A/C Sizing and Recomendations - SailNet Community
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post #1 of 14 Old 03-19-2010 Thread Starter
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A/C Sizing and Recomendations

We are thinking of adding air conditioning to our 1984 Pearson 303. The boat is 30'3" LOA, with a 10'11" beam. We sail primarily in the Chesapeake area. Our primary motivation is to cool the cabin and take down the humidity at night when at the dock. We would seldom use it during the day, but if we did, we'd be happy if it could bring down the interior temp by 10 to 15 degrees max and lower the humidity a bit. We don't want, and don't expect, to keep the boat at 50 or 60 degrees in the summer, and we don't want to be sleeping under blankets. We will also likely sew an awning this year to keep the sun off the decks (I've heard that this can amount to a 10 degree temp difference). I mention this because it is important to our AC size calculations.

Based on the above, do people think a 9,000 btu water cooled unit would be sufficient for our specific needs? We'd rather not go to 12k or 16k btu because of size, weight and power consumption (we only have 30 amp service and small space to install the unit). Secondly, what do people think about the Webasto FCF units? They look to be well built and the price is reasonable, but I'm not all that familiar with their track record. We plan to keep this boat for another five years or so. And for the purists, we don't have a generator and have no intention of using the AC on the hook.
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post #2 of 14 Old 03-19-2010
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We have Marine Air 16K and 8K BTU units on a 40 Ft boat on the Chesapeake.

My hunch is that the 9K will be overly taxed on a 30 Ft.

also see: How to size HVAC

Here are some installer sizing estimates from our experience back in 2002:
550-650 BTUs/ cubic meter for areas that are used during the heat of the day.
380-410 BTUs/ cubic meter used after sunset

Wayne
s/v Virginia Dare

Last edited by wwilson; 03-19-2010 at 01:08 PM.
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post #3 of 14 Old 03-19-2010
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I just asked this question.......maybe togather we can get it figured it out.

How to size HVAC

"Go Simple...Go Large"

Relationships are everything to me..everything else in life are just tools to enhance them.


The purchase price of a boat is just the admittance fee to the dance...you still have to spend money on the girl...so court one with something going for her with pleasing and desirable character traits others desire as well... or you could find yourself in a disillusioned relationship contemplating an expensive divorce.
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post #4 of 14 Old 03-19-2010 Thread Starter
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Quote:
Originally Posted by Stillraining View Post
I just asked this question.......maybe togather we can get it figured it out.

How to size HVAC
Yes, I've been following you thread, but I didn't want to hijack given that with our smaller boat our specs are quite different that yours. Do you have any thoughts on the different suppliers?
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post #5 of 14 Old 03-19-2010
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Nope ..total newbie on the subject....for me it will boil down to what they are willing to pay for.

"Go Simple...Go Large"

Relationships are everything to me..everything else in life are just tools to enhance them.


The purchase price of a boat is just the admittance fee to the dance...you still have to spend money on the girl...so court one with something going for her with pleasing and desirable character traits others desire as well... or you could find yourself in a disillusioned relationship contemplating an expensive divorce.
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post #6 of 14 Old 03-19-2010
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I would think a purist would use oil lamps and a hand held fan.
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Brian
Living aboard in Victoria Harbour
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post #7 of 14 Old 03-20-2010
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I can tell you that I have 16k BTU water cooled reverse cycle (MarineAir) on my J/28. It is sufficient on those 90deg + humid Aug days on the Chesapeake, but cycles often in those conditions. I am not sure I'd want to go less. My installation is under the V-berth...it does not wake me up, but if you are a light sleeper....YMMV.

I am also using 30AMP service and have zero issues. My electric bill was <$50 for the entire season.

I see you are located in DC....can I ask where you keep your boat? I am looking for a new home this season on the Western Shore.

Jason
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post #8 of 14 Old 03-21-2010
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I do not know if all brands have a stepped turn on feature, but when I added a 16K unit to my 36' boat the installer recommended one that had this feature.

My unit has a single compressor with two separate heat exchange units, one forward and one aft. The system is set to turn on the pump first, then the compressor and finally the fans. This makes sure that the 30 amp service is not overwhelmed with a voltage spike at turn on.

I would check on this if you are sticking with the 30 amp service.

On your original question, I think you could get by with something less than a 16K unit, I doubt if there is much price difference between that an a 12K unit.

By the way, you are using the term air conditioning, but I assume you mean heat pump unit. On the Chesapeake, heat is just as essential to extending your season as cooling. Let the purists suffer, I have really enjoyed the comfort the heat pump provides.

I went so far as to add a diesel generator so I could use it on the hook. In the summer, sailing is great when you are outside, but it can take hours for the inside of the boat to cool down enough to sleep. We like to anchor out, so at the end of a sailing day, we would crank up the AC, do our cooking while it was on to avoid heating up the cabin, then shut it down and open up after sun was down.

Herb DuBois
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post #9 of 14 Old 03-21-2010
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Quote:
Originally Posted by HerbDB View Post
By the way, you are using the term air conditioning, but I assume you mean heat pump unit. On the Chesapeake, heat is just as essential to extending your season as cooling. Let the purists suffer, I have really enjoyed the comfort the heat pump provides.

I went so far as to add a diesel generator so I could use it on the hook. In the summer, sailing is great when you are outside, but it can take hours for the inside of the boat to cool down enough to sleep. We like to anchor out, so at the end of a sailing day, we would crank up the AC, do our cooking while it was on to avoid heating up the cabin, then shut it down and open up after sun was down.
Exactly our plan of usage..although we love to BBQ and use that more then any inside cooking..But I could not agree more with the little cooling off of the cabin thing... There is nothing worse for us then lying in sweat trying to get to sleep...My purest days ended at 26 with two ruptured disks in my back...TEHO

"Go Simple...Go Large"

Relationships are everything to me..everything else in life are just tools to enhance them.


The purchase price of a boat is just the admittance fee to the dance...you still have to spend money on the girl...so court one with something going for her with pleasing and desirable character traits others desire as well... or you could find yourself in a disillusioned relationship contemplating an expensive divorce.

Last edited by Stillraining; 03-21-2010 at 11:28 AM.
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post #10 of 14 Old 03-21-2010
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I have a Webasto 16000 BTU sitting in the living room awaiting installation -had to rewire first- under the v berth of my 303...To the increasing irritation of "The Admiral." It is replacing an old Cruiseairr that was doing little other than making noise and water.

The 303 has a bigger cabin than most 80's vintage 30 footers BTW. Theres a bigger bunch of cubes in that cabin compared to a contemporary Catalina 30. That said, I may rue not going with the 12000 btu instead.

Anyway, hope to get it done before the end of April, and can report back then.

-Forgot to add... I am in Houston, and the marina is in a bowl, ripe for maximum heating...

Last edited by sidmon; 03-21-2010 at 05:06 PM.
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