Thoughts on Air Conditioning J/40

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Chris Leo

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Jan 22, 2026, 2:16:40 PMJan 22
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Hi all,

We have J/40 "Cowbuoy" based in Annapolis, and while we've endured some warmer summer nights before, the bottom line is we have to be very choosy and we'd like to be able to use it more now that our daughter is entering sailing camp (and we live an hour away).

I walked through the boat with an A/C technician recently and the conclusion is that there just isn't the right amount of workable space for an integrated unit, especially considering the amount of space needed for the ducts to pass through the bulkheads or anywhere near where it needs to be distributed.

I've looked at hatchtop units but not sure if anything is practical. Surely there's another J/40 owner out there that has solved this issue? Help, please!

William C. Wohlforth

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Jan 22, 2026, 5:11:37 PMJan 22
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Chris,

My J/42 Hotspur was an Annapolis boat LEGACY, and she came with reverse cycle AC, neatly installed at factory.   I am not up to speed on precise interior differences between these boats, but this installation has a AC unit in stb lazarette and one under stb V berth, with ducting running to q-cabin, main salon and f’csle.  As I say, very neat and trim.  Can say more, but could be J/42 is not relevant to your 40.

Sadly, in Maine, I have no use for it and am likely to pull it all out . . .

Bill

From: j4x-owne...@googlegroups.com <j4x-owne...@googlegroups.com> on behalf of Chris Leo <christop...@gmail.com>
Date: Thursday, January 22, 2026 at 3:16 PM
To: j4x-owne...@googlegroups.com <j4x-owne...@googlegroups.com>
Subject: [J/4X-owners] Thoughts on Air Conditioning J/40

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Todd Stevens

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Jan 22, 2026, 5:29:52 PMJan 22
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I had the same thought.  Except nobody ever sleeps aft, so I just installed a unit under the V-berth.  Ducts run through the head and hanging locker cabinets to the main cabin. Didn’t mind the lost storage space because I’ve removed the forward holding tank, leaving plenty.  

Although I’m rarely at a dock so don’t use the AC much. I have more experience with the same unit in my old boat.  The dehumidify function can be a lifesaver in the muggy season.  The reverse cycle heating is greatly appreciated in the shoulder seasons.

Speaking of the previous boat, space was a problem, so I built a cabinet for the AC unit in the V-berth that kind of tucked in to the curve of the hull.  It took a few inches from the sleeping platform but less than you might think.  The AC unit sat in the wide corner of the bunk on the side that I didn’t sleep on.  I made the mattress cushion to fit around it.

Todd

ray

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Jan 22, 2026, 5:36:00 PMJan 22
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I used Horton Marine to install reverse cycle AC on LucyBelle #63 back in 2019.  Unit was in starboard forward locker and under v-berth.  They did great work. 
Sent from my iPad


On Jan 22, 2026, at 5:11 PM, William C. Wohlforth <William.C...@dartmouth.edu> wrote:



ray

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Jan 22, 2026, 5:38:34 PMJan 22
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Sounds like my install.  And mine would run off my Honda 2000 when at anchor. For heat or ac. 
Sent from my iPad


On Jan 22, 2026, at 5:29 PM, 'Todd Stevens' via J/4X Owner's Group <j4x-owne...@googlegroups.com> wrote:

I had the same thought.  Except nobody ever sleeps aft, so I just installed a unit under the V-berth.  Ducts run through the head and hanging locker cabinets to the main cabin. Didn’t mind the lost storage space because I’ve removed the forward holding tank, leaving plenty.  

Todd Stevens

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Jan 22, 2026, 5:54:33 PMJan 22
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Yes, mine will run off the generator. I also installed a “soft start” module but not sure it was really needed.  The problem being that I don’t carry enough gasoline to run the generator for more than a couple of days.*  It’ll also run off the batteries/solar installation, but not all night. And then you start the day with flat batteries.  

*The other problem being that people who run generators for a couple of days in an anchorage are not popular with the other cruisers.  

Todd

Walter Caldwell

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Jan 23, 2026, 9:47:30 AMJan 23
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Installed a cruisair 16000 btu under the vberth on J/40 #7 in 2008. It is ducted into the forward cabin and into the saloon. Worked great in the Texas heat, but does not cool the aft cabin great. 
Tried it with the Honda 2000 but the startup surge tripped up the generator. A soft start would probably fix that. 
The boat is in Oxford now. Let me know if you want to see the install.
Walter
Sent from my iPhone

On Jan 22, 2026, at 12:16, Chris Leo <christop...@gmail.com> wrote:


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Fred Hawes

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Jan 23, 2026, 10:02:23 AMJan 23
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Hey guys,
I read with interest. Anona, J-46, Coronado. I would just add that my Mastervolt one lung Kubota genset, has been a maintenance headache with few spare parts available and not really enough power to do much, FITS great though!
If ever I want a genset again, it will be bigger, probably a three banger Northern Lights,
Fred hawes


Larry Romano

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Jan 23, 2026, 11:07:03 AMJan 23
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image0.jpeg

