What size Generator?

[mcgann454]

I need to install a new generator.
The boat will be used for the loop.
The old generator was a Westerbeke 8KW 8BTD.
I have a 1984 Heritage East Nova Sundeck.
I have changed all of the lighting to LED and understand that does not have too much effect on he total needed.
I did add a second 18K btu air conditioner and have studied all of the threads on generators but would like a second opinion as I am unclear on what I should have so I have reserve wattage, but don’t under load the generator.
I also have a Victron multiplus with the spike protection that draws from the batteries for start up spikes if needed. I can’t find a start up amp spec for the air conditioners
Here is what I believe I would have on the hook cooking dinner in the Keys:
2) Dometic 18Kbtu air conditioners at 15.1 amps(15.1x120x2) 3624 Watts
Not sure of the draw for the two water pumps 370 Watts?
Norcold 6 cu/ft AC/DC FRIDGE/freezer .4 amps (.4x 120) 48 Watts
Two burner electric stove top 1200 Watts
Oven 1200 Watts
1200 watt microwave
20 Gal electric water heater 2000 watt
Tv and sound bar
Uline ice maker
If I add up all of the major appliances outside of the TV and Icemaker it totals to
9642 Watts.
Add the Charges/Inverter is another 15 watts?
I realize they might not all be on at the same time and I should turn some off if using others. I also read that a generator should be loaded between 30 and 70%.
I do have 6 100 watt solar panels I will be installing this year as well.
If I get a 9KW generator, I could potentially load it to 100%.
Does an 11 KW generator make sense?
Thanks in advance.

 

[dhays]

The loop sounds great. Only you know about your typical usage.

I’m cheap so I wouldn’t spend more than I needed. If it was me, I wouldn’t be running all those applicants at the same time. In other words, the way my wife and I cook we wouldn’t be using the oven, both burners, and the microwave at the same time. I’m also used to managing power and it doesn’t bother me. For example, if you have been running the boat and have anchored, you will have plenty of hot water for cooking from the engine (assuming your hot water tank has a heat exchanger from your engine coolant). So your hot water tank can be turned off when you are cooking. Likewise, you can turn your fridge to DC so that your batteries can handle the fridge while you are doing everything else. That is assuming you have your AC running as well.

Some folks really don’t like to have to manage power and some folks are incredible cooks who would use all cooking appliances at once. If that is your situation, then go with the larger genset. Otherwise, I think 9KW would likely be fine.

 

[The Other Gary]

8 or 9 KW because you will never load it 100% and your normal loading should be in the upper half of the range for the genny's

 

[ranger58sb]

Add the Charges/Inverter is another 15 watts?
I realize they might not all be on at the same time and I should turn some off if using others. I also read that a generator should be loaded between 30 and 70%.
I do have 6 100 watt solar panels I will be installing this year as well.
If I get a 9KW generator, I could potentially load it to 100%.
Does an 11 KW generator make sense?
Thanks in advance.

FWIW, we have an 8kW genset, and it runs everything all at once: two fridges, two 16K BTU ACs, water heater, electric cooktop, microwave/convection combo, coffee maker, toaster, inverter/charger, other charger, etc...

-Chris

 

[DavidM]

You could get by with as little as 5 KW if you managed your power very carefully, particularly with the inverter helping on motor starts. But you would have to shut down one A/C for dinner prep and for heating water for showers at night.

Also your estimate of the charger load is very low. A 100 amp charger will draw 15A A/C but only when the batteries are low and not for very long.

7.5-8KW would be more comfortable. I wouldn't go to 10+.

David

 

[mcgann454]

You could get by with as little as 5 KW if you managed your power very carefully, particularly with the inverter helping on motor starts. But you would have to shut down one A/C for dinner prep and for heating water for showers at night.

Also your estimate of the charger load is very low. A 100 amp charger will draw 15A A/C but only when the batteries are low and not for very long.

7.5-8KW would be more comfortable. I wouldn't go to 10+.

David

Thanks all,
I was adding up to 11KW + and my options were 7.5KW or 9KW.
I think I'll go 9KW and call it good.
Thanks for the feedback.

