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Old 30-06-2004, 13:10   #1
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Air Conditioning

Having moved our boat to Florida, I am considering putting an air conditioning unit onboard. I have a portable 5k BTU unit. It helps take the edge off, but does not do a sufficient job for a live aboard situation, which we are contemplating. Using 14 BTU per cubic foot as reccomended on as couple of web sites, I calculate a need of 25,000+ BTU for our 37' Prout Catamatan. This seems a bit large. From a physical size perspective, I would like to stick with one of the compact 16,000 BTU units.

I am interested in any real world experiences of AC size vs. boat size. I would also like to hear any brand specific experiences.

I plan on doing all of the install work myself. I already have a nice central diesel heater, and may tie into the existing duct system, with a couple modifications. I am planning on a water cooled unit and will use an existing washdown water seacock, with a Tee and separate valve.

Thanks, Woody
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Old 01-07-2004, 03:12   #2
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AC Sizing

Woody:
It’s difficult to accurately size Air-Conditioning for Live-Aboard Catamarans in the sub-tropics.
I’ve successfully used about 15 Btuh cooling per cubic foot, for liveaboard Monohulls in south Florida. Catamarans (as you know) are different.

The “rule of thumb” recommendations (baseline ± 14 Btuh per cubic foot of area) must be modified upward to consider:
1. Ambient air & water temperature
2. Glazing
3. Solar Exposure
4. Occupancy and Activity Loads
et al

South Florida marinas will experience 100 Deg F (humid) air, and 85 Deg water temperatures. Add about 10% to total calculation.
Catamarans, like your Prout , have extensive glazing. Add about 500 Btuh per square foot of screened & curtained “windshield”.
Catamarans have huge horizontal surfaces exposed to the sun, and also require longer air ducts to distribute the air. Return-Air is also more problematic. Add ...
The more people in a boat (occupants), the more cooling required. Add about 300 - 500 BTUH/person for live-aboards (who cook).

Your existing Heating ducts may be inadequately sized for an effective Air-Conditioning system, in your application (sub-tropical liveaboard). Most boats have ducts that are too small for the required air delivery (cfm), and grilles that restrict the free area to 50% or less of the (already too small) duct capacity.
You may not have an effective Return-Air System.
You may not have Zone Control - balancing dampers that allow you to reduce air supply to unoccupied staterooms during the day, and to the salon at night (cooling only the areas in use).

I doubt that a 16,000 Btuh A/C unit will effectively cool more than your main salon, and wouldn’t be surprised if an on-site A/C expert (your equipment supplier) recommended over 30,000 Btuh for whole boat day & night cooling. This might consist of Two Air-Conditioners, sized at about 16,000 Btuh EACH.

Given your statement that 5,000 Btuh “takes the edge off”, and your spatial constraint to about “16K Compact” unit size - I’d suggest that you will have to settle, and may be nearly content with/for less than “residential quality” air conditioning - a not uncommon marine situation.

Notwithstanding the multitude of cruising & liveaboard advantages they offer; Catamarans are a “bitch” for tradesman.

HTH
Gord
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Old 02-07-2004, 08:29   #3
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I may have to compromise and only cool the main salon in the day during the summer. Then cool the entire boat at night in the summer and all day the rest of the year.

I do not want to install two units. It would take too much storage area. The largest unit I could install would be a 20k BTU unit, although the installation would be very tight and a 16k unit would fit better. I may also be faced with upgrading my 30 A service to a 50 A if I go with a larger unit. So, I guess maybe my real question is "what is anyones real experience with a 16k BTU unit on a boat similar in size to mine?"

