Greenhoue tube heater or dehumidifier ?

[Badger]

I am keeping the boat in the water this winter but want to keep her dry down below. The galley sink is a pump out affair, so any water draining into it will build up. Is there any soultion to this or should I just put a tubular greenhouse type heater on board ? What set up works best ? Thanks.

 

[Ex-SolentBoy]

I am keeping the boat in the water this winter but want to keep her dry down below. The galley sink is a pump out affair, so any water draining into it will build up. Is there any soultion to this or should I just put a tubular greenhouse type heater on board ? What set up works best ? Thanks.

There have been several threads on this recently, so some searching will give you a lot of input.

My view is this, and do them in order.

1. Make sure the boat is well ventilated.
2. If you can, heat it. Tubes are fine, but if the boat is of a reasonable size then a greenhouse heater like a Dimplex 500 is much better.
3. If you want to spend even more money then dehumidify as well.

 

[Touchwood]

Hi,

I don't have any specific experience with keeping boats dry, but I am a ventilation engineeer and I know about the physics - and I really don't think heating is the answer.

The problem with dampness isn't the moisture in the air, it's when that moisture condenses out on a cold surface. If you heat the air inside the boat, with a ready source of moisture available the air will just take up more moisture. As soon as the air is cooled (by contact with a cold surface) the moisture condenses out.

De-humidification also I doubt is the answer. Good ventilation is usually the best way to combat humidity problems.

Interesting to see if any of the experienced boat owners out there agree with me - I have been known to be wrong!

 

[Leighb]

There have been several threads on this recently, so some searching will give you a lot of input.

My view is this, and do them in order.

1. Make sure the boat is well ventilated.
2. If you can, heat it. Tubes are fine, but if the boat is of a reasonable size then a greenhouse heater like a Dimplex 500 is much better.
3. If you want to spend even more money then dehumidify as well.

I agree that ventilation is the key if you are not using a dehumidifier, but surely if you do use one you need to close all air vents otherwise you are trying to dehumidify the whole of the UK

I have been using a dehumidifier alone the past 2 winters, and everything has stayed nice and dry with all vents shut. The only problem was that it stops working when it is too cold and so I am adding a low wattage tube heater this year.

 

[VicS]

Basically the physics says that condensation will occur on any surface which is colder than the dewpoint.

Therefore

Prevent surfaces becoming that cold by heating.

lower the dewpoint by dehumidification.

prevent moisture build up and consequent raising of the dewpoint by ventilation.

Over ventillation combined with heat will mean you are trying to heat the planet or with dehumidification will mean you are trying to dry out the whole planet so delicate balance between all three is the ideal.

 

[Touchwood]

Basically the physics says that condensation will occur on any surface which is colder than the dewpoint.

Therefore

Prevent surfaces becoming that cold by heating.

lower the dewpoint by dehumidification.

prevent moisture build up and consequent raising of the dewpoint by ventilation.

Over ventillation combined with heat will mean you are trying to heat the planet or with dehumidification will mean you are trying to dry out the whole planet so delicate balance between all three is the ideal.

You are quite correct VicS; however, putting a heater in will heat the air inside the boat but have little effect on the surfaces likely to attract condensation IMO.

 

[Quandary]

Keeping boats afloat or ashore over the years in the colder wetter fringes of the U.K. I am with the faction who advocate through ventilation and then more ventilation. For instance I have made up a louvred winter hatchboard which is about 40% slots. The boat has intake vents over the forward cabin and dorades over the main cabin with solar extracts aft. Cabin doors, lockers etc are all open as much as possible and any cushions etc. which are not removed are stacked on edge. Cockpit lockers which have been emptied have the lids propped up a couple of inches.
I still have a heater and a dehumidifier but with so much free air movement either heating or dehumidifying Scotland would not be worth attempting so I don't use either now.

 

[Badger]

Any ideas on how I can overcome the problem of only having a small pump out sink in the galley for the dehumidifier to drain into ? Where or into what else could I drain off the water ? Any ideas ?

 

[SailBobSquarePants]

Ventilation not always that easy...

From what I have seen on friend's boats, ventilation on some modern boats isn't that easy. Modern boats have sealed, flush, lexan hatches that are difficult to leave slightly open without water/rain ingress (and a security risk), and many of them lack big dorades. A friend's 50' Jeanneau (with that sort of arrangement) was a breeding ground for mildew last year, despite having ventilated washboards and trying to ventilate as much as possible. If your boat is of that order, a de-humidifier may almost be a requirement.

Older boats, especially those designed without opening side hatches and few roof hatches, may have a greater number of passive ventilating dorades, etc., that can provide better ventilation. It may be necessary to create ventilated washboards however.

I used a dehumidifier last year, and had absolutely no problem with any mildew, condensation, etc. I consider the £120 I spent on it perhaps the best money I spent on my boat. If your sink does not drain, you may be able to plumb it out via a hole in a washboard into the cockpit perhaps, or into a bilge fitted with an automatic electric pump?

 

[johnalison]

I have used a dehumidifier for the last 10 years. Although it is possible to ventilate a boat, to do it well means providing a cover over the whole boat and leaving hatches open. This is not practical when leaving the boat rigged and so dehumidifying is much simpler. In sunny Essex the temperature seldom drops low enough for me to want a heater and with the boat in the water I don't usually need to drain the fresh water system.

