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Old 08-06-2013, 09:38 AM   #1
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Generator KW required

We have been looking at trawlers as our next boat for long range cruising. We have pretty much settled on the 44 Defever as the one we want. I have found one that is a 2001 but it only has an 8 KW on it. I currently have a 10 on a smaller boat. I am thinking a 44 would be more suited with a 12 kw. Question is, is the 8 enough or would power management become a full time job?
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Old 08-06-2013, 09:43 AM   #2
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Does the boat have any gas appliances? If it was bult with a 8kw and all that does is run water pumps, ac's and lights than that would be enough. If it has to run a electric oven/range/fridge/heater.ect than it would probably not be enough.
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Old 08-06-2013, 09:54 AM   #3
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An 8 kw will run a lot of stuff. If you have 3 A/Cs and electric cooking, you could have to do a little load management. I would look into adding a 3.5 to 5kw generator to bring on line when needed. Also, if doing island cruising it could serve as backup if the big one goes down. Battery charging and refrigeration are the essentials. A spare battery charger and/or inverter are also good ideas. Don't ask me how I know.

Plus you would have to be careful to keep about a 70% load on a 12kw. Much easier on an 8.
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Old 08-06-2013, 09:57 AM   #4
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Total everything up on the boat you have now. How many amps full on? What does the 44 have over your current boat that would take an additional 3-3.5KW?

We have an 8KW now and we don't load it correctly. Our 2-16KW ACs draw 19 amps, add the charger, hot-water heater and we're less than 50 amps total. Add a toaster or microwave we're getting close, but only for a few minutes. We cook with propane.
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Old 08-06-2013, 10:14 AM   #5
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A 8 KW# will produce 60 amps (8,000/120). Most boats are wired for 50 amps, so the 8 KW is sized the boat. The Eagle is wired for 50 amps, so what we did was load share, put timers on high demand items and convert things to DC, propane and diesel to reduce the total amp draw.
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Old 08-06-2013, 10:24 AM   #6
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We have a 47' boat with all electric appliances including a clothes washer.

Since we are in the PACNW we do not have AC though.

We're running a 9 kw generator and never have to power manage.

consider this...

A 30 amp 120 volt dock connection is only 3.6KW

A 50 amp 120 volt dock connection is only 6KW
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Old 08-06-2013, 11:06 AM   #7
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Thank you all for he insight. I think we will go look at the 44 we found. We locked through this weekend next to a 44. They docked next to us and we got to meet them and see the boat. Great people and a really nice 44, she was a 1990.
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Old 08-06-2013, 11:08 AM   #8
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Most boats have a generator that is too big to keep loaded properly.

If you just add up all of your AC loads and size your generator accordingly you will have a tough time keeping that generator loaded to 25% and at night when the A/C load drops off, it may be as low as 10%. That won't be very good for the genset's engine.

So size your generator to run those loads that absolutely have to run simultaneously and do some power management to keep it loaded like don't run the microwave and the hot water heater at the same time, etc.

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Old 08-06-2013, 11:41 AM   #9
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8kw should be just fine!!!
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Old 08-06-2013, 11:43 AM   #10
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8kw should be just fine!!
Couldn't agree more! You always have a management situation aboard, relative to your electrical needs, and if you don't, you have too big a boat!
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Old 08-06-2013, 11:44 AM   #11
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If you find that the genset is a little small for peak loads (eg running multiple air-con units simultaneously) you might find the best strategy is to invest in a load-sharing inverter/charger of the type made by Victron and MasterVolt. These are capable of adding to genset capacity for peak/surge loads & allow for a smaller genset to do the job. Also means the smaller genset is running better-loaded most of the time...as noted above by others, this is a good thing in its own right.
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Old 08-06-2013, 07:13 PM   #12
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If you find that the genset is a little small for peak loads (eg running multiple air-con units simultaneously) you might find the best strategy is to invest in a load-sharing inverter/charger of the type made by Victron and MasterVolt. These are capable of adding to genset capacity for peak/surge loads & allow for a smaller genset to do the job. Also means the smaller genset is running better-loaded most of the time...as noted above by others, this is a good thing in its own right.
I could not agree more. I have a 6KW and I run it through a Xantrex 4024MC, which has load sharing. It works like a charm.

