Two Generators

Why do some boats in the 40' to 60' range have two gensets? Just redundancy?
Example-One 48' Hatteras I've seen on line has a 15kw and a 9kw and others are similarly equipped.

That seems like a lot for a boat that size. You could remove one and free up a lot of engine room space.

Ken

ktdtx said:

Why do some boats in the 40' to 60' range have two gensets? Just redundancy?
Example-One 48' Hatteras I've seen on line has a 15kw and a 9kw and others are similarly equipped.

That seems like a lot for a boat that size. You could remove one and free up a lot of engine room space.

Ken

Click to expand...

Yes. I wouldn't remove them. Also might be a "night" or "cruise" genny to run a couple Ac's at night.

ktdtx said:

Why do some boats in the 40' to 60' range have two gensets? Just redundancy?
Example-One 48' Hatteras I've seen on line has a 15kw and a 9kw and others are similarly equipped.

That seems like a lot for a boat that size. You could remove one and free up a lot of engine room space.

Ken

Click to expand...

Not necessarily just redundancy....depending...some have drastically different load needs.

Some travel from cold to hot with temperate inbetween...so full loading where big AC and Heat systems may require the 15kW and other times the 9Kw is better loaded.

My friend had a 55 Viking that had 2 -20kWs...way overkill but the PO wanted FULL redundancy.

My redundancy on my 40 footer is a 1kW Honda for my 8kW Westerbeke.

That is too small now that I upgraded my battery charger but I can still rig my 25 amp charger and charge batteries and run DC equipment for 8 hours on less than a gallon of gas.

I doubt to many 40 footers have 2 big diesel gensets in them...not till you get tup o 50 foot or more flushdecks with walk in engine rooms.

We have an 8kw and a 20kw on a 58' boat. While on the move, or anchored, the 8kw handles the loads for all 120VAC items. Our AC, W/D and water heater are 240 VAC and if the AC and or W/D is in use, we need to use the 20kw. Our 20kw has about 35% of the hours that the 8kw does. The 8kw burns less than half the fuel of the 20kw.

You gotta remember allot of these boats were built "back in the day"

Back in the day we did not have inverter technology like we have today.

That is one of the reasons many boats in that size range had smaller cruise generators.

Today much of that need has gone away. We have inverters up to several kilowatts that will run the smaller AC loads, making the generators job recharging the batteries and taking care of larger loads like Air Conditioning.

Thats not to say that two generators is not a good thing. Redundancy is great. Its saying that the need for two generators on boats in the 50' range has diminished with inverter technology.

Gonna say...this coming from a generator guy?

On the 58' Kady Krogen, they have a 12 KW and a 20KW genny. The 12 is for when you are only running to charge the batteries, maybe the A/C and the lights. If you want to run everything, dishwasher, trash compactor, micro wave, washer/dryer and all the other stuff, you use the 20 KW. You shouldn't run the genny under a small load. So, you have a "small load" 12KW and a "big load" 20 KW. I know, it sounds crazy. Doesn't it? I have a 2.7 KW on my 27 foot tug. That Kady Krogen was 2.9 mill!

chester613 said:

On the 58' Kady Krogen, they have a 12 KW and a 20KW genny. The 12 is for when you are only running to charge the batteries, maybe the A/C and the lights. If you want to run everything, dishwasher, trash compactor, micro wave, washer/dryer and all the other stuff, you use the 20 KW. You shouldn't run the genny under a small load. So, you have a "small load" 12KW and a "big load" 20 KW. I know, it sounds crazy. Doesn't it? I have a 2.7 KW on my 27 foot tug. That Kady Krogen was 2.9 mill!

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That's about right for the boat. We have a 12kw but really need a 16kw to suffice our needs. I know some people with a N60 they have a 9kw in the lazz and a 20kw main genny in the ER. Nothing crazy.

psneeld said:

Gonna say...this coming from a generator guy?

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Oh, no. This a single vs twins debate. And to the OP, you could remove one and free up a lot of engine room space.

Larry M said:

Oh, no. This a single vs twins debate. And to the OP, you could remove one and free up a lot of engine room space.

Click to expand...

Or leave it and get rid of the engine for an electric main propulsion conversion.....new thread

Greetings,
"...and free up a lot of engine room space." So you can stow all your anchors in there. BONUS!

There is also another thing to consider...

If you have say 1500 watts of Air Conditioning that runs at for discussion sake a 33% duty cycle on a typical evening you might be actually better off running that on an inverter.

