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Discussion Starter #1 (Edited)
Back in 1992, I fitted a 3 kW Eberspacher forced air diesel heater. It has been reliable.

A long time, somebody warned me that although they will heat the boat, they will not dry the boat. They are right, and I have grown tired of it. You arrive with the boat damp, you start the heater, and 12 hours later you leave with the boat warm and damp, with condensaton just about everywhere. I have tried opening the hatches a wee bit to gain some air circulation, but it made little difference, and there is no point in opening all the hatches as the heat leaks out. I guess the problem is that the Eberspacher just re-cycles the boat's air, and does not draw in "new" air to aid the boat to dry.

So here comes the question. I have been on board a few ships that used a solid fuel heater, using charcoal. They certainly dry the boat, and very quickly. But, will a diesel heater operating on the same idea do the same job, namely, will it dry the boat? I dare not burn wood in a solid fuel heater, as there will be smoke a-plenty and I am not into that. I could go the charcoal route, perhaps even the diesel route with one of these, for example...

Newport Diesel Heater for boats.* Manufacturer: Dickinson Marine

.... but I have got to be sure it will dry the boat before I begin that installation.

This looks like another good one....

Welcome to SigMarine.com - Products - SIG-100


I have not got a great deal of space, but there is one place on the ship where it could go, as long as it will be effective when it does. It really must assist in drying the boat.

Thanks.


Rockter.
 

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Rockter,

That would probably be a pretty good solution, if diesel is what you want. I couldn't tell whether the combustion chamber on that unit is sealed from the boat, or whether it draws air for combustion from the interior of the boat?

We use something similar to what you linked, but ours is Dickinson's propane version of the Newport. What I like about ours is that we can see the flame (ambiance), yet the combustion chamber is sealed from the boat interior. Air for combustion is drawn in from outside the boat via a double-walled chimney. This also has the beneficial effect of insulating/cooling the chimney stack (exhaust is the interior portion), so it does not get quite so hot within the boat.

If you have propane aboard, it is a very clean fuel and is relatively easy to install. These heaters are very dry, because the exhaust from propane combustion does not enter the cabin at all. A little built-in fan helps to circulate the heat better, as do your regular cabin fans.

But I do not know if it will be better than what you have...


Not the best photo, but you can see ours here. We like it a lot:

 

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the pointy end is the bow
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I've heard the same thing that John mentioned, is that the solid fuel type stoves, draw warmed moist air from inside the boat and send it up the chimney. We have the Dickinson Antartic stove and it seems to dry out the boat, although it doesn't heat it up very fast.

 

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Discussion Starter #4
Guys :

Thanks.

If it doesn't draw cabin air for combustion, then it will, I fear, be little better than the Eberspacher, which has itself, a separate combustion cycle. The exhaust for the Ebespacher is also separate, and does not enter the cabin.

I think the heater must draw on cabin air, or there is no through-put up the chimney, and that boat is not going to dry. With the Eberspacher running, condensation is dripping everywhere, not because the heater is adding water vapour from the combustion, but because the heater simply heats it up and it hits the colder walls.

Given 12 hours of that, the walls and portlights are soaked. It was -5 degC outside, and about +16 degC inside, but still the condensation persisted, and steadily worsened.

Does anyone have a heater that draws on the cabin air? Does it dry the boat? I don't mean just heats the boat, but dries it?
 

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Rockter,

Drawing air for combustion from the exterior of the boat has always been a desirable feature from my perspective. In fact, the units that don't do this usually are equipped with an oxygen depletion sensor, which to my mind is worrisome.

I do wonder a bit about your scenario. If the ambient air is damp, and the heater unit draws air from within the cabin for combustion, isn't that air going to need to be replaced by more damp ambient air, from outside the cabin? In which case, you will always need to keep a hatch cracked, which in turn will mean a cold draft, which in turn means less efficient heating, and more of the damp ambient air circulating through in the cabin.

Our heater seems to dry the cabin, anyway. Maybe all it's doing is warming the air enough that it can hold more evaporated moisture? But our problem with condensation in cold weather has definitely diminished since we installed the heater.
 

