May 22, 2016

Air Conditioning? [Living on a boat in hot weather...]

We occasionally participate in various boating forums. [See our Some Forums We Read sidebar for links...]

Some of those topics may be relevant here, so sometimes we repost to our blog for reference.

The following may be one of those cases. To accommodate our non-boating blog readers, add additional detail, and/or just cause more confusion, I sometimes add some additional {information and links} to the original forum post, below.

Related Posts:

Link to original forum post [28-Dec-2015]

Re: Novice air conditioning question

Originally Posted by pwilletts View Post
it seems we cannot live w/o air conditioning...I see that a lot of boats have it but not many have a genset to run it offshore.. would prefer not to use the Honda solution...what type of electrical set up will power AC w/o a genset..I assume it involves a big alternator/ big inverter and isolated switching??

From your phrasing, I'm assuming shore power is not regularly available to you in your current boating lifestyle. Therefore I suspect you would need a generator if you don't want to prematurely wear out your primary engine charging batteries. [Unless you are motoring most of the time anyway...]

But I say this based upon how our boat is set up- which I'll share here for perspective on a thoroughly tested and proven setup:

The previous owners used our boat in the tropics for 15 years and therefore installed 3 independently controlled and regulated air conditioners [A/C: 9k BTU fore cabin, 18k BTU pilothouse, and 18k BTU in the master cabin. All are raw water cooled using a single pump and plumbing circuit.]

Since the A/C units each have a dedicated circuit breaker and thermostat, we can run 1, 2, or all 3 as needed. [Note: when at the dock in winter we use them for heat since our current hydro electric power rates are cheaper than putting hours on our generator or Esbar diesel heater...]

Using shore power, running all 3 A/C units requires a 50 amp [or two properly paralleled 30AMP services] 115VAC [split 230VAC feed] to handle the A/C load as well as the normal boat loads [water heater, battery charger, etc.] A 6.5kw generator would also handle them and the boat, but we have a 10kw generator instead. [We were told it cost the same as the 6.5 at the time the previous owner's installed it...]

Back to your question: Could we run one of these A/C units at a time from our 2800 Watt 115VAC/125A 12VDC inverter charger? Yes. [On paper anyway- I have never had the need to attempt it...] Our 900 AH 12VDC house bank would likely handle it for a few hours. However, the energy/time required to recharge the batteries outweighs the benefits for me. Therefore we choose to run the generator when away from shore power when A/C is needed, and let it take care of other needs during that run period. [Charge batts, etc.]

Even though the need for A/C is rare where we currently cruise [55N-61N] occasionally we do exercising the units on those hot days when the pilothouse [AKA solarium] starts climbing through the mid-90°s F due to the sun. [Even with all hatches open and fans running- including a hatch exhaust fan...]

Running the A/C is also great for quickly drying out [dehumidifying] the boat when needed... [We use our dehumidifier to dry the boat as needed when A/C is not really necessary...]

I don't mind running our generator as it is very quiet and surprisingly fuel efficient. [Fisher-Panda running a 3 cyl Kubota diesel.] Yes, we can hear the low hum of the generator in the pilot house, but the blower from the AC on high drowns that out.

And outside our split exhaust arrangement makes it difficult to tell if it is running unless you wander over to the exhaust area and lean over to hear it blowing bubbles...

Any neighbors would never know it was running... but neighbors are rare for us... We have had kayakers approach and not realize they were approaching the running gen exhaust until they were within ~10 feet of the boat...

I hope this helps provide some prospective from another vessel's point of view.




  1. I've never considered putting ac on our boat, but then, I haven't yet spent a season in Mexico! I'm not going to say 'never'.

    1. I know what you mean... A/C is a big expense when you include the auxiliary systems also necessary...

      If this boat hadn't come with A/C already installed, adding it would not be on my list of projects unless we were planning to head for the tropics [Of the two of us, I'm the only one who has cruised there...]

      Of course, our A/C is also a good heat source when we are at the dock in cold weather...

      All this time spent at higher latitudes has 'thickened our blood' to the point where we no longer tolerate heat well. [Heat defined as >80°F for me...]

      The last time I flew to Puerto Vallarta in Oct-Nov timeframe a few years ago to help some long time cruising friends make a passage, I was a safety hazard on the boat for the first week because I never, ever, stopped sweating [and heat was the only causal factor for the diaphoresis...]

      Water pooled around me, and swimming in the tepid ocean didn't cool me down enough; cold showers helped...

      That experience cemented A/C on our requirements list IF we ever decide to spend time in tropical climes again... It has been escalated from luxury to quality of life...

      Everyone is different, and A/C is certainly a luxury to be enjoyed only when needed for us. [Our 3 units are independent, so we could just cool our sleeping cabin/ main cabin/ fore cabin as needed/desired...]

      One reason for this post was to also point out some of the A/C installation design considerations that are somewhat different on our boat- for others to possibly benefit from if they decide to install A/C.

  2. Very interesting post. I didn't know much about A/C installation or set-ups before I read this. We currently have a window unit plugged into shore power and I know I'm going to miss it terribly once we get off the dock :-)


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