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Old 13-08-2017, 18:18   #1
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AC system sizes?

So we wanted to cool the boat quick and easily so that we could work on it for the rest of the season. We went down to the big box store and bought and 8,000 btu portable AC, which I vented through a window. Unfortunately the unit only cooled the boat off to slightly below the spontaneous combustion flashpoint of fiberglass. Even at night, running on high constantly, it only cooled to about 82 degrees.

I have about 70 square feet of floor space including the head. If this 8,000 btu unit isn't even touching it, im concerned that a 16,000btu marine AC unit is still going to struggle.

My boat is a 1967 Chris Craft Commander 31'. What kind of system is recommended for a boat my size, and what kind of costs am I looking at? A friend of mine will help me install it as he just did his.
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Old 13-08-2017, 19:12   #2
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Re: AC system sizes?

Let's look at your boat and do some math...

According to this your boat is 31' in length and 11'9" in beam.
Photobucket

20 feet of your boat is interior space, so, 20x12=240 sq feet. ( Yes, I know this isn't exact, but this is a quick and dirty estimate. )

Next we visit https://learn.compactappliance.com/b...ng-calculator/

By setting it to 3 people, in the sun and with a kitchen, we get 13,400 btu.

Since boats are not insulated very well, 16,000 would be a good match up, you'll be looking at around $1,800 + ducting if you do it yourself. Here's a quick link.
https://www.westmarine.com/buy/webas...8aAs8oEALw_wcB

Hope this helps!
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Old 13-08-2017, 20:39   #3
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Re: AC system sizes?

Most boats are not insulated as well as houses, so it takes more AC. If you want to maintain a specific temperature or specific temperature drop from outside, see a marine AC company. Otherwise buy more cooling than you think you need. That's what I did. My main deck cabin is about 50' and I have an 8,000 and 12,000 vented portables. It stays cool at 90į+. My cabin was built in the 70s w/o insulation and I have been gradually adding that as I replace or redo the wood panels. Insulation makes a big difference. Especially in the winter.
Portable AC comes with either 1 hose or 2. The single hose AC is drawing cool air from inside the cabin to cool the freon. That air is made up from leaks of outside air coming into the cabin. So you're really cooling more air with a single hose system.
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Old 13-08-2017, 20:42   #4
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Re: AC system sizes?

What kind of insulation are you using? My cabin goes right to the hull walls and is lined with Berber carpet. The only place I could probably put insulation is in the ceiling between the glasses in beams.
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Old 13-08-2017, 20:55   #5
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Re: AC system sizes?

Can you get any shade over the boat, helps a bunch. The lack of insulation is an issue, as stated before.
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Old 13-08-2017, 20:58   #6
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Re: AC system sizes?

Not in the slip we're in. It's uncovered. I'm not sure about tenting shade cloths over it either.
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Old 14-08-2017, 17:36   #7
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Re: AC system sizes?

Thanks for the responses. After doing some research last night, I think the 16,000btu will be the size for my boat, but if I can afford it I'm going to go with 24000btu. I'm going to have to do this in steps due to my budget, so I have some questions.

Question 1, my boat has previously had a water cooled system installed, so the through hulls, (and possibly pump, strainer, and wiring) are still in place. If it isn't, are water pumps and strainers proprietary, or can I install those beforehand?

Question 2, do 110v units cool as good as 220v units? If so I'd like to install a 110v unit with a smart start module so that I can run it off of a Honda 3000 carry on generator.

Question 3, since we live in a rather warm climate we really don't need a reverse cycle unit. Are there any units that are AC only?

And lastly Question 4, we have a shop called Boaters Resale shop a few blocks away. They have a LOT of used units. Are there any concerns about buying a used unit, and if so, when inspecting them, what are the things I should look closely at?

Thanks in advance!
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Old 14-08-2017, 17:53   #8
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Re: AC system sizes?

The portable you bought isn't cooling worth a crap because it's drawing hot air in as well as cooling the air. The hose you are venting outside is getting air from somewhere!!


1. Any proper march, cal, iwaki, etc, or other brand of pump will work provided the voltage and capacity matches the ac requirements.

2. The size range you're in is 110 territory, and a btu is a btu voltage doesn't make it cool any better.

3. There are, but get the reverse cycle. For our 1-2 months of cold it's really nice to have.

4. Do not do this to yourself! You can't tell what sort of life these things have had....they may be fine, but may not.

Go with the 16k unit, too large a unit and you will have short compressor run times. This means cold air, but wet air. The longer the compressor runs, the more times the air passes over the evaporator and the more moisture is pulled out of it.

We're in the same lake and use a 5k ac on our 32' sailboat. During the day it doesn't really keep up with the heat from the sun, but at night it's more than adequate. I chose this size to keep power requirements low and still sleep at night in the marina.
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Old 14-08-2017, 18:01   #9
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Re: AC system sizes?

Quote:
Originally Posted by Sailmonkey View Post
The portable you bought isn't cooling worth a crap because it's drawing hot air in as well as cooling the air. The hose you are venting outside is getting air from somewhere!!

...

We're in the same lake and use a 5k ac on our 32' sailboat. During the day it doesn't really keep up with the heat from the sun, but at night it's more than adequate. I chose this size to keep power requirements low and still sleep at night in the marina.

There's only one exhaust hose on the back of the unit. This is the unit that I have in there now. https://www.amazon.com/LG-LP0815WNR-.../dp/B0115XSHPA


I was surprised that even at night it wasn't cooling. We left at 9pm on Saturday and it was 84 degrees inside. When I went back at 830am on Sunday it was only 82. I dont know how y'all do it with only 5k btu's!
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Old 14-08-2017, 18:07   #10
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Re: AC system sizes?

Quote:
Originally Posted by TooCoys View Post
There's only one exhaust hose on the back of the unit. This is the unit that I have in there now. https://www.amazon.com/LG-LP0815WNR-.../dp/B0115XSHPA





I was surprised that even at night it wasn't cooling. We left at 9pm on Saturday and it was 84 degrees inside. When I went back at 830am on Sunday it was only 82. I dont know how y'all do it with only 5k btu's!


It's not cooling because all the air that blows out of the hose to the outside needs to come from somewhere!! It's coming in from the outside, so that ac is exerting a ton of energy to cool outside air instead of already cooled inside air.

Our 5k will cool the boat overnight to the low 70s. If we put up the sun awning it'll keep the inside around the mid 80's during the day.....not ideal, but nice and dry.
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Old 14-08-2017, 18:14   #11
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Re: AC system sizes?

Quote:
Originally Posted by Sailmonkey View Post
It's not cooling because all the air that blows out of the hose to the outside needs to come from somewhere!! It's coming in from the outside, so that ac is exerting a ton of energy to cool outside air instead of already cooled inside air.

Our 5k will cool the boat overnight to the low 70s. If we put up the sun awning it'll keep the inside around the mid 80's during the day.....not ideal, but nice and dry.


I see what you're saying. That unit is sucking new air into the boat from the cracks and crevices.

Where as a marine unit would be using the same air that would circulate in a loop through the return air vent.
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Old 14-08-2017, 19:13   #12
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Re: AC system sizes?

Quote:
Originally Posted by TooCoys View Post
I see what you're saying. That unit is sucking new air into the boat from the cracks and crevices.



Where as a marine unit would be using the same air that would circulate in a loop through the return air vent.


Bingo!!
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Old 19-08-2017, 04:22   #13
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Re: AC system sizes?

These guys chopped up the bulkhead to add air/footrest.

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1968 Chris Craft Commander 31 ft Hard top Always in freshwater | eBay
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