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Old 20-01-2013, 01:38   #1
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Generator Diesel Usage

Me and my wife both have COPD (Chronic Obstructive Pulmonary Disease) aka Emphysema. Neither of us are on oxygen but out life style have been forced to be slower due to breathlessness. We would like to do the Great Loop and take 18 - 20 months to do so (making stops in the Bahamas, Cuba and to Cancun Mexico to see the Mayan ruins and finally taking the long way around the gulf of Mexico, North thru the ICW finally to cross our wake on Lake Ontario.

Now with our COPD; the heat and humidity CAN bother our lungs and therefore; would require the AC to be running more than most people would require air conditioning. My question is; is there a way (a formula) to estimate the amount of diesel used based on the AC draw (amperage) of the air conditioning unit and other running equipment used while on the hook?

With some luck; we would like to get a Great Harbour N37 which comes standard with a 8kw Maspower (Yanmar) Genset.

Any advice on this?
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Old 20-01-2013, 01:53   #2
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re: Generator Diesel Usage

I'm guessing you are US based so I'll give burn rates in gallons per hp. 0.4 lb per hp, so an A/C pulling 1500 watts would be 0.144 gallons per hour, less if the A/C cycles to hold your desired temp.

For other calculations just remember

0.4 lb of diesel per hp.
1 gallon of diesel is 7.49 lbs
746 watts = 1 hp
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Old 20-01-2013, 03:08   #3
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re: Generator Diesel Usage

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Originally Posted by deckofficer View Post
I'm guessing you are US based so I'll give burn rates in gallons per hp. 0.4 lb per hp, so an A/C pulling 1500 watts would be 0.144 gallons per hour, less if the A/C cycles to hold your desired temp.

For other calculations just remember

0.4 lb of diesel per hp.
1 gallon of diesel is 7.49 lbs
746 watts = 1 hp
You're assuming 100% efficiency of conversion of mechanical energy to electrical! Sorry, but it doesn't work like that.

Most gensets will give you a table for fuel consumption at 25%, 50%, 75%, and 100% load. If you know power draw of your AC, you can work it out from hat. Hard to predict duty cycle of the AC, however.

If I were you, I wouldn't worry too much about. Fuel burn for AC will be a minor factor compared to main engines in a trawler covering so many miles.
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Old 20-01-2013, 03:14   #4
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Re: Generator deisel usage

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Originally Posted by deckofficer View Post
I'm guessing you are US based so I'll give burn rates in gallons per hp. 0.4 lb per hp, so an A/C pulling 1500 watts would be 0.144 gallons per hour, less if the A/C cycles to hold your desired temp.

For other calculations just remember

0.4 lb of diesel per hp.
1 gallon of diesel is 7.49 lbs
746 watts = 1 hp
Now you have to factor in that an AC generator has to run at a fixed speed no matter the load. An AC generator has to be sized to the maximum starting load. Not the actual running load.

So at night when all are asleep and only the air-con is running the generator will be running well outside it's maximum efficiency.

Not to mention that diesel exhaust is probably one of the the worst triggers of COPD attacks. Now factor in that the diesel gen-set is running at the worst burn rate, and it's particulate exhaust will be at it's worst.

Lloyd
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Old 20-01-2013, 06:45   #5
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Re: Generator Diesel Usage

The previous poster's comments about efficiency are correct. Mastervolt published an article where they evaluated several genset's efficiency at low load. They were all terrible.

Mastervolt was promoting theit "hybrid" system, which is an integrated diesel generator and inverter/charger. Unfortunately it is only available at 230V/50 Hz.

But you can make your own. Buy a 5 KW three cylinder, low speed genset like the Northern Lights. The 8 KW Maspower will be less efficient at under 5KW. Hook it up to a Victron inverter/charger.The Victron and some others have a feature that lets the inverter pick up the load from a genset for peak motor starting currents. That lets you run a small genset at high loads for best efficiency. You can also wire it to automatically start the genset when the batteries get low.

