess, I can't remember).
I have no experience of the dehumidifier crystals, but they certainly sound much cheaper than a DH machine, if they work for you.