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the pointy end is the bow
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I do wonder a bit about your scenario. If the ambient air is damp, and the heater unit draws air from within the cabin for combustion, isn't that air going to need to be replaced by more damp ambient air, from outside the cabin?
The colder air outside is supposed to be drier humidity wise than the warm air inside, because cold air holds less moister than warm air. At least that's the way it was explained to me. The Dickinson website actually promotes their heaters as giving off dry heat.

DickinsonMarine.com - Diesel Natural Draft Heaters
 

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Discussion Starter #7 (Edited)
erps :

I think what they mean by "dry heat" is that they are not adding water to the cabin air from the combustion. The cooker, for example, creates condensation readily as burning the gas in air produces water vapour a-plenty.

If the Dikenson heater has no cabin air through-put, then all it is doing is what the Eberspacher does and heats the cabin air.

The Taylor heater has a single flue and so must(?) have a cabin air throughput? I think the Dikenson has a single flue as well, so I am encouraged. When the day comes that when I start the heater, and 6 hours later condensation is not dripping down the portlights, then I will be doing beter than at present. I guess I need to find someone with a Taylor or Dickenson heater, or similar.

I know a solid fuel heater will dry a boat... I know someone has one.... but I cannot speak for the diesel heaters with flue, as yet.
 

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I have the Dickson Newport Deisel heater and it was installed on my boat when I bought it used. The boat has never really had a mositure issue from the start but I can def say that when ever I light the Dickson, it sure feels like it makes the boat extra dry. I used it a lot in the beginning of the season last year and after it has been on for a few hours, everything in the cabin seemed real dry and warm. So I have no scientific proof but just wanted to comment on my experiences incase it may help.

 

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... The cooker, for example, creates condensation readily as burning the gas in air produces water vapour a-plenty.
Rockter, yeah, that is likely one of the biggest advantages we are seeing. Before we installed the cabin heater, we used to do a lot of extra cooking/baking/pre-heating to help warm the cabin and we would invariably end up in a rainforest below decks. Solid bronze portlights are especially good condensing surfaces!:)

One of the other variables I seem to remember was that the diesel heaters need a longer flue/chimney for draft purposes. I think that is why we see so many diesel heaters mounted low-down as in erps' and nk's photos. Personally, I like that look, especially when coupled with a tiled- or metal-lined fireplace. But the propane heaters only require about 24" of chimney -- they can often work in tighter spaces. So be sure to measure carefully!
 

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Discussion Starter #10 (Edited)
Guys :

Thanks.

I just have to be sure they are drawing in cabin air for combustion and so creating a through-put. Some of them draw their air for coubustion down a concentric flue arrangement, and so there is no through-put of cabin air.

I wonder does the flue have to be straight, because I think I can get the necessary length by using a dog-leg in the flue.

nk : do you not fry the cushion material next to it there? It looks very close!
 

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I will show ours once again.
Captain Rizzo and Alex monkeying around on a chilly spring evening.
 

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Courtney the Dancer
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I recently installed a Wallas forced air furnace and the folks at Scanmarine in Seattle told me it was very important to have one of the return air ducts open to outside air in order to dry the boat out. I'm not sure how your furnace is set up, but if your return (combustion) duct is not at least partially open to exterior air then maybe that is the problem? Our furnace has two 3" return lines to it from the interior, and one of them has an opening to the outside air, so this line is app. 50/50 inside/outside air. You might give Scan a call, they are very helpful.

Boat heating and cooling experts, Wallas heaters, Ardic heaters and other diesel boat furnaces - Scanmarine.com

John
 

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Rockter:

Talk to your Eberspacher dealer. Most forced air diesel heaters are able to have outside air ducted to them, which is drier and more oxygen rich than your cabin air. A blend of cabin and outside air is what we recommend for Wallas heaters and it should work for your Espar (aka Eberspacher).

Plumbing a mix of makeup air to the heater should help dry your boat. Your problem just sounds like an installation deficiency. Again, talk to the Espar dealer in your area.

Doug McElroy
Scan Marine Equipment
 

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Discussion Starter #15 (Edited)
Westlake :

Good thinking. Thanks.