Lets do some math regarding that. 1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

With no other loads applied you could run all night long and not have to run your generator if you had around 800 amp hours of battery.

If you had a higher load or higher duty cycle you could use a State Of Charge meter and tie that to an auto start on your generator. Then when the batteries got low the generator would automatically start up, charge your batteries, then turn itself off.

You could even use a system like that to keep your batteries charged while you were anchor'd off and playing on shore all day, or stuck on a mooring bouy and off the boat for a few days exploring.

Defever 44 owner here. Boat came with a 12.5 kw Kohler and a 7.7 kw Westerbeke.

I thought if I freed up that space I could store a lot more anchor chain

As others have said, two reasons. Backup and to balance to load.

Single main but two gensets on my KK54 - go figure!

I have an 8kW and a 20kW NL. The 8 is in the lazarette and the 20 in the ER. With 4 cruisairs, WD, etc it's possible to load up the 20kW. Most of the time the 8kW has enough to satisfy my needs.

I may add a hydraulic get home motor to the 20kW. Others have done the same and it seems like good use of all that extra power.

Richard
Stillwater
KK54 #5

Two 17 kw's. Only for redundancy.

"1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery

125Amps for 8 hours is 1000AH which would require about 2200AH from the batt set as this discharge would be at an 8 hour rate , not the std 20 hour rate.

A guess would be a ton (2000lbs+) of LA batteries that would require 10-12 hours of a 125A charge to be refilled.

Double the battery price and they might be refilled faster , with a hefty 200A+ charge source.
********
Two sized noisemakers are to assure the minimum load will be enough not to underload the diesel, and shorten its service life.

ksanders said:

There is also another thing to consider...

If you have say 1500 watts of Air Conditioning that runs at for discussion sake a 33% duty cycle on a typical evening you might be actually better off running that on an inverter.

Lets do some math regarding that. 1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

With no other loads applied you could run all night long and not have to run your generator if you had around 800 amp hours of battery.

If you had a higher load or higher duty cycle you could use a State Of Charge meter and tie that to an auto start on your generator. Then when the batteries got low the generator would automatically start up, charge your batteries, then turn itself off.

You could even use a system like that to keep your batteries charged while you were anchor'd off and playing on shore all day, or stuck on a mooring bouy and off the boat for a few days exploring.

Click to expand...

FF said:

"1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery

125Amps for 8 hours is 1000AH which would require about 2200AH from the batt set as this discharge would be at an 8 hour rate , not the std 20 hour rate.

A guess would be a ton (2000lbs+) of LA batteries that would require 10-12 hours of a 125A charge to be refilled.

Double the battery price and they might be refilled faster , with a hefty 200A+ charge source.
********
Two sized noisemakers are to assure the minimum load will be enough not to underload the diesel, and shorten its service life.

Click to expand...

Now Now FF, I for discussion sake indicated a 1/3 duty cycle... See it in red in my original post above... Read carefully and I think you'll find my math is probably correct.

ksanders said:

Now Now FF, I for discussion sake indicated a 1/3 duty cycle... See it in red in my original post above... Read carefully and I think you'll find my math is probably correct.

Click to expand...

Perhaps FF was including the water pump,

Lets see...

That adds at least another 20 Ah to the draw (100 watts/12 volts =8.3a X 8 hours X .33 duty cycle =21.91Ah

Nope still works, but you would be giving the bank a good workout everyday charging and discharging. Like a U-boat.

A few weeks ago I was anchored out and left my water heater (1200W) turned on while I was on my inverter. I had used up about 300Ah of battery by the next morning!

Richard

My ACs don't pump when the compressor cycles off...but the fan still runs.

psneeld said:

My ACs don't pump when the compressor cycles off...but the fan still runs.

Click to expand...

None should,

That's why I used the same 33% duty cycle in my formula.

SCOTTEDAVIS said:

None should,

That's why I used the same 33% duty cycle in my formula.

Click to expand...

why?

""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


Bob

BobH said:

""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


Bob

Click to expand...

You're not missing anything. The problem was with both terminology and math. What you wrote is correct

Richard

SCOTTEDAVIS said:

None should

Click to expand...

Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.

Capt.Bill11 said:

Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.

Click to expand...

We I'm glad they don't any longer as it is they suck enough crap into the strainer when they need to be sucking, I don't need them sucking in stuff when they don't need to be.

psneeld said:

why?

Click to expand...

Why? What?