The problem with condensation...

If you are a dehumidifier, condensation is not just good, it is your raison d'être.

But if you are a fuel tank, condensation is bad... no, it is evil.  Here's what happens:

1. The sun goes down.
2. The tank cools off.
3. Because it is cooling, the air inside contracts, wanting to pull a vacuum
4. But you have a vent on the tank (thank goodness!), so damp night air flows in thru the vent.
5. And the moisture in the damp air condenses on the tank walls and the surface of the fuel itself.
6. Eventually, the moisture makes it to the bottom of the tank.
7. The sun comes up
8. The tank heats up.
9. The air in the tank heats up, and grows in size.
10. The air exhausts thru the vent line, leaving the water in the bottom of the tank - after all, it is covered by a thick layer of diesel - it is effectively out of circulation.
11. Lather, rinse, repeat.

So a layer of water slowly accumulates in the bottom of the tank.  Aside from the things that this can do if it reaches your engine, the water will eventually host a collection of microbial life - life that lives in the water but eats the diesel as food.  The end result of this microbial life is that the water becomes acid.  And that, my friend is a problem.  No one wants acid in the bottom of their tanks.  Most especially if they are aluminum.

So how can you prevent it? 

My friend Drew over at Sail Delmarva, who does this professionally for large industrial tank farms recommends this product from H2Out Systems:

This is a flow-thru container made of diesel-compatible materials, and filled with silica gel.  You know, the same stuff found in those little "Do not eat" packets in there with your new digital camera or your vitamins (have you ever been tempted to eat one?). 

This device gets installed in your fuel tank vent line.  When there, the silica gel adsorbs the water from the incoming air; only dry air gets to the tank.  The silica gel is treated with cobalt chloride which serves as a moisture indicator.  When it turns from blue to pink, it is time to regenerate the silica gel. Regeneration consists only of heating the silica gel in a low temperature oven for a few minutes.

According to Drew, there is some self-regeneration, depending on the size of the filter and the size of the free airspace in the tank.  When the dry air in the tank expands on heating, it passes thru the filter in the outbound direction, and strips moisture out of the filter.

Pretty simple, eh?  But there is one important caveat:  the moisture filter must be protected from contact with diesel - either by design of the installation or by process constraints.  If diesel gets into the media, it is ruined.

So I have this one installed - I'll let you know how it works in about 6 months.

The problem with condensation...

Painting vs. cleaning

It's a question that must be asked: Is it better to clean? Or is it better to paint? Or both?

When the subject is a compartment that has mildew deeply embedded in a rough fiberglass surface, the answer is clear, and empirically proven:  Paint.

The compartment above is against the hull.  That is, the back wall in there is actually the hull itself.  In the winter, that hull surface is nearly the outside air temperature - because the compartment is full of Jane's clothes (in Tupperware boxes and plastic bags), so there is little air circulation.  But the moisture finds its way to the hull and condenses there.  Consequence:  mildew.

For you purists out there, I first tried cleaning the surfaces with bleach and water.  It worked, sort of, but was slow and messy.  And it was clear that when I was done, another coat of paint was still going to be needed anyway.

So I just got out the Brightsides - I love this stuff!  A single coat completely covered the mildew.  And surely killed it.  I wore an organic vapor respirator while I applied it, by necessity - I won't be sleeping in the aft cabin tonite!  The paint fills in the surface roughness that the mildew loves to hide in, leaving a beautiful, smooth, shiny surface.

And since the aft cabin is off limits for a while, I'm going to also sand and re-varnish the sole in both the aft cabin and the aft head after lunch.  But that's another story.

Painting vs. cleaning

Tiny heat pump, with benefits

I've blathered on about our heat pump enough that by now all of you should know how they work:  They use electrical energy to move heat.  Of course, this means that there has to be a heat source.  Eolian's heat pump extracts heat from sea water.  And household heat pumps typically extract heat from the outside air.

But here's a heat source you may not have thought of:  condensing water.  A dehumidifier removes moisture from the air by condensing it.  Annnnd... condensing water releases  970 BTU/lb, 1010 BTU/pint.  So is that a lot of heat?

Dehumidifier capacity is typically rated in pints/day.  Ours is a small one, rated at 25 pints/day, or a little better than 1 pint/hr.  Using the numbers above, our little heat pump will deliver 1052 BTU/hr.  It does that while drawing 1.6 amps - that energy (about 600 BTU/hr) also gets delivered into the boat.

So let me put all that into clear perspective for you:

Our little tiny dehumidifier, which draws only 1.6 amps, is the equivalent of an 484 watt electric space heater.

We keep the dehumidifier in the head; this explains why it gets so warm in there when we take a shower.

Of course, these numbers assume that the dehumidifier is working at capacity, and that only happens when the air is very humid, like it is in the head when someone is showering.  At other times, the heat output will be less.  But like all heat pumps, the efficiency will never fall below 100%.

So think of that dehumifier as a tiny heat pump with these side benefits:

• It keeps the boat interior dry
• It provides an apparently never-ending onboard source of distilled water

I consider ours to be one of the best $125 we've ever spent.

Tiny heat pump, with benefits

Boat ovens

Jane recalled that the first time we rented a boat that had an oven, it was an unbelievable luxury.  Our kids were little, and we had chartered a Catalina 30 in the San Juan Islands.  When the weather turned cold, Jane baked cookies in the oven.  Not only was it great entertainment for the kids, it heated the cabin.  But it touched something more primitive in me - a deep "comfort" thing.