BTW, I live in North Florida. The summer temps are slightly cooler than South Floirida and it can get down right cold in the winter. The glazing on the Prout is not quite as bad as most cats, although it is definitely worse than a monohull. I will probably intall a tarp system for shade during the hottest time of year.
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Old 14-07-2004, 09:02   #4
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we just finished the grand air conditioning project on our 1999 St. Francis 44. it was a bigger project than we thought in every way (scope, budget, and time) and we hired professionals... but in the end it is WELL worth it!!! FYI we have 2 units for our 44 foot cat (24 beam, lots of windows and hatches bringing in heat gain too). One 16,000 btu for the main salon and forward master sized cabins. One 12,000btu for galley and smaller aft cabins. This seems to be perfect, and on many days I am gleefully downright cold if I set the temp right. If you want more details feel free to contact us. Best of luck to ya!
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Old 14-07-2004, 09:22   #5
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In conversing with Pa La O La, another Prout 37 owner he feels that his 12k BTU unit is keeping up Ok. He is just on the other side of Florida from me and in the same basic climate. Given you have 28k btu total and nearly twice the volume and surface area of our boat, I am leaning towards a single 16k btu unit.

Thanks for the input. It really helps to have some real world reference points.

Did you have AC on your PDQ?

Woody
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Old 14-07-2004, 21:32   #6
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Perhaps more in the nature of an inquiry, rather than a suggestion. Is there a sufficient difference in the typical Florida water temperature as the depth increases to consider bringing the cooling water up from deeper so as to increase the efficiency of the AC system?

Example: If the dockside depth is ten feet deeper than the location of the thru-hull cooling water intake, and the water temperature is ten degrees cooler down there, would it pay to plumb a tee fitting into the system to which a length of hose could be threaded?

Someone will have to work out the "mechanics".
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Old 15-07-2004, 08:45   #7
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I don't know the answer of temp vs depth at my location. I am guessing it is not significant. We have about a six foot tide and twice a day it mixes things up pretty well. You might have a couple of degrees difference due to solar heating late in the day. The friction in the hose would add to the suction head seen by the pump and may slow the flow down a little.
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Old 16-07-2004, 07:24   #8
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Just for what its worth....

Our Jeanneau 40 3 cabin had Air Conditioners installed by the previous owner about a year prior to our purchase. They had the installation done by a fairly reputable SW Fla company and chose two Marineair units: a 12,000 BTU for the main cabin and forward cabin and a 8,000 BTU for the aft cabins. They installed one through-hull for the intake and one pump with a Tee fitting to supply both units. Each unit has its own outlet through-hull above the waterline.

This configuration does a great job of keeping the boat cool during a Florida summer.

Some of my lessons learned and concerns:

1) If I was making the purchase, I'd pay attention to the noise and location of the units. Much of the noise is associated with inadequate vibration dampening of the main units, I think.

2) Inspect some other installations for ideas. Although mine was supposedly professionally done by a reputable firm, I have to say it is a half-assed job. Much of the ductwork wasn't secured properly, power supply wire was lying loose in the bilge (routed through the sump!), and the water pump is wired to run all of the time that the first AC is turned on. This means that I can't run only the aft AC and, I think, is also going to wear out the pump prematurely. Additionally I think they installed the cheapest pump they could find.

3) The Marineair units don't seem to be very ruggedly finished. I'm already finding some rust/corrosion in the drip pans and on the actual units.

Just another data point for you.

Curtis
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Old 17-07-2004, 03:30   #9
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Augie Byllott - thefantasea:

I don’t think a deeper water A/C cooling water intake is likely to be of any practical benefit:

1. A/C Pumps (‘March’ etc) are notoriously expensive, “finicky”, and subject to sudden failures. I wouldn’t want to compromise my cooling water system by adding suction head (load) to the pump intake. As Exposure indicated, this head would result from Frictional losses (not lift), due to 10 feet of external pipe & attachment fittings (hose, whatever), unless you forgot to bleed the snorkle.

2. I cannot visualize an elegant (simple & effective) mechanical arrangement to extend the thru-hull intake downward. I’d be very interested in anyone’s ideas.

3. You’re unlikely to find a boat slip with 10 or 15 feet of water depth (MLW).

4. You’d need more than a few degrees of Delta T, for the deeper intake to have an appreciable cooling benefit. How common are (say 5 or 10 degree F) thermoclines at <15' depths(in warmer A/C locals) ?
A simple swimming pool thermometer should reveal your actual conditions. Float it and record surface temperature. Sink it, and record (several) sub-surface temperatures at various depths.