As I put my dehumidifier on a timer to run at night I harbour the fantasy that the machine will be producing enough waste heat to raise the boat's temperature slightly anyway. In any case, the boat remains dry and we usually leave our bedding out ready for occasional use and this always stays fresh and crisp-dry.

 

[Quandary]

Any ideas on how I can overcome the problem of only having a small pump out sink in the galley for the dehumidifier to drain into ? Where or into what else could I drain off the water ? Any ideas ?

Surely if you have the boat sealed up tight enough for a dehumidifier to be effective, a 20litre water container will hold at least several weeks output.

 

[davidej]

Our boat came with a smart (but very heavy) tailored tarpaulin.

We winter ashore and I have never fitted this on the grounds that a bit of bird s**t is better than the loss of ventilation.

Do the experts think I am right?

 

[Quandary]

Having a teak deck and cockpit (not my choice, but I could not have the boat I wanted without them) I had covers made from the first winter. ( you can get really precious when you spend a lot of your money) They fit over a ridge board and are open at the pulpit and pushpit and allow plenty of air through, they also facilitate leaving hatches open and leaving a nice big vent hole where the mast come through the deck. They are in two pieces to allow fitting around the mast and over the boom if wintered afloat but so far the boat has been lifted every winter. However in winter 2008 the big Christmas storm bent two stanchions, so since then I take them off and bring it down over the toerail.

 

[nimbusgb]

Our server room dehumidifier uses one of these maxi orange to pump out the condensate waste. Effectively an overpriced bilge pump.

I'd be tempted to get a car windscreen washer bottle and pump from a breakers yard and put some sort of float switch or even a timer in ( say a 5 minute run every 24 hours ) it and a piece of plastic hose out of a vent somewhere.

 

[fisherZ]

Any ideas on how I can overcome the problem of only having a small pump out sink in the galley for the dehumidifier to drain into ? Where or into what else could I drain off the water ? Any ideas ?

Use a beer/wine fermenting bin, with a close fitting lid.

 

[lw395]

Dehumidifiers can work wonders, especially if you are sailing the boat through the winter, it will dry out any oilies, sails or whatever you leave below. Very handy on a race boat where you have a wet kite to deal with.
Ventillation might be a better answer if you are around to open up the boat on dry days and shut it down on damp days. The humidity in Portsmouth is often quite high, temperature does not have to drop much at night to get lots of dew. I expect most watery places are similar! I think you might need a powerful heater to beat this?

In either case, it helps a lot if you can eliminate even the smallest of rainwater and bilge leaks.

If your sink does not drain, you could put the dehumidifier high up and plumb the drain out through the washboard or any other hole that's convenient.
Alternatively, a 25 litre plastic can will keep it going for a long time unless you have a serious damp issue! It should be a closed container to stop the water evaporating.

 

[Badger]

Brilliant idea ! I have founda 20 litre one with a small grommet on the lid that I could poke the hose through. Thanks !

 

[oldfatgit]

Any ideas on how I can overcome the problem of only having a small pump out sink in the galley for the dehumidifier to drain into ? Where or into what else could I drain off the water ? Any ideas ?

If using a de-humidifier, connect the tube output to a large plastic container via a sealed connection and have it lower than the unit. It will fill and if the water keeps coming, back fill into the unit tank to eventually actuate the cut off.

We use a combination of small oil filled radiator set on frost guard and a dehumidifier on a time switch. Seems to work very well with the dehumidifier working from noon to 6 pm.

 

[Saguday]

Keeping boats afloat or ashore over the years in the colder wetter fringes of the U.K. I am with the faction who advocate through ventilation and then more ventilation. For instance I have made up a louvred winter hatchboard which is about 40% slots. The boat has intake vents over the forward cabin and dorades over the main cabin with solar extracts aft. Cabin doors, lockers etc are all open as much as possible and any cushions etc. which are not removed are stacked on edge. Cockpit lockers which have been emptied have the lids propped up a couple of inches.
I still have a heater and a dehumidifier but with so much free air movement either heating or dehumidifying Scotland would not be worth attempting so I don't use either now.

My experience is similar to this. We laid up Kioni for a very extended period when we worked overseas - turned out to be five years in the end - and it was impractical to put heaters and humidifiers in for this length of time. We covered her with a canvas cover and I wedged up the forehatch slightly to get some air in. Followed all the usual guidelines about mattresses on edge and cupboard doors left open etc. Frankly I was dreading it when I climbed aboard last year for the first time but I was astonished to find there was not a spot of mildew anywhere - no evidence of damp or funny smells at all.

On Saguday which is a much newer boat we have dorade vents and our hatches all have a lockable, slightly-open position for ventilation (these are standard Lewmar hatches so don't know why this shouldn't be the case for most modern boats). I'll be repeating the experiment this coming winter with her so will see how it goes.

 

[richardbrennan]

Dear Badger

The internal tanks on dehumidifiers vary greatly in their capacity. If you get one with a large enough tank and can get to the boat fairly regularly, then you can just use this and not bother with an overboard drain. I am also of the faction that you need heating as well as the dehumidifiers don't like cold temperatures; try and get one with a hot gas defrost to de-ice the thing.