I removed the sit down navstation and made this. Top loading isotherm, AC unit 110v and a 300 amp hour lithium.
On Jan 23, 2026, at 10:02 AM, Fred Hawes <fred...@sbcglobal.net> wrote:



Todd Stevens

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Jan 23, 2026, 12:41:52 PMJan 23
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> On Jan 23, 2026, at 09:06, Larry Romano <j40r...@gmail.com> wrote:
>
> <image0.jpeg>
>
> I removed the sit down navstation and made this. Top loading isotherm, AC unit 110v and a 300 amp hour lithium.
>> On Jan 23, 2026, at 10:02 AM, Fred Hawes <fred...@sbcglobal.net> wrote:
>>
Interesting idea. And nice work!

But I like my sit-down too much, I think.

Chris Leo

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Jan 27, 2026, 4:31:09 PMJan 27
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Thanks Walter, very helpful. Is the boat accessible this winter?

To view this discussion visit https://groups.google.com/d/msgid/j4x-owners-group/5C07744F-8491-42C5-B0B1-93CC0D6C175B%40gmail.com.


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Sue Mikulski

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Jan 27, 2026, 6:36:00 PMJan 27
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Paul put A/C under our V berth, same went into main salon and not aft cabin.   I thought it was noisy however in the v berth.  (J/42 #25 ). But ear plugs work, when you need it you are grateful esp on the Chesapeake in the summer.  I think it was a Johnny Clark at Annapolis Harbor yacht yard  

We sold her in Sept sadly 

Steve Rowell

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Jan 27, 2026, 6:57:58 PMJan 27
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Someone got a great boat!

To view this discussion visit https://groups.google.com/d/msgid/j4x-owners-group/4630A60F-DD7C-4509-BEA3-835FCDEA7F5D%40gmail.com.

Sue Mikulski

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Jan 27, 2026, 9:29:58 PMJan 27
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 Yep, a wonderful young family with a 7 and 9 yo, totally into racing, optis, J/29 in Cambridge and the J/42 to live on in Annapolis when the kids sail out of AYC.  The 9 yo told his Dad he would give him $100 deposit to hold it.  First heard from this guy listing it on FB market!  They will update it to what she needed.  Super excited for them. 
Demeter is the new name, a Greek godess I think?

On Jan 27, 2026, at 6:57 PM, Steve Rowell <stevero...@gmail.com> wrote:



Steve Rowell

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Jan 27, 2026, 10:36:41 PMJan 27
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Very nice! Great to see her go to a young family that’s so interested in sailing. Hope you and Paul are well.  Steve

Sean O'Connor

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Feb 1, 2026, 11:36:47 AMFeb 1
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Chris - no good idea on AC, but we are also in Annapolis and the summer heat had curbed our usage. 

A dock neighbor turned us on to a 12V mattress pad cooler that has been a game changer, particularly for my wife. We mounted the small heat exchanger unit in forward head. Astonishingly, just having the pad made sleeping aboard at the dock or on the hook absolutely tenable again. Never would have believed it. Another option FWIW.


Above link was unit we went with at our dock mates suggestion. Very pleased. 

As ever,
Sean
Tenacious

Joseph Ruzzi

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Feb 1, 2026, 12:24:33 PMFeb 1
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Like Sean, I'm also in Annapolis.  To deal with summer heat, on our J/40, Spada my solution is use a "Portable A/C" unit that I strap on the cushion on the port side of the salon, just aft of the main bulkhead.   (It's the type of a/c unit that's often used to cool server rooms.)  I made a light plywood plate for the exhaust hose that fits into the opening port right above the a/c unit.   The unit blows cool air into the salon, with fans to push the air into the V-berth and the quarter-berth.   It's not perfect, but it does the job on blistering Chesapeake summer days when I can plug into shore power at a marina.

In actual usage, I'll set it up once we tie up at a marina.  Letting it run for a few hours while we're at the pool or having dinner will pull at least 10-15 degrees below ambient temperatures outside.   That makes it possible to sleep in relatively pleasant temps.   It worked well enough that my wife, who was going through chemo at the time making her extremely heat sensitive, was able to sleep on the boat.

I'm not sure if all of the portable a/c units work this way, but one benefit of this one is that the condensate is injected back into the exhaust stream, so there's no pan collecting water under the unit...that would inevitably spill onto the cushions.  I was dubious at first, but never found any water when I checked.

Mine was very similar to this model.  IIRC, 12,000 BU:
https://www.lowes.com/pd/DeLonghi-12-000-BTU-450-sq-ft-115-Volt-Portable-Air-Conditioner/50223305

Joe



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Dennis Boyd

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Feb 1, 2026, 1:21:21 PMFeb 1
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Guys, 

Thanks for the tips on cooling sheets and portable AC.    I know I will need something for a couple weeks this summer, and I really didn't like adding anything permanent.    Jaywalker is really a simple boat, almost still stock, which I like. 

Dennis
J/42 #6
Jaywalker

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