HTH
Gord
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Old 17-07-2004, 04:06   #10
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Bad A/C installations

CURTIS:

1. Location & Noise:
Most of us don’t have much discretion in choosing locations for larger equipment, such as Air-Conditioners & pumps etc.
I’d agree with you, that the first principle of noise control is vibration isolation for all rotating equipment.
The second cause of controllable noise is air-movement in ductwork and discharge grilles. The duct must be large enough to accommodate the design air-volume at a reasonable velocity, and must not be constrained at the discharge grille. Accoustic insulation, inside the duct, greatly reduces sound transmission. Round corrugated flex duct (as is common) is a poor choice.

2. I agree that you describe very poor tradecraft in the P.O.’s installation. Loose ductwork, and wiring in the bilge (etc) isn’t right - it isn’t even wrong! Would you know (& be willing to name) the P.O.’s installer?

3.Manifolded cooling pumps (1 pump & 1 inlet cools 2 or more A/C units) are the commonest approach to multiple-unit installations.
The raw water intake must be properly sized to accommodate both condensers operating (about 1.5 time diameter of largest hose after “Tee” to A/C condenser.
The pump should be set up to run when either A/C thermostat calls for cooling (relay). This is not rocket science.

4. There are several different types of pump commonly used on A/C systems:
- Bronze-Impeller Pumps, high GPH for multiple unit applications.
- Self-Priming Centrifugal (install below waterline /w continuously ‘uphill’ piping to condenser) pumps, highest GPH for multiple unit applications.
- Rubber-Impeller pumps, for dedicated single unit applications.
- Magnetic Drive Pumps - I HATE them - expensive, water-cooled (failure prone), limited head, etc.

5. Specific products: I’m getting out of date, and my memory is fading - but I don’t recall any particular problems associated with “Marine-Air” units.

with sympathetic regards,
Gord
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Old 17-07-2004, 08:05   #11
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Re: Bad A/C installations

Quote:
GordMay once whispered in the wind:
CURTIS:

-- Clip --

2. I agree that you describe very poor tradecraft in the P.O.’s installation. Loose ductwork, and wiring in the bilge (etc) isn’t right - it isn’t even wrong! Would you know (& be willing to name) the P.O.’s installer?

3.Manifolded cooling pumps (1 pump & 1 inlet cools 2 or more A/C units) are the commonest approach to multiple-unit installations.
The raw water intake must be properly sized to accommodate both condensers operating (about 1.5 time diameter of largest hose after “Tee” to A/C condenser.
The pump should be set up to run when either A/C thermostat calls for cooling (relay). This is not rocket science.

-- Clip --

Gord,

re: #2 As to naming the company, I would backchannel with anyone interested. I've been around the service business long enough to know that poor work isn't always the fault of the installer and would hate to trash them publically without full disclosure.

re: #3 Where would I look for instructions on connecting up a relay to the pumps as you describe. Right now the pump runs the entire time the main unit is turned on. The aft unit just assumes it is on.

Thanks,
Curtis
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Old 18-07-2004, 03:22   #12
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Pump Relay Controls

PUMP RELAY PANELS:

Whatever you buy should come with an installation & instruction manual, including wiring diagrams. Although you (or your electrician) could design/build your own custom Pump Relay Controls, it might be cheaper (& certainly easier) to purchase a purpose made control from you’re A/C manufacturer. They'll need to know the details of the A./C Units, Pump, and Thermostats.

Marine Air has lots of installation manuals on-line at: http://www.marineair.com/

Aqua Air has lots of good information at: http://www.aquaair.net/
including their AQPR Pump Relay Panels at http://www.aquaair.net/80085-AQP2R-AQP8R.pdf

HTH
Gord
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Old 18-07-2004, 15:33   #13
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So I presume you guy's operate these AC's when tied to dock. I presume they are power hungry devices, just like any refrigeration? But just incase not, HOW do you maintain the power demands?
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Old 18-07-2004, 18:50   #14
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Just at the dock for me. I thought I was going to go for a genset but have talked myself out of it.
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