The Eberspacher is right at the stern of the ship, and it uses a super-hot combustion chamber drawing air through the vertical tube in the picture that exhausts out a wee through-hull. The combustion chamber exchanges heat via an exchanger to a separate cabin air cycle duct of, perhaps, 4" in diameter (the fat one on the left, exiting the heater), and the heat is ducted forward where it exits at 3 points into the cabin.

I have heard before that they don't dry the boat. Mine doesn't. It does warm the ship though, typically about 20 degC higher than the outside temperature (measured just under the cabin top at the sampson post).

I liked the idea of ducting outside air, and I could extend the intake...

WK Union 36 worm-gear steering picture by rockter - Photobucket

...such that it drew in outside air. I might need another through-hull though, and that makes me nervous. As an experiment, I could rig up a bit of tubing to that heater air intake (on the right of the heater) and route the tube out of the lazarette door. I could perhaps pack the open door with rags to attempt to seal the door, simulating a through-hull.

It would not be expensive tubing as it is on the cold side of the duct.

It would be worth a try, methinks, and would cost very little.
.
 

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Rockter

Whether the air is drawn in from outside, or re-circulated round the boat, the moisture content is unlikely to be hugely different. If you imagine (hypothetically, of course) that the boat is completely sealed and your Eberspacher is heating by re-circulating, then the moisture content will remain the same, except in one case it will be suspended in cold air and in the other it will be suspended in hot air. If some of the surfaces (for example, the coachroof) are poorly insulated and cooled by the outside temperature, then the hot air will condense on the cooler surfaces and create moisture. In addition, human beings produce large quantities of moisture (I will resist the temptation to go into gory details here, but breathing, for example, produces lots of moisture) and will be constantly adding to the problem, as will cooking etc.

Of course, the boat is not (or should not!) be completely sealed and there is an interchange of air between the outside and the inside which will vary according to how much ventilation you have.

So, in my experience, the problem is not the heater but a combination of proper ventilation and insulation. Some form of dehumidification might also help.

I speak from experience, by the way. I had a 23' Virgo Voyager in the UK which I sailed on both the East and West Coasts of Scotland. It had an Eberspacher and, even with four people on board, was always OK interms of moisture. Of course, this is the UK we are talking about here, so a certain amount of dampness is inavoidable.....

I would keep your Eberspacher. It is a wonderful device.

Stuart
 

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Courtney the Dancer
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Leither- as I understand it, by introducing outside air it will somewhat pressurize the inside of the boat forcing the moisture laden warm air out and replacing it with drier, cooler air. Similar to opening a window a bit in a car that is fogged up inside. It seems to work, our heater keeps the boat dry.
 

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Leither- as I understand it, by introducing outside air it will somewhat pressurize the inside of the boat forcing the moisture laden warm air out and replacing it with drier, cooler air. Similar to opening a window a bit in a car that is fogged up inside. It seems to work, our heater keeps the boat dry.
Makes sense to me. I guess that was my point abou the importance of proper ventilation.......

Stuart
 

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Discussion Starter #19 (Edited)
If the cabin is very mildly pressurised, and the Eberspacher should do that a wee bit if it draws air from outside, then perhaps it will improve a wee bit. It is not practical, surely, to change the insulation on a ship after it is built?

If I can duct the air in from outside, surely it should be drier? It is not simple to do that though, not without the most awful extra through-hull.

Humidity is never that high in Scotland, outside at least. The condensation appearing on the inside surfaces of the boat must happen because of elevated humidity inside, otherwise it would similarly be condensing on the outside, as it is cooler there (call the argument as still air, with cloud cover). Elevated temperature allows air to hold more moisture, not less, surely?
 

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Rockter

I certainly reckon it is worth a try. With your Eberspacher being near the stern, would it be possible to have an air inlet somewhere on the inside of the cockpit?

In terms of insulation, I was just thinking about uninsulated surfaces. In my Morgan, for example, the inside of the coachroof is lined with hard plastic and, in your climatic circumstances, would produce some devilish condensation. If I was using it in an environment where that would be a problem, then I would need to put up headlining material. In the UK, I remember having to put something between the seat cushions and the interior GF to prevent condensation from the bodies occupying the seats!

Stuart
 
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