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Old 13-02-2012, 07:07   #1
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Installing AC in a Cat

Hi,
My wife and I have just bought a FP Belize 43 Duo in Phuket. I am looking to install an AC system but am wondering what is the most cost effective and efficient type installed in Cats of this size, self contained, split systems or chiller unit. I am thinking of going for a 9000BTU self contained unit in each aft cabin and a 16000BTU under the seats in the saloon, run through a 3way duct splitter to cover both forward cabins and the saloon itself.
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Old 13-02-2012, 08:07   #2
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Re: Installing AC in a Cat

Greetings and welcome aboard the CF, Prashanti.

Congratulation on your new boat!
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Old 13-02-2012, 08:27   #3
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Re: Installing AC in a Cat

A major problem is the starting amps required for A/C units. This might be 2 to 3 times the running power consumption which requires an oversized Genny just to start the units. Mermaid claims that their little A/C units will run on a 1000 watt Honda Genny or a battery bank which is just about unheard of.
5,200 BTU System / Air Conditioning / Marine Division / Home - Mermaid Manufacturing - Home of Mermaid Marine Air Conditioning
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Old 13-02-2012, 11:52   #4
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Re: Installing AC in a Cat

I have AC aboard my cat and also run other cats in the charter fleet with AC. Suggestions based upon my experience:

Installing AC in cats can be a pain. Multiple units makes this much easier, but even more convenient, and cost saving, is to use split units and route the refrigerant lines to evaporator grills/fans in the cabins rather than trying to route air duct work. This can save you huge amounts of effort/modifications/dollars/frustration.

The actual AC equipment for a cat is no different than a monohull, but the installation is typically much more involved.

I've run boats with most major brands of AC units and have generally found them all to be quite reliable. They are all of course grossly overprice (just compare cost per BTU to a residential unit), but not much you can do about this unless you have the skills to roll your own.

Also, cats are inherently more difficult to cool. This is because the accommodation areas are more spread out and not contained in a single hull like a monohull. You also have much more area above the water line than you do in a monohull, thus it heats up faster than below the water line space. This is especially true of the deck house which functions like a big green house. This is where you will need the most BTUs. Do the calculations for the deck house area (worksheets available on most manufacturers web site and/or manuals) and then go to the next largest BTU sized unit they have -- at a minimum. External sun awnings and window shades can help dramatically with cooling the deck house.

Just look around your FP think about where you are going to route air duct work that is a minimum of 6" in diameter? The options are quite limited -- routing refrigerant tubing is way easier.

I also suggest not going overboard on the number of units. There is one FP in the fleet here (Belize) which has 6 (yes "six") AC units and a large gen set to run them all...it is a maintenance nightmare -- I have to re-plumb/jury-rig/re-wire something AC related it seems every time I run this boat.

Also, carefully consider the routing of your cooling water and condensate drain hoses and how they might behave underway in heavy weather. I have one condensate drain hose that exits under the bridge deck. In heavy conditions, sea water can be forced back up this hose into the condensate tray. This caused corrosion to form in the tray and nearby components -- had to pull it this year to clean up and repaint (for what they charge for these so-called "marine" units you would think they would be stainless -- nope -- just good old stamped steel that rusts easily in salt water). Installing a valve to close it this year, but a better original install idea would be a venturi fitting to draw condensate out the cooling water drain hose.

Also, the ability to direct cooling where you want it is a big help on a cat. In my installation, I use adjustable vents to do this. For example, during the day when most activity is up in the deck house you may want to focus your BTUs there. In the evening you typically only really care about the cabins. Adjustable fans/vents can help you do this.

My configuration (aboard a Wildcat 35) is one 12K BTU unit which cools the deckhouse and the stb hull. Plus a 10K BTU unit which cools the two port cabins. This is adequate for my boat, but can't keep up with the deck house (without shade awnings up) on a good hot sunny day.
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Old 13-02-2012, 12:31   #5
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Re: Installing AC in a Cat

Belizesailor hit on pretty much every major point, special emphasis to the routing of cooling water and condensate hoses which are the most frequent source of pain for our AC system.

We have a 12,500 BTU mermaid unit in our cat (admittedly a much smaller Gemini 105Mc), and it actually will start up and run very well on the Honda 1000 generator/inverter. Anything larger and you'd need to modify it to start the compressor and fan units separately to spread out the starting load.

Good Luck and Congrats on the new boat!
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Old 13-02-2012, 17:19   #6
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Re: Installing AC in a Cat

I have (2) 16k btu cool/reverse cycle units on my Belize maestro. One sits under the salon seat just port of the mast. This unit has a hose to an outlet directly above in the salon, a hose to the starboard hull above the desk, and a hose to the port forward stateroom (high on the bulkhead above the shelf). A second AC is under the helm, the shelf unit inside the salon is cut down to only 2" deep. This unit has an outlet between the helm instrument access cover and the starboard hull door, and outlet in both the port and starboard aft staterooms. The port stateroom hose runs through the floor locker in the cockpit via an insulted duct with a weatherproof hose over it.

I run both off a Mase 7.6is genet without any problem.
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Old 13-02-2012, 18:17   #7
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Thanks Belizesailor, some good info there. I like the idea of Dotdun, to install two larger self contained units in the salon and the get clever with the ducting. Saying that though, I can see the advantages of using splits in each engine room an then only having to route refrigerant lines. Are the split system cabin air handling units large?
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Old 14-02-2012, 07:20   #8
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Re: Installing AC in a Cat

Quote:
Originally Posted by Prashanti View Post
... Are the split system cabin air handling units large?
For instance: 16.50/419 High x 21.25/540 Wide x 15.60/396 Deep
http://www.dometic.com/7b2dbf54-db6d...a67d520e.fodoc
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Old 14-02-2012, 08:45   #9
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Re: Installing AC in a Cat

Quote:
Originally Posted by Prashanti View Post
Thanks Belizesailor, some good info there. I like the idea of Dotdun, to install two larger self contained units in the salon and the get clever with the ducting. Saying that though, I can see the advantages of using splits in each engine room an then only having to route refrigerant lines. Are the split system cabin air handling units large?
You're welcome.

Generally the split units are not physically larger -- they just separate the components.
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