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Old 16-07-2009, 17:46   #1
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Lets Talk Air Conditioning - Size Matters

Ok folks, let us talk and share about air conditioners, and powering same in areas where there is no shore power. Is yours big enough? How big (BTU) and in what boat. I do not want to make the wrong move in Texas heat. Does yours work good enough. Seems 12000btu is popular for sailboats between 30 and 40.

Here is a topic that was discussed earlier. Generators..Honda 2000 watt portable generator rated at 16.8 amps @ 120 has leads to double up so you have 33.6 amps @120. More than enough for 16000BTU. At what point, (size of boat) is it necessary to move up to 16000BTU on a sailboat in a blistering climate? They weigh 47lbs.

I was quoted $950+- for each. Warranty 3 years. Since you would only need them on the hook when no shore power was available then they seem a pretty good option, you can barely hear them even standing next to them. So small you can fire one up for the refergerator or to charge up batteries. 12 volts 8 amps x 2= 12v 16 amps.

For the price of one marine diesel installed you can buy a lot of hondas for occasional use. Yeah I know about gas on board, but if handled responsibility..... And there is the added bonus to use them elsewhere.

Just a thought.
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Old 16-07-2009, 20:17   #2
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The heated area on a pontoon boat is substantial and despite the relationship between BTU and calories/cooling energy, any analogy to be made between a square boat and a sail boat is essentially meaningless.
I'm also not sure I'd say my Honda 2000 is barely audible when standing next to it. It is quieter than any similar sized genset with which I am familiar but two of them is definitely noticeable.
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Old 16-07-2009, 20:31   #3
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The heated area on a pontoon boat is substantial and despite the relationship between BTU and calories/cooling energy, any analogy to be made between a square boat and a sail boat is essentially meaningless.
I'm also not sure I'd say my Honda 2000 is barely audible when standing next to it. It is quieter than any similar sized genset with which I am familiar but two of them is definitely noticeable.
Now that is only if you have them set up for surround sound. I am concerned about a lot with the pontoon boat, but my mind is eased somewhat since I put the radar, auto pilot and plotter all as an integrated team.
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Old 16-07-2009, 20:34   #4
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Quote:
Originally Posted by Mule View Post
Ok folks, let us talk and share about air conditioners, and powering same in areas where there is no shore power. Is yours big enough? Generators..Honda 2000 watt portable generator rated at 16.8 amps @ 120 has leads to double up so you have 33.6 amps @120. More than enough for 16000BTU. At what point, (size of boat) is it necessary to move up to 16000BTU on a sailboat in a blistering climate?

Just a thought.
You must be kidding, two 2000 Watt Honda generators to cool a boat at anchor.
You will never be able to enjoy all that cool air, you will be fetching Gas.

Get a hammock and a suncover for the boat. Enjoy the breezes and not the 60 Hertz Hummmmmm.
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Old 16-07-2009, 20:38   #5
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Mule
I think 12000 is a good size for 30-40 but it depends on the boat and layout, some boats do better with 2 6000 btu. just a warning - I am pretty sure bigger isnt nec better, if you over size the ac it will not cycle properly, and then bound to break....we have reached the pateau of my ac knowledge . Really, I wanted you to know that there is a brand new (in the box) mermaid 12000 btu for sale at my marina (half the price of a new one), pm me if you want to check it out. But it might be a bit premature, your new boat may have one already
Erika

ps the seller is not related to me in any way - dont know the guy - no commission, just happen to notice the for sale ad in my marina bulletin
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Old 16-07-2009, 20:40   #6
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We had a 33 ft boat with 12,000 and it was not enough. Our current boat is 36 and 16,000 is about right.

Quote:
Here is a topic that was discussed earlier. Generators. Honda 2000 watt portable generator rated at 16.8 amps @ 120 has leads to double up so you have 33.6 amps @120. More than enough for 16000BTU.
Not even enough to be close. What a Honda 2000 will put out (nice generator BTW) won't start any AC you can install and be cool. At 4000 you might get close, but it won't do 16,000 btu's in your dreams. I doubt two would do it either. The starting amps required on an A/C is more than these will sustain. Under voltage would trash them given the loss to the Inverter required to power them. They really want AC voltage. At three you might be in the ball park. There you ultimately die since the fuel tanks are too small and the noise times three is worse.

The concept of A/C on the hook is false unless you have the serious genset. You then pay the price of the purr of a diesel engine. Silence in heat is better or find a higher lattitude. Running a genset all night is not occasional use. The Hondas barely make it recharging batteries. They work well for the time you need them and then shutting them off. If all this worked no one would own a real generator.
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Old 16-07-2009, 21:30   #7
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47' with a 15,000 and a 12,000 btu units. They are barely enough on 100 degree days.
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Old 16-07-2009, 21:30   #8
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Paul,

I wonder if the 2 hondas (2000 super quite) hooked up in parallel gives the 2x the power the specs say. From what I saw on the various websites for AC's the momentary start amps required was doable if no one is inflating their specs. They said 1.8 x run amps. That was generally around 10 to 13 run amps so with 2, 2000 it should do it if the manufactures are not fudging.

As for gas usage, well Honda gives some impressive claims.