 

[High Wire]

Question. Does the water heater have a engine heat coil? If so, you could easily get by with a 6.0 to 7.0 Kw unit with a little load management. For example if you are going to cook, turn off one Air Con unit and you are good. I have an 8 Kw and can only reach full load for about an hour before everything starts cycling off and I'm down below 2Kw.
We never use the air when anchored out except as a "dummy" load when battery charging. Maybe we are the exception.
So my advice is to look really hard at your load list and be realistic about what will be the most load that will always run concurrently for more than an hour.

 

[mcgann454]

Question. Does the water heater have a engine heat coil? If so, you could easily get by with a 6.0 to 7.0 Kw unit with a little load management. For example if you are going to cook, turn off one Air Con unit and you are good. I have an 8 Kw and can only reach full load for about an hour before everything starts cycling off and I'm down below 2Kw.
We never use the air when anchored out except as a "dummy" load when battery charging. Maybe we are the exception.
So my advice is to look really hard at your load list and be realistic about what will be the most load that will always run concurrently for more than an hour.

No, I cheaped out and installed one that does not have the coil for the engine coolant.
I did forget about the Admiral's hair dryer, curling iron and straightner, though, so maybe more is better.

 

[High Wire]

No, I cheaped out and installed one that does not have the coil for the engine coolant.
I did forget about the Admiral's hair dryer, curling iron and straightner, though, so maybe more is better.

No problem. The water heater only takes about an hour to heat up. Again, turning off one AC unit while cooking or other high load stuff and you can go much smaller.
Just curious, how did your 8BTD die? Mine was low compression.

 

[mcgann454]

No problem. The water heater only takes about an hour to heat up. Again, turning off one AC unit while cooking or other high load stuff and you can go much smaller.
Just curious, how did your 8BTD die? Mine was low compression.

Mine also. 90 lbs in cylinders 1 and 3.
Parts are crazy expensive. A friend is able to get a brand new 9KW unit with sound enclosure, remote panel and lift muffler for $9300 with 5 year warranty. Seems like a great deal.

 

[GGroves]

Did your old generator work fine with the stated loads? If so, that’s all you need. Of course if you get a good deal on the 9kw, go with that, but not larger.

 

[mcgann454]

Did your old generator work fine with the stated loads? If so, that’s all you need. Of course if you get a good deal on the 9kw, go with that, but not larger.

Got the boat with the old generator not working. I have since added the other air conditioner. It had two before, but the second was much smaller.
I think going from an 8KW to a 9KW should cover me.
The cost difference between a 7.5KW and 9KW is $1000.
My wife is used to all the comforts of home and a touch worried of spending two years on a boat, so I want to make it as easy as possible for her.
LOL

 

[Simi 60]

A slow spinning low maintenance generator would be my choice.
I have one and a woman to match.
No hairdryers, irons, hair straightener or air conditioner required.
Solar panels alone meet 90% of our needs but we do have a 7kva as backup.

 

[Ski in NC]

For your 9kW, get a 3cyl 1800rpm machine. Kubota, Shibaura, Isuzu and Mitsubishi are all good engines used by various gennie companies. Post brand and model you are looking at.

 

[mcgann454]

A slow spinning low maintenance generator would be my choice.
I have one and a woman to match.
No hairdryers, irons, hair straightener or air conditioner required.
Solar panels alone meet 90% of our needs but we do have a 7kva as backup.

Yes, I did the research and wanted the slow spinner for sure. I really like the Northern Lights.

As to the admiral, after 31 years it's cheaper to keeper. And if you tell her I said that, I will vehemently deny I wrote this.

 

[mcgann454]

For your 9kW, get a 3cyl 1800rpm machine. Kubota, Shibaura, Isuzu and Mitsubishi are all good engines used by various gennie companies. Post brand and model you are looking at.

The deal I got was for a new Cummins/Onan 9MDKDL.
I have not committed yet.
1800 RPM but it seems to have quite a bit of electronic monitoring.
I like the simplicity of the northern lights relays.
The price seems to be right, though.
I would love any feedback positive or negative.

