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Old 05-05-2021, 06:46 AM   #1
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AC vs portable dehumidifier when leaving boat in Southern Florida

Hi All,



We use our boat intermittently here in southern Florida and return home to Connecticut when not in use for one to up to three months, especially in the heat of the Florida summer. I and the previous owner have always left the ac on at a higher set point, perhaps 75-77 degrees, and hired a caretaker to check on the boat and clean the strainers on a regular basis. Our thinking is that not only are we protecting from mold but also from oppressive cabin heats that may develop here in southern Florida. The only issues we have had are a bit more maintenance on the ac systems. Electricity is included in our dockage lease so finances are not impacted either way. Our AC unit, like most has the capacity for a dehumidifier setting, but I am talking about purchasing a free standing unit which I could store in our dock box when in town.



One of my dock mates pointed out to me that when he leaves, he closes all stopcocks and shuts down the AC unit in favor of a portable Dehumidifier which he runs into the bilge. On Gratitude, I could do the same and run the unit into the sink. His thinking is that failure of a hose on the AC system, or any of the other systems, for that matter could lead to sinking of the boat in the slip if not caught early and a biweekly check would not be sufficient to prevent this. My concern with this is that with extreme southern Florida Heat, am I exposing my boat to other risks even though I would be controlling the humidity?



I'd appreciate any thoughts on this as I will be heading North in a few days for a few months.



Gary LaChance

“Gratitude”

American Tug 435
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Old 05-05-2021, 06:54 AM   #2
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Good question and legitimate concern. We are in the Panhandle of Florida, Pensacola, where humidity can be a challenge. We have a freestanding Dehumidifier that has a setting on it that allows you to set the “acceptable level” you desire, 50% for us. The discharge hose exits in the salon sink and works well for us. Additional we run a fan in the aft cabin. We have been happy with the results.

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Old 05-05-2021, 08:06 AM   #3
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I keep a portable dehumidifier that empties into the sink. The "big" thing is to get the humidity down, not necessarily the temp.



However, it would be very unlikely that the AC unit or the hoses to it would fail if it was properly inspected and marginal hoses replace with new when worn. And if the AC unit just failed, it would most likely shut down and just sit there.... I see little risk, so that is another option. For "me", I'm paying for the power to run it and I don't seen the benefit for AC unless I'll be onboard.


I've used dehumidifiers for several years and even a small one makes a big difference. One can also use many of the passive devices to collect water, which work, too, but a PITA and expensive.


The main thing about the portable dehumidified is that it clunky and big and a PITA to get off the boat for a trip.
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Old 05-05-2021, 08:14 AM   #4
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What size dehumidifiers are you guys running (I know to adjust for boat size...but I want to compare real results to advertised).
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Old 05-05-2021, 08:28 AM   #5
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Quote:
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...One can also use many of the passive devices to collect water, which work, too, but a PITA and expensive.
.....
I assume you mean some sort of desicant system.... Does that really work in a boat?...I can't imagine....

When I first got into playing in the RV world, I bought a pupup tent camper trailer. When stored in the yard and closed up I though it might be a good idea to use a desicant...put in some of those damp rid tubs....
In no time they would fill with water.... I soon realized that it was akin to trying to drain the ocean by siphoning with a garden hose.... Everyday, the day to night thermal cycles would draw in more humidity...it's just a loosing battle....and that's not a boat sitting in water. I've not even tried it in my motorhome.

To the OP's concerns...if heat is a concern, one solution is to shade windows using reflectix... I did this in my RV and while it still gets warm in there it's noticeably better. I found that pillows stuffed in the roof vents do a great job of both insulating and shading those...maybe could do something similar for any hatches. Lately though, since the storage lot has become a mud hole with the rain, I've had more issue with mold & I've wondered if the darkness played a roll...so I've gone back to just using the blinds and shades in most windows, rather than the reflectix.... I'm not sure if it makes a difference or not...
but if I could run an electric dehumidifier I'd most likely block off all the windows....
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Old 05-05-2021, 08:39 AM   #6
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It's a different climate in the PNW for sure, but humidity is a serious problem in the winter leading to Mildew/Mold etc. For the last few years we have used a domestic portable dehumidifier draining to the Galley Sink. It was previously on a 50' boat and it has no problem keeping our new larger boat's humidity down to our setting (40%). It turns itself off when it achieves the set level of humidity, so is fairly economic on electrical usage.
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Old 05-05-2021, 09:05 AM   #7
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Quote:
Originally Posted by psneeld View Post
What size dehumidifiers are you guys running (I know to adjust for boat size...but I want to compare real results to advertised).

I use two of these, one in the galley sink and one in the head sink. I wedge the door to the head open for circulation. I do not run the AC when we are not on board.


Boat is 40' Mainship in Stuart, FL.



It works pretty well, not perfect, but I get very little mold or mildew.


Here is the link.


https://www.amazon.com/Pro-Breeze-El...223320&sr=8-14
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Old 05-05-2021, 09:06 AM   #8
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Small dehumidifiers cost very little, especially in comparison to an AC compressor or even a water pump. However, it is another piece of equipment to be in the way while you use the boat. You could always leave it at the dock.

pete
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Old 05-05-2021, 09:19 AM   #9
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Quote:
Originally Posted by Pete Meisinger View Post
Small dehumidifiers cost very little, especially in comparison to an AC compressor or even a water pump. However, it is another piece of equipment to be in the way while you use the boat. You could always leave it at the dock.

pete

Agreed, we take ours off and put them in the dock box when we leave on a trip of any length.
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Old 05-05-2021, 09:21 AM   #10
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Quote:
Originally Posted by Pete Meisinger View Post
Small dehumidifiers cost very little, especially in comparison to an AC compressor or even a water pump. However, it is another piece of equipment to be in the way while you use the boat. You could always leave it at the dock.

pete
Agree, ours comes off the boat in Spring (took it off 3 weeks ago) and since it is not needed in the summer it is in the attic till November along with half a dozen pancake heaters that we put in the cupboards below all plumbing lines.
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Old 05-05-2021, 09:22 AM   #11
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If you are concerned with a hose or something failing on your A/C then a dedicated dehumidifier that dumps into the sink, not the bilge is a good solution. But don't use one of the cheap, Peltier effect dehumidifiers. They can hardly dehumidify a closet much less a boat. Get a compressor based dehumidifier. You might want to leave a couple of fans on as well to circulate air.

