Generator size?

[SeaEric]

Does your boat's generator have the output capacity to run all of your Air units, the stove, refrigerator and the hot water heater all at the same time? Should that be expected? Would running 2 of the 3 Air units and the stove OR the hot water heater at once be a reasonable expectation?

Since I mostly don't run ANY air cond on the Gen, I'm thinking that feeding an 8kw may not be necessary when it can be replaced by a 6kw that will run cheaper and provide all the power that is needed 90% of the time.

I don't want to screw up the resale of the boat by installing what may be perceived as an "undersized" genset.

Your thoughts?

 

[MikeP]

The 16kw NL (replacing the oem 15KW Onan) on our 53MY will run all ac loads on the boat at the same time. I assumed that an oem genny on a boat would be expected to do that though I don't really know if that's true. That being said, even though I have tested our genny to ensure it would actually run everything - I can't think of any occasion when that would actually be necessary.

 

[CapetaniosG]

You don't say the size of boat you have but if I was you I would replace the generator with one comperable in size (KW) as the original furnished by the vessel manufacturer espessially if you're concerned about resale value. But it is your boat and can do whatever you wish.

CapetaniosG

 

[Brian Degulis]

Our boat has 7 AC units a 4500 W water heater electric stove etc. We have 2 20KW gen sets. It's a 61'MY and the second genset was optional some have only one. All of the AC loads would exceed 20KW by quite a bit so the OEM boat with one genset would not have enough capacity to run the whole boat. We have had the boat a while and even with every state room ocupied I've never had to run 2 gensets and I'm not running around with a calculater counting kilowats either. I just have to remember to shut off the water heater when we are using multiple burners and the stove.

Brian

 

[Fanfare]

If I had a boat for resale I'd go with the size of the original generator. But for a boat I would keep, I'd go for about 90% generator capacity. My 50MY came with 12 kw which ran everything. Then, with progress, I added an additional AC unit, larger water heater, self-cleaning oven and a watermaker. While I could get a generator big enough for all this, practically I would never run all at once. With my current 12.5 kw Phasor generator I can stall it with everything on, and I can trip my 50 amp shore connection circuit breaker. No point in rewiring when I can just manage the load by shutting something off.

It's also not a good idea to run a generator under light load for long periods. Our biggest load is air conditioning. We have done mostly spring cruising recently, and seldom have more than one or two units on at once.

I also suspect that smaller generators are more thrifty on fuel.

 

[REBrueckner]

Your should go with what meets your needs and style for the long term:But if you plan on possibly selling your boat in the near future, I'd be inclined to replace with the same size genny.

Look at it this way: if you normally use, say, 5KW, the difference in fuel use between a 6 and 8 KW unit will be miniscule...they are both powering for 5KW output and the only time the 8KW unit would use more fuel is when it's pumping out 7 or 8 KW...You'd be hard pressed to show any real savings in fuel costs....

 

[Genesis]

My expectation is that I should be able to run all normal cabin loads at the same time, which I define as the hot water heater(s), AC units, and at least ordinary galley appliances (e.g. microwave)

I am willing to shut down a stateroom AC to use an oven or multiple burners on the stove.

This, by the way, is how the 8kw on Gigabite, which was "as delivered", worked out. I would not have installed something smaller, and something bigger would not have been adequately loaded during "lighter" need times.

 

[captbuddy]

During the sea trial of Beach nut several years ago my buddy turned on everything on the boat at the same time. The owner stated he thought that was to much to have on at the asme time. My buddy told him we wanted to see if the 7.5 would pull all 3 AC's and the stove and Microwave. It grunted but it pulled it with no problem. Would not go lower. Would stay with what Hatteras put in. Especially after this weekend at the Expo. Hatteras knows what they are doing.
captbuddy

 

[Genesis]

Yeah, on Gig it came with an 8kw and I could pop the breaker on it, but I had to work at it. The 900lb Gorilla that would do it was to fire up the 3-burner stove and oven with all three ACs and the water heater going.

That was a few too many amps

 

[Fanfare]

Here at home I have a little 2 kw emergency gasoline generator. Every year or so I test it by filling its little gas tank and then running it until empty. That way there is no residual gas left to go bad. I think it runs at 3600 rpm. Some years I just let it run by itself, others I connect an electric heater and a few lights to run it at its full output. Strangely, it seems to take about the same time to use its tank of fuel, about 2.5 hours, whether loaded or not. So apparently the friction of merely turning 3600 rpm is equivalent to the 2 kw load. It is a simple Briggs and Stratton air cooled, splash lubricated engine. But I wonder how this holds for our larger diesel generators. I don't think I have any info on gallons per hour at load.

 

[MikeP]

Our 16KW NL M844k genny burns one gallon of fuel in 64 minutes while heavily loaded. I tested this three times using a graduated beaker to measure the fuel used.

