Lets Talk Air Conditioning - Size Matters

[cat man do]

Originally Posted by Pblais

We had a 33 ft boat with 12,000 and it was not enough. Our current boat is 36 and 16,000 is about right.

Interesting comment

I have been on this vessel on a 35c 95f day and its 9000 btu split system a/c worked quite well with a 2 kva Honda EU20i.

I would have thought it had more room than a 36 ft Mono

[sailguy23]

I know this is a old thread, but somebody may get some use of my 1st hand knowledge.

To get to the point, we have had A LOT of success with a single Honda 2000 running a 16,000 BTU marine air.

Our boat is a 44ft sailboat, Brewer 44, and we live full time in Miami, FL. We live at anchor and therefore need air conditioning for the summer to run of generators. The boat currently has one 16,000 btu in the mainsalon/v-birth and a 12,000 btu in the aft. The boats inboard 5kw diesel generator runs both ok, but we prefer to use the Honda 2000 to run the 16,000 BTU air and sleep in the v-birth.

I have talked with a lot of air-con manufactures that say that a honda 2000 will not start an a/c of that size, and they recommend a "smart start" or "easy-start" to run that load and some say I need to use a smaller air con/bigger gen.

Lets talk numbers. The Honda 2000 is rated at 1600 continuous watts, or 2000 peak watts for 30 min or less. Our forward 16,000 BTU air con draws 12.7 amps when running the compressor, fan, and raw-water pump. My honda puts out 122 volts when running and so when it is running, I am drawing 1550 watts. I have checked this at the generator outlet with a very accurate klein tools cl200 clamp on multi-meter, which has a 3% current and 1% voltage accuracy.

So, what about start-up current? How do I kick off the compressor with the little honda? I follow these steps:

1) make sure all other 120 v loads are off
2) turn off eco-throttle on honda (increases rpms to allow larger shock load)
3)turn air to "start" which turns on fan and raw water. this equalizes the air con with surrounding conditions, and makes it easier for compressor to start I have found
4)just turn on air conditioning to run and make sure compressor starts.

When I follow this sequence, I have NEVER had the honda not start the air conditioning compressor. The only times I have had it not start was when I skipped these steps and had the generator on eco-throttle (although I have had success running starting it from the eco-throttle setting as well).

Now, dont get me wrong, the compressor struggles a bit and the honda really comes to life to get the compressor running, but it seems VERY happy running it after it is started. It absolutely works as well as when connected to shore power, and even better than the inboard diesel that produces 115v and 59-61 hz power.

People have mentioned damage of the compressor cycling on and off with insufficient power. I think this is true and a concern, so I turn the a/c thermostat all the way to cold, to ensure it will run continuously all night without cycling. As we run this in the miami summer, it needs to run continuously anyway to keep everything cool. If we are too cold, we will crack a hatch, but hardly have to do this.

The last two factors are cost/fuel and noise.

Fuel consumption for the honda, when fully loaded such as running air, is 0.23 gallons per hour. In other words, 1 gallon lasts 4hrs and 15 mins. I modified my fuel cap to run it to an external fuel tank. Obviously, for 8 hrs sleep, it is just about 2 gallons of gas. It usually comes to about 10 hrs per day, so 2.5 gallons per night, so a 6 gallon fuel tank comes to a bit over a couple nights of air conditioned comfort aboard the boat.

I have estimated the cost to run the inboard genset at 75 cents/hr and the cost of the Honda at about 40 cents/hr (this estimate comes from estimate of engine life and average cost of engine maintenance and oil changes). (google steve dashew engine cost to read more about estimating engine cost per operating hour).


Each night then, cost of fuel and engine run cost, I am about 10-11 dollars per night. The cost of the marina, even at yearly low rate, is $30 per night, so I am 1/3 the cost, even during the summer with extensive a/c use.

Finally, the noise. Honda's are quiet. Remarkably quiet. Hondas vary their rpm based on the load, so when there is a little load, they run very quiet. The a/c maxes the honda out, so it is considerably louder. To keep me happy, I use my solid wood companionway hatch sliders to keep the sound outside. When placed in the cockpit, despite being 10 ft away from my head when I am in the galley, is quieter that the inboard diesel. I can definitely still hear it, but it is not that loud. When sleeping in the v-birth, the a/c almost quells the generator, and is barely audible. (Sorry I have no quantitative comparison for this aspect)

For neighbor comfort, I remain cognizant of noise created and place the generator according to neighbor location and wind direction. I have found that the cockpit coaming works well to direct the sound within the boat and the noise travels less over the water. I direct the engine exhaust away from my closest neighbor. At 2 boat lengths away, the sound is not offensive (I have heard from my neighbors).

**as a note: I am guessing that the honda will have about 3000 hrs of engine life. To increase the engine longevity, I change the oil once a week in the summer. There is no oil filter and so the oil is the only way to contain the internal contaminants. The engine holds less than a half a quart of oil, so there is practically no cost benefit of having a longer oil-change interval.

My Honda has close to 1000 hrs on it now, and appears to run flawless thus far.

Originally Posted by Pblais

We had a 33 ft boat with 12,000 and it was not enough. Our current boat is 36 and 16,000 is about right.



Not even enough to be close. What a Honda 2000 will put out (nice generator BTW) won't start any AC you can install and be cool. At 4000 you might get close, but it won't do 16,000 btu's in your dreams. I doubt two would do it either. The starting amps required on an A/C is more than these will sustain. Under voltage would trash them given the loss to the Inverter required to power them. They really want AC voltage. At three you might be in the ball park. There you ultimately die since the fuel tanks are too small and the noise times three is worse.

The concept of A/C on the hook is false unless you have the serious genset. You then pay the price of the purr of a diesel engine. Silence in heat is better or find a higher lattitude. Running a genset all night is not occasional use. The Hondas barely make it recharging batteries. They work well for the time you need them and then shutting them off. If all this worked no one would own a real generator.

[valhalla360]

We have a Yamaha 2400 running a 12k btu unit. It's just about right and doesn't sacrifice the eco mode. Dropping much below this and it seems to be a crap shoot depending on how hard it is to get your compressor to turn over.


The one downside is you can't use the simple suction auxiliary fuel tank, so we only get around 6-8hrs run time running the air/con.