If you try simply to run your genset 24/7 without an inverter you will burn a lot of fuel and you will wear out the genset because they don't like the light load that you will be using at night.

And set up your boat's A/C with a small unit, perhaps 6,000 btu in your sleeping cabin and a bigger one in the main cabin. That way with a decent size battery bank the small one can run all night on just batteries and inverter power. Then in the morning when it starts to get warm, start the genset to recharge your batteries and turn on the main cabin's A/C.

But even with a sophisticated genset/inverter/battery system and judicious management of genset running time and load you are probably going to burn 5-7 gallons of diesel in the genset in 24 hours.

And by the way, do you have the seamanship skills necessary to cross the Gulf of Mexico, although the N37 does have the range? I would think seriously about flying to Cancun rather than trying to cruise there on my own boat.

David
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Old 20-01-2013, 07:40   #6
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Re: Generator Diesel Usage

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And by the way, do you have the seamanship skills necessary to cross the Gulf of Mexico, although the N37 does have the range? I would think seriously about flying to Cancun rather than trying to cruise there on my own boat.

David
Actually We would (hopefully) enter Cancun from the western tip of of Cuba. From there we would NOT be crossing the Gulf but making little hops south and west to Marida, Campeche, Veracruz, Tampico and so on finally entering the US again in the area of Corpus Christi. Crossing the gulf from Cancun to Mobile would be suicide and even though I am a risk taker not even I am that adventurous...lol. The trip AROUND the gulf would likely take about 4+ weeks.

The reason we would want to do that is so we were not entering the US again from Cuba. The only other option would be to back track back to the Bahamas and then enter the US from there. My only concern (about hoping westward along the coast of Mexico would be the safety issue (after all outside the tourist areas, Mexico is not the most hospitable place for foreigners - or so I've heard.

And thanks to all for you genset answers I now have a starting point and some numbers to work with.

Finally @ FlyingCloud as or the diesel particulate I would have the main engines and genset fitted with a Diesel Particulate Filter (DPF) which would eliminate 90% of any exhaust particles.

Thank you all; I am impressed with the responses and the high quality of knowledge in this community.
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Old 20-01-2013, 08:28   #7
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Re: Generator Diesel Usage

Nice boat you have, by the way

I'm a sailor, with no plans to ever go over to power, but . . .

Your boat has the design features I would look for in a trawler if I were in the market for one -- twin engines, twin keels for drying out, very efficient hull . . . very salty!

I might put on feathering props (best of all self-pitching) so I could motor on one engine at a time on long passages, the way catamaran drivers do under power . . .
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Old 20-01-2013, 08:39   #8
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Re: Generator Diesel Usage

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Originally Posted by Dockhead View Post
Nice boat you have, by the way

I'm a sailor, with no plans to ever go over to power, but . . .

Your boat has the design features I would look for in a trawler if I were in the market for one -- twin engines, twin keels for drying out, very efficient hull . . . very salty!

I might put on feathering props (best of all self-pitching) so I could motor on one engine at a time on long passages, the way catamaran drivers do under power . . .
Actually I don't have it yet... I'll soon be in the market and the N37 is my ideal vessel (they are hard to find) but would settle for something similar. For me ideal would be dual screws, 32 - 38 foot, top speed in the 12 - 16 knot range and full displacement with a 4 foot draft or less.
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Old 20-01-2013, 09:11   #9
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Re: Generator Diesel Usage

We have a Panda 4.2KW generator pushing a 16K BTU reverse cycle AC unit. Other than the start-up loading, the demands on the generator from this unit are quite low and we need to "add load", usually the hot water heater and battery charger, to keep the generator operating in its most efficient load range. With that our fuel consumption is about .3 liters per KW hour or .2 gals/hour. On AC only, that falls to about .15-.2 liters.
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Old 21-01-2013, 19:44   #10
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Re: Generator Diesel Usage

Our 8KW drinks 1/3 to 1/2 gallon per hour, depending upon load. Typically that's 12,000 and 16,000 BTU A/C units.
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