 

[ThirdHatt]

Our 16KW NL M844k genny burns one gallon of fuel in 64 minutes while heavily loaded. I tested this three times using a graduated beaker to measure the fuel used.

That sounds about as accurate as you can get! I'd rather believe you anyway because I thought the manual for the M844K shows 1.5gal/hr fully loaded. Both of these figures are from the manufacturers, and I have not tested them in the real world as Mike has.

The boat also has a Westerbeke 7.6KW genset that I use 80-90% of the time because it only burns .5 gal/hr and is half the cost to replace! It runs 3 A/Cs and everything else (in moderation). It will carry all 4 A/C's but not much more.

Keeping the little one heavily loaded seems the way to get great life out of it and I use the 16kw for heavy loads occasionally, keeping hours down on it and saving fuel.

I would agree that near the factory size should be the wise choice for a replacement, but just run those A/C's all the time. I have even run one on heat and one on A/C at the same time in the salon in an attempt to keep a load on the 16kw. You start to wonder what is worse, wear and tear on your a/c's plus the extra fuel used to run them or the damage that light loads do to the genset. Tough call!

 

[krush]

The generators in construction site light towers only run about 50-75% load for long life. I don't think running 100% load increases life on anything.....

 

[Pascal]

i really woudln't undersize a genny, it shoudl be able to run jsut about everything... AC, water heater, lights and TVs, charger, and a couple of appliances... all 4 burners at once? nope, how oven do you cook with 4 burners anyway. but a burner or two and the over, yes.

you're not going to save any fuel by installing a smaller unit. a 15kw genny producing 8kw is going to use roughly the same amount of fuel as a 9 kw producing the same 8kw...

it will be a little cheaper to buy a smaller one but it could affect resale.

on a boat with dual genny, you should be able to run everthing off one. 6 or 7 ACs, chargers, water heaters, stove, etc... should be no problem with an 18 or 20kw unit.

 

[dwaynec]

Something I have always wondered about. Since our boats have 50 amp service whether on shore power or on the genny, why would we need more than a 12.5K genny? Anything greater than that would mean that the genny would never be fully loaded. Correct?? With our current 15K genny it should be able to put our 60 amps at 250 volts but the breakers will trip before it gets there.

Am I missing something?

 

[34Hatt]

Something I have always wondered about. Since our boats have 50 amp service whether on shore power or on the genny, why would we need more than a 12.5K genny? Anything greater than that would mean that the genny would never be fully loaded. Correct?? With our current 15K genny it should be able to put our 60 amps at 250 volts but the breakers will trip before it gets there.

Am I missing something?

NOPE!!!

I see that Seaeric still has not said what size boat this is for??

I have that exact problem also 8K unit can put out almost 70 amps 120V my panel has two 30 amp main's and I already upgraded it from Hatteras OEM. I go to a dock and get 50 amps!!! Which still has plenty so it all depends on the boat and I have 2 ac units which most 34' have only one.

I would have put in a 5-6K unit but the 8K was a good deal

 

[Pascal]

"Something I have always wondered about. Since our boats have 50 amp service whether on shore power or on the genny, why would we need more than a 12.5K genny? Anything greater than that would mean that the genny would never be fully loaded. Correct?? With our current 15K genny it should be able to put our 60 amps at 250 volts but the breakers will trip before it gets there."

Well, that's what i had been thinking for a while.. BUT... what about the 220v circuit? it's not on the same breakers.

So, i get 50amp to each leg PLUS another 50amp to the 220V subpanel for the stove. So in theory i can actaully use the full genny capacity.

took me a while to figure that one out

 

[dwaynec]

Your boat must be setup differently than ours. Both the 125V lines run off the 240V line so the max we can use is 50 amps when on the genny. When hooked up to shore power, we can hook up to 50/125 lines and a 50/250 line, but on the hook it is strictly 50A 250.

Might have to buy a bigger boat for my genny. LOL

 

[MikeP]

A 50 amp service from shore will not come close to running everything on our 53MY. If BOTH 50 A inputs were connected then it might but I have never been in a slip sized for our boat that had 2 50A shorepower connections - and I wouldn't bother hooking both up anyway.

I assume all these boats are set up the same way - we have a shore power/generator panel that allows you to select shorepower 1, shorepower 2, and/or the genny for each of the 3 master subpanels. So in theory, you could have panel 1 from shorepower 1, Panel 2 from shorepower 2 and Panel 3 from the genny. There's no reason you would ever want to do that but each panel, which feeds different circuits can be individually switched to accept power from whatever source. Normally, they are all switched to whatever shorepower source the cord is plugged into or the genny.

Here's a pic of the panel. When we picked up the boat and sailed it home, it took us a couple of days to figure it out!

 

[nyrussell]

Nope on the Panel setup. I have just one selector Here.