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Old 05-05-2021, 09:24 AM   #12
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Quote:
Originally Posted by Dougcole View Post
I use two of these, one in the galley sink and one in the head sink. I wedge the door to the head open for circulation. I do not run the AC when we are not on board.


Boat is 40' Mainship in Stuart, FL.



It works pretty well, not perfect, but I get very little mold or mildew.


Here is the link.


https://www.amazon.com/Pro-Breeze-El...223320&sr=8-14





Thank you..... do you make a drain hole, leave the tank out?????
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Old 05-05-2021, 11:09 AM   #13
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I drilled a drain hole in the bottom corner and just set the units in the sink. Both of our sinks drain directly overboard and not into the sump, so it's a good solution on our boat. I think (not sure) that they have an auto off switch that activates if the tank is removed.


The little things make a surprising amount of water.
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Old 05-05-2021, 11:25 AM   #14
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I just bought two of these guys:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Rated for 450sqft/25oz per day under ideal conditions. I'm pleased so far but haven't experienced a SW Florida summer with them yet. Drain hose and plugged drain port included. When not in use, they either stow away next to the blender or move to the dock box.

I used to run a portable 12,000BTU a/c unit that drained into the shower when I was based in Ft. Lauderdale. It' worked well but was a royal pain.

As for heat in the boat while I was away, any temp sensitive chemicals or small equipment lived in the fridge. Things like rubber coated binoculars, hand compass or monofilament line seemed to last longer that way.
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Old 05-05-2021, 12:49 PM   #15
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I would go with the dehumidifier draining into the sink. Then either have a couple of fans to circulate the air or leave the A/C on fan only. But that may wear out the A/C blower much sooner and a couple of fans are easier to replace if they wear out.
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Old 05-10-2021, 01:02 PM   #16
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I purchased a boat from Florida. The owner told me the AC had been replaced. He stated he left it on a Dehumidify setting. The unit froze into a block of ice and had to be replaced. Sees a bit extreme but that was his story. I use the small non compress units and they work well.
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Old 05-10-2021, 01:29 PM   #17
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Just add a couple notes: Having the dehumidify selection on the control doesn't mean the option is installed in the unit. Portable dehumidifiers work great and are very efficient - AC with DH is re-warming with an electric heater while the dehumidifier is recycling heat. If you're using the AC, definitely right to keep the temp up in the 70s - cranked up AC is bad, air coming out is wet, nearly saturated, until it re-warms.

Makers of the dehumidifiers should offer advice on how much space they effectively cover. A closed up boat without human activity won't need a whole lot of capacity to maintain so if you go by that it should be ample.

AC set at 80 ish and a DH, everything should be happy.
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Old 05-10-2021, 01:59 PM   #18
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I used a Peltier effect dehumidifier similar to what Dougcole suggested. I drilled a small hole in the tank, pushed some aquarium air hose in it, and drained it to the sink. Before I installed the hose it would fill the tank in a day.

I also bought a cheap hygrometer to see if it was working. It dropped the humidity from mid eighties to low sixties, right where you want it. That solved a big mildew problem.

Possum had a pretty small cabin, V-berth and galley. You would probably need more Peltier dehumidifiers or one of the bigger compressor ones.

Buy a hygrometer so you can see what it is doing. You want to shoot for 60% or less.
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Old 05-10-2021, 02:08 PM   #19
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My permanent residence is S. Florida, so the boat is here during the winter months, about 6 months, mostly just storage with occasional weekend trips (live aboard at the rental dock is not allowed). But even in the winter months, it gets hot and humid.

I've been using multiple containers of "Damp Rid" and a fan in each room in the boat to control the humidity, and it works well. They get emptied and new crystals about every 3-4 weeks. No electricity, no danger of systems failing or a thru hole fitting failing (at least not because of the dehumidifying efforts). If you have someone looking after the boat, this is also the easiest thing for them to handle. One word of warning: the liquid produced by the crystals is a very salty brine. Spill it on the rug, and the Admiral will have you scrubbing carpet. This I know from experience.

I've been a boat owner for over 40 years, and Damp Rid has always been my storage savior. Not once have I had a mold or mildew problem.

Granted, it's old technology, but sometimes the old stuff is the best stuff.
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Old 05-10-2021, 04:55 PM   #20
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south fla heat

Have had boats in south Florida for 40 years. If leaving for any length of time would use a dehumdifier draining into sink . Would shut all seacocks and vacumun bilge dry. You want the boat to heat up to put the moisture in the air ,so that the dehumdifier can dry it out to a % of moisture in the air. not temp, Running the A/C will only run until temp is reached ,so it could be 75*- 80* still with 80% humidity. Use a dehumdifier to dry the boat out,with small fans to move the air around the boat. Open lockers and drawers and space clothing for circulation . Might try charcoal in small tins to asborb odors, and a open gallon of bleach in each head to help stop any mildew .
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