 

[O C Diver]

I Looped last year with similar electrical needs, except 3 12K btu AC units. My 8KW Onan / Cummins with a 3 cylinder Kubota engine is a good size. Mine runs at 1,800 rpm, has a sound shield, lift and secondary muffler. Compared to a number of other Looper boats I was on, it is very quiet in the boat, and extremely quiet outside. Had a couple of canal side situations were shore power didn't work. Nice to be able to run the generator and nobody hears it to complain.

Ted

 

[O C Diver]

The deal I got was for a new Cummins/Onan 9MDKDL.
I have not committed yet.
1800 RPM but it seems to have quite a bit of electronic monitoring.
I like the simplicity of the northern lights relays.
The price seems to be right, though.
I would love any feedback positive or negative.

Mine is the MDKAL rated at 8KW, and vintage 2002. Other than normal maintenance, mine has been trouble free.

Ted

 

[Ski in NC]

Just checked Onan website. Looks like a good unit, 3cyl Kubota at 1800. Yes it has electronic controls and governor, but in my experience that particular Onan system has been quite reliable. And lots of them out there, that system has been in use for over ten years (?? pretty sure, maybe longer).

I have replaced a few controllers, but they were either in boats hit by lightning or where water dribbled on the gennie.

Keep it dry and it should be good.

These things have excellent voltage and frequency control. 120Vac and 60Hz at any load in the range.

 

[caltexflanc]

My wife is used to all the comforts of home and a touch worried of spending two years on a boat, so I want to make it as easy as possible for her.

This is great wisdom that served me well when we were cruising full time and spent most nights on the hook or a mooring. Everything I did in filling out the electrical system was designed to make it a no brainer as much as possible. Generator on: do whatever you want. Inverter (which i sized up to 4000w): this, this and this no, everything else yes... Even invested in an automatic generator start system .
Power management schmangement ... this is pleasure boating.. in that order!

We were in a mooring field once, and a neighboring woman left because she'd had it with her husband with this issue as the final tipping point.

 

[twistedtree]

Somebody alluded to it, but the key thing I see missing is your charger load, presumably from the inverter/charger?

Our heaviest gen load is after we have been at anchor and it's time to recharge the batteries, heat water, and maybe cook or do laundry. We hit 10kw no problem, probably closer to 12kw. But we have a lot of charger capacity (260A @ 24V), and a 3kw water heater. If at the same time we want to cool the boat down, then the HVAC will be on too and that will pretty much peg the 20kw generator. When doign an intial cool down, all zones want to run full tilt, so it's max load. If I'm on shore power (50A max), I typically will stage the zones to keep from tripping a breaker.

And don't worry too much about the generator load - within reason. As long as it gets a good exercise on a regular basis, some time at light loads will be just fine. Remember, it's there to serve you , not the other way around.

 

[Comodave]

We have a 9KW Onan in our 41’. Personally I would rather have a 7.5. I never come close to maxing out the 9KW. It is usually way underloaded unless we have both A/Cs running. But to charge batteries it is difficult to bring the load up to where I would like it.

 

[MYTraveler]

Since the marginal cost of additional capacity is relatively small (especially compared to the "cost" of not always having ample juice), in my opinion the limiting factor is your ability to keep the gen adequately loaded. If you need to run the genset 24x7, as I do, keeping it always adequately loaded is much more challenging than it would be if I ran it only when I need a bunch of electricity. Even so, I opted for 17kw units and have not regretted it.

 

[Gordon J]

My experience

I need to install a new generator.
The boat will be used for the loop.
The old generator was a Westerbeke 8KW 8BTD.
I have a 1984 Heritage East Nova Sundeck.
I have changed all of the lighting to LED and understand that does not have too much effect on he total needed.
I did add a second 18K btu air conditioner and have studied all of the threads on generators but would like a second opinion as I am unclear on what I should have so I have reserve wattage, but don’t under load the generator.
I also have a Victron multiplus with the spike protection that draws from the batteries for start up spikes if needed. I can’t find a start up amp spec for the air conditioners
Here is what I believe I would have on the hook cooking dinner in the Keys:
2) Dometic 18Kbtu air conditioners at 15.1 amps(15.1x120x2) 3624 Watts
Not sure of the draw for the two water pumps 370 Watts?
Norcold 6 cu/ft AC/DC FRIDGE/freezer .4 amps (.4x 120) 48 Watts
Two burner electric stove top 1200 Watts
Oven 1200 Watts
1200 watt microwave
20 Gal electric water heater 2000 watt
Tv and sound bar
Uline ice maker
If I add up all of the major appliances outside of the TV and Icemaker it totals to
9642 Watts.
Add the Charges/Inverter is another 15 watts?
I realize they might not all be on at the same time and I should turn some off if using others. I also read that a generator should be loaded between 30 and 70%.
I do have 6 100 watt solar panels I will be installing this year as well.
If I get a 9KW generator, I could potentially load it to 100%.
Does an 11 KW generator make sense?
Thanks in advance.