Boat ovens are small (I'm speaking of sailboats here).  There is no way you are going to roast a turkey in there, even a small one.  A turkey breast perhaps, or a chicken would fit.  And in fact, most normal bakeware is too big - you have to shop for "mini" versions of cookie sheets, etc.

Boat ovens are gas ovens- a wonderful thing for someone who has had nothing but electric ovens with their high radiant heat loads (burnt on the bottom, raw on top) for decades.  And they do heat the cabin.  This is a boon in the winter, but it keeps us from doing much with the oven in the summer (we do a *lot* of grilling in the summer).  Also, burning that propane and dumping the moisture it produces into the cabin was a problem before we got our dehumidifier.  You *will* want to have a dehumidifier if you're planning to use an oven when the cabin is sealed up.

You probably don't think about it, but the stove and oven in your house are *level*.  Because of this, your cakes unthinkingly rise evenly across the pan.  But boat stoves are gimbaled.  Because sailboats heel, the stoves are made to  swivel so that the oven is on an even keel even when the boat is not.  This would seem to be a blessing, but it is a mixed one.  Depending on what is in the oven and on top of the stove, "level" is a relative term.  We keep a small bubble level handy nearby so that we can level the stove using the tea pot, etc when the gimble is unlocked.  And don't you dare open the oven door when the stove is unlocked and free to pivot, because it will tilt uncontrollably, and spill it's hot contents all over you.  Most of the time, we keep the stove/oven locked into place when we are at the dock or at anchor.  But when baking that cake, I'll free it and apply weights to level it to get as even a result as I can.  The stove is gimbaled in only one plane: to account for the boat heeling.  Variations in the fore/aft plane cannot be corrected, other than by moving prodigious quantities of "things" from the aft cabin to the forward cabin, or vice versa.  So of course, we don't do that.

There are several marine stoves manufactured out there.  Ours is a Seaward Princess.  Perhaps its main competitor is the more expensive Force 10.  In a major refit, a boat that was near us at the dock upgraded their stove - they chose the Force 10 because, "if it's more expensive, it must be better."  It turned out that this is one of the times that the old adage was *not* true.  Not only is the Force 10 more expensive, but its oven volume is about half of that in the Princess.  Further, the oven is equipped with a totally inadequate burner.  It took forever to heat up, and never would reach 400 °F.  They eventually pulled it out and replaced it with a Princess.  YMMV of course.

Jane just reminded me of another oven incident - we were anchored off of Hope Island, riding out a storm.  I baked cornbread - it heated the cabin, made us feel cozy, quelling the storm anxiety, and as a bonus it tasted good too!  Cornbread is for me a comfort food.  Baking cornbread somehow feeds my soul.

It may be small, but our little oven bakes up a lot of comfort for me.

Boat ovens

Public safety item

I found this on the Voyages of Sea Trek blog.  As it is a safety item, and in fact one which could affect some of those on our dock, I feel it is important to get the word out as widely as possible.  I'm sure Chuck and Susan would agree.  Here is their posting:

Dehumidifier Recall

We try and post any safety issues we find that would have a affect a broad number of boaters and we feel this is an important one since many of us in all climates along the eastern seaboard especially, could be affected. We use a dehumidifier all of the time on board Beach House but not any of the ones affected by the recall. Nothing is more frightening and devastating for boat owner like a fire so we considered this one important. This humidifiers can be purchased on line or at many home improvement stores. Check the link and be sure yours is not included

The U.S. Consumer Product Safety Commission has issued a recall of 98,000 dehumidifiers sold under the Goldstar and Comfort-Aire brands between January 2007 and June 2008. The model in question, manufactured by China's LG Electronics Tianjin Appliance Co., has a 30-pint resevoir with a front-loading bucket, and a red shut-off button. This unit has been determined to be the cause of a number of fires — and we all know how boat fires usually turn out. To see if your dehumidifier is on the recall list, check this site.

Please check to see if your dehumidifier is on the recall list. Boat fires never end well.

Public safety item

Why didn't we...

I don't know why we didn't. You would think that we would have long ago.

Living aboard and dealing with the problems of humidity, especially in the winter when the boat is sealed up should have pointed us at this solution sooner.

In a dock gathering discussion last week, we realized that most of the other boats were keeping dehumidifiers running in the winter.

But my memories were of the huge clanking monster of a dehumidifier that my parents ran in the basement of our childhood home. It was a heavy, file cabinet-sized unit that needed its own circuit - it drew 15 amps. Not exactly appropriate for a boat.

But now we have the world's products at our fingertips - I did a quick Internet search and found this one - it draws only 1.6 amps, is small enough to live in the aft head, and yet is capable of pulling 25 pints of water/day out of the atmosphere inside the boat. It even has provision for a continuous drain (which I haven't set up yet), that would go right into the shower sump it is sitting above. Oh yeah... and that is distilled water it is producing too - ideal for the batteries. Finally, condensing water produces heat, so it functions as a small space heater too (you can almost think of it as a tiny heat pump).

One of the dangers of living with problems is that they cease to be viewed as problems after living with them long enough. If it hadn't been for that casual dock conversation, we'd still be living with the humidity.

Why didn't we...