Honda Power Equipment - EU2000i
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Old 16-07-2009, 21:47   #9
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Mule
I think 12000 is a good size for 30-40 but it depends on the boat and layout, some boats do better with 2 6000 btu. just a warning - I am pretty sure bigger isnt nec better, if you over size the ac it will not cycle properly, and then bound to break....we have reached the pateau of my ac knowledge . Really, I wanted you to know that there is a brand new (in the box) mermaid 12000 btu for sale at my marina (half the price of a new one), pm me if you want to check it out. But it might be a bit premature, your new boat may have one already
Erika

ps the seller is not related to me in any way - dont know the guy - no commission, just happen to notice the for sale ad in my marina bulletin
Also if your unit does not cycle properly the air will not have the moisture wicked out of it and you air will be cold and clammy. What size are you running on your 30CD?
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Old 17-07-2009, 02:21   #10
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Sizing Air-Conditioning:

A “rule of thumb” recommendation for sizing marine air-conditioning is about 14-to- 15 BTU/h per cubic foot of cabin volume.
More glazing, pilot house, etc = more heat gain; so perhaps up to 17 BTU/h per cu. ft.

A professional will size the air conditioner based on the latent cooling load (which considers the relative humidity of the air), as well as the sensible cooling load (which considers the outdoor & indoor design air temperatures) for your boat & location.
A (theoretically) perfectly-sized air conditioner will run continuously during the hottest 2.5% summer design (outdoor) temperatures.

Don't buy an oversized unit. An over-sized unit short-cycles (turns on & off too rapidly), so doesn’t properly de-humidify*, and uses more energy (starting currents).

On the other hand, make sure any ducting is sized large enough to allow low-velocity air distribution.

* The ability of the air conditioner to remove moisture (latent capacity) is lowest at the beginning of the air conditioner cycle. The moisture removed from the indoor air is dependent upon the indoor coil temperature being below the dew-point temperature of the air. The moisture then wets the indoor coil and, should the unit run long enough, will begin to flow off the coil and be removed out of the condensate drain. For short cycles (< 10 min, or so), the coil does not have time to operate at the low temperature, and when the unit stops, the moisture on the coil evaporates back into the indoor air. Thus, in humid climates, a properly sized air conditioner will do a far better job of removing moisture from the air than oversized units.
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Old 17-07-2009, 05:53   #11
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Mule,

The little Honda's really are nice and Honda specs are about as good as they get. It's just not a generator for running all night. Totally maxing the generator is required and it won't realistically work over any long term situation. The compressor cycles so it's not that it just starts when you flip the switch and settles in. A good AC unit will run a good long time to cool things off then cycle and keep the fan running all the time. Ours steps the fan up and down too. It also requires a LOT of gasoline and you just won't have that kind of storage for gasoline in addition to diesel and water.

Gord's numbers are the way the real pros do it. 12,000 BTU's is not enough for a 30 - 40 ft boat. Undersizing the AC will basically means it runs all the time and never cools the boat. Our last 33 had a 12,000 but the deck was solid glass and heated up. That unit in very hot weather could not really do the job until well in 100 degree days. It could do maybe 85 at best running all day long.

The heat side of the reverse cycle was great however and worked down to a water temp near the mid 40's.

The awning helped. Awnings are something you should just have any way. If you can cut off the sun you can then cool the boat naturally a whole lot easier. A little breeze off the water and it's pretty nice even on a hot day.

Our current boat at 36 ft has a 16,000 and that is about right if not perfect. Over 40 ft and you need two units. It also has a large water pump. The pump is not in the electric numbers on the AC unit. You want a big pump that shoots the water out the outlet not dribble. The March is a really good one and a Cal is poor.
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Old 17-07-2009, 08:14   #12
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A friend set up a pair of the Honda 2000 units on his Camano 31 LOA trawler. The pair powered his marine 16000 btu A/C unit fine.
They are not too big but a pair does take up a good bit of space his were in the cockpit.
Steve
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Old 17-07-2009, 08:50   #13
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My step-son runs his 2KW with the fuel line to a 6 gal tank.

Generator Fuel Tank
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Old 17-07-2009, 10:13   #14
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Well, well, for occasional use at anchor this might work after all. I need to to have a look see if the 3 year warranty is fool proof. I kinda think Honda has an out, they did not become as big and successful as they are by leaving many open doors.

I had given this up until the Camano story came out. I chartered one in BC a few years back, great boat.
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Old 18-07-2009, 07:37   #15
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too much power

so here's a wacky twist to this thread; I've fixing up this 63' steel boat and installed a 20k Northern Lights genset for electrical power. I figured hey why not, that's the size all the other boats down here in the oil patch use. So now comes the time to crank up the genset and I get around to reading the instructions and they say I need to load the generator to 75% of its load capacity to break it in and make sure the piston rings seat properly. Now I sit down to do the math. I'm not making this up.

I always planned to cool off with big open windows which I now have and no insulation on the steel walls, the roof is bright white and partially shaded. Seems like, short of throwing to two leads into the salt water and frying the whole marina, the only thing that will draw anywhere near that kind of power will be the air conditioner from hell, a 5 ton 60,000 BTU behemoth that will draw 35 amps at 240v and even then I'll have to turn on everything else I can find.

Good thing I love the smell of diesel in the morning, noon, and night.

The gen set is welded into the engine room and keel coolers and the hatch I used to install it is welded over. It is not coming out, besides I've become quite fond of it, even though I've never turned it over. It looks really cool. So now I have this air conditioning unit on order and it will be here in a few days.

I'll let you know how it all works out and when I'm coming your way.
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