We have a 6 and 12 kw unit. We run the small one probably six to seven hours for each hour on the larger unit. 12 kw has about 1700 hours and was installed on the boat new in 2003. 6 kw was installed in 2010 and has nearly 2200 hours.

I seldom run all five air conditioners and equipment simultaneously.

 

[OldDan1943]

We have a 9KW Onan in our 41’. Personally I would rather have a 7.5. I never come close to maxing out the 9KW. It is usually way underloaded unless we have both A/Cs running. But to charge batteries it is difficult to bring the load up to where I would like it.

Remember, the new gen has to fit in the old spot too. have to have room for the new muffler too.

 

[mcgann454]

Since the marginal cost of additional capacity is relatively small (especially compared to the "cost" of not always having ample juice), in my opinion the limiting factor is your ability to keep the gen adequately loaded. If you need to run the genset 24x7, as I do, keeping it always adequately loaded is much more challenging than it would be if I ran it only when I need a bunch of electricity. Even so, I opted for 17kw units and have not regretted it.

Thanks everyone for the input.

I’m hoping I can exercise the house bank for most activity. I have 8 Trojan golf cart batteries for the house bank and the solar array to help with the load and then use the Genny when I need air and the kitchen.

If I run the two air conditioners and the charger as well as the water heater, I would be be looking at about 7200 watts or about 80% of a 9KW Genny.
Too much?
I would have to manage the energy use.

 

[OldDan1943]

Folks, it's all about load management. Sometime we have to be creative in our thinking, especially if we have a 30 amp boat.
Buy what you can afford and what fits in the available space comfortably.

Peak load, put some of it on the inverter.
My experience, 2 burners, coffee pot, 2 a/c, it fits.
Start adding in oven or even add in the mirowave, the boat trips off.
I move the microrwave to the inverter via switches, when necessary.
Sort of like what Dolly Parton said after a wardrobe failure, "Cant put 10 pounds of mud in a 5 pound sack."
Not only are we planning a meal but now timing the "which gets cooked first"
Just relax and plan.

 

[ranger58sb]

If I run the two air conditioners and the charger as well as the water heater, I would be be looking at about 7200 watts or about 80% of a 9KW Genny.
Too much?
I would have to manage the energy use.

I suspect most of that "management" would be about increasing load, not about shedding. Maybe some phase-in at the end of a day when you might need both ACs, hot water, battery charging, and want to cook at the same time... but even then, I wouldn't be surprised if you never max out 9 kW capacity. Especially with the solar augmentation...

We've never maxed out our 8 kW running everything... and we have no solar...

-Chris

 

[Aquabelle]

Your Victron MultiPlus with Battery Assist and a house bank of that size means little chance you will have to load shed. I have the same house bank, a Victron, x4 ac units, d/washer, m/wave, electric oven, a wife and teen daughter ......and my 10kW handles all. As an earlier post said, don't sweat underloading....maintain the gen properly and load it up when that makes sense and all will be well. Do you know why the old unit failed? Is there any installation or maintenance issue to learn from that?

 

[mcgann454]

Your Victron MultiPlus with Battery Assist and a house bank of that size means little chance you will have to load shed. I have the same house bank, a Victron, x4 ac units, d/washer, m/wave, electric oven, a wife and teen daughter ......and my 10kW handles all. As an earlier post said, don't sweat underloading....maintain the gen properly and load it up when that makes sense and all will be well. Do you know why the old unit failed? Is there any installation or maintenance issue to learn from that?

The generator got wet. That is one of the reasons I got the deal on the boat that I did.
So far it is still a deal I think.
LOL