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Old 08-06-2013, 09:42 PM   #13
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wow...what understatements...8kw isn't nearly enough if you need it and WAYYYY too much if you don't.

People in this forum thought I was crazy for upgrading 2-30 amp services to a 50 amp 120/240 which produces 12,000 watts or 12 KW...and living aboard you can easily exceed that amount like the average house nowadays needs more than a 100 amp service.

Until you know what kind of "hotel services" you will be demanding at anchor or at no electric docks...you have no idea what king of genset you really need. Many boats with propane cooking can get by with a very small genset...mainly to heat water and run the batt charger. But if you like all electric (cooking included) and run a space heater or two during chilly weather...8KW is gonna run out fast.

The real trick is to find out what you need MOST of the time and size the genset to that. If you need more...maybe augment with an inverter or switch some appliances to other energy sources.

You don't want too big or too small..and what are your other options...

Kinda difficult to answer in a forum paragraph or two.
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Old 08-06-2013, 11:50 PM   #14
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Also note what the wiring in the boat will handle. If it comes with an 8KW and you want to upsize to 12, you may need to rewire to handle the extra amperage. Now THAT is a big job.
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Old 08-07-2013, 09:41 AM   #15
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MY boat is 46' and we have a 7 KVA genset. By the way, we are in a tropical country where AC is paramount. We have total 24000 BTU in the boat, MW, charger, one domestic refrigerator and several lamps.
No need for bigger genset
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Old 08-07-2013, 12:40 PM   #16
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MY boat is 46' and we have a 7 KVA genset. By the way, we are in a tropical country where AC is paramount. We have total 24000 BTU in the boat, MW, charger, one domestic refrigerator and several lamps.
No need for bigger genset
Wow...good deal on the Air Conditoning...

I'm in a relatively cool zone with 32000 BTUs of Air Conditioning on a relatively small 40 footer.

Either way I'm still only at 30 amps for the a ACs and would have enough (either with my 8kw or your 7kw) to run enough other stuff...especially with a propane range.

Most of the time at anchor...unless cooking , running electric heat or air conditioning....much above 5kw is hard to really work hard enough for it to be good for the genset.
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Old 08-08-2013, 05:31 AM   #17
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Question is, is the 8 enough or would power management become a full time job?

8KW is plenty , and at a very modest cost automatic LOAD SHEDDING is easy to install.

Once worked out life is very simple
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Old 08-08-2013, 06:11 AM   #18
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...and at a very modest cost automatic LOAD SHEDDING is easy to install.
I looked at this for my house genset once. The theory is very simple, and I'm sure it's easy to install. I'd like to hear more about the "very modest cost" part. As I recall, that's not what I found.
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Old 08-08-2013, 09:32 AM   #19
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Question is, is the 8 enough or would power management become a full time job?

8KW is plenty , and at a very modest cost automatic LOAD SHEDDING is easy to install.

Once worked out life is very simple
Actually I'm in the wholesale power switching business and I have not and cannot find a commercially available automatic load shedding device.

The units that are being deployed are one off devices built from a protective relay and contactors by the electrician. Nobody is happy with this but again nothing is available that works.

There are a couple of units that work in their specific brands of generators, but nobody elses, but there is nothing that I can find that does not utilize propritary signaling.

The concept is simple, but there is nothing is commercially available yet.
If you know of somethingthat is available, and is UL listed, please either post it or PM me, because I can and will add it to our product portfolio.
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Old 08-08-2013, 09:41 AM   #20
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Also note what the wiring in the boat will handle. If it comes with an 8KW and you want to upsize to 12, you may need to rewire to handle the extra amperage. Now THAT is a big job.
Unless you increase the consumers (load) you can put a 500kW generator in and not have any problems with the wiring.

Amperage is not pushed down the wires, it is dragged.

With regard to load shedding, I have never used one of their products but Panbo makes a programmable load shedding controller for small boats that might serve the purpose very well.
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