Two Generators

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catalinajack

catalinajack

Guru
Joined
Nov 16, 2011
Messages
3,585
Location
USA
Vessel Name
Catalina Jack
Vessel Make
Defever 44
Our Defever44 came with two generators which, I believe, were original to the boat. One is a Perkins-powered 12.5Kw Kohler. The other is a 7.7Kw Westerbeke. Both have about about 2,400 hours usage. Having two generators is nice for redundancy and using the smaller one is more efficient for lower power demands. However, that second generator takes up a lot of space. I am seeking opinions. Should I have the Westerbeke removed or should I keep it? Th Westerbeke is extremely difficult to service. To replace the raw water pump impeller, the alternator must be removed to get at the pump which also must be removed. Wrenching all of it out of there is a bear so I am much inclined to just get rid of it.
 
My first impression is that I am not inclined to remove things from the boat.

That said, I think the two generator concept is a bit more applicable to boats larger than your 44' aft cabin. With careful load managment I do not see where your 12 KW could not handle the loads without being underloaded.
 
Do you already have a large house battery bank and inverter/charger?
 
I have 2 14kw generators, it's nice to have a spare. But as High Wire alluded, an inverter with a good battery bank is also a backup.
Since I ditched the electric stove, added a better inverter, my power needs dropped considerably. Should I choose, I can charge the house banks with the mains. I only need the high output if rafting and supplying power to others.
Another method for servicing your generator, mount it on sliding rails if there is space to slide out. In service, bolts secure the rails but are removed to slide. It requires slack electric, fuel and water lines, and easy disconnects on the exhaust, etc.
 
I have long thought about a similar setup. Rather than a larger 7.5-10K, it would be nice to have a 3K and a 5K, for example. (Obviously sized will vary based on the overall size of the vessel and power demands).

It is my understanding they size the generator for a 'worst case scenario' where a Heat/AC, stove/oven, water heater, battery charger are all running at the same time. However this is rarely the case. In most cases, I'm just recharging the batteries. In this case, the load on the generator is low (to low??).

It would be nice to be able to fire up a 3K for light loads. A 5K for medium loads, and both for heavier demands.

This leads to a question.....

Can you have two generators running together? If so, do you need to split the circuits those generators are feeding?
 
I believe in simplification, but removing it won't be an easy task either, including all the wiring/switches etc....

Good question though, no easy answer...
 
Shrew said:
This leads to a question.....

Can you have two generators running together? If so, do you need to split the circuits those generators are feeding?
Click to expand...

You can run both generators at the same time IF there is ABSOLUTELY NO WAY to connect the outputs together. The AC waveforms of the outputs must be exactly matched before tying them together or else one or both generators will be catastrophically destroyed.
Its called "paralleling" the generators. Larger machines can be paralleled with a Synchroscope and remotely controlled output breakers. High dollar megayacht stuff.

In todays marine generator market for smaller powerboats it is not available. Honda Inverter series portables can. Maybe someday their inverter technology will spread to installed marine gen sets for yachts.
 
Mr Murphy will frown on you if you take out your backup gennie. Next cruise afterward, the Kohler will poop. Just the way things seem to work. Highly technical, I know.

On a serious note, I would rather have one brand new gennie than two old ones. For numerous reasons, gennies can be way more of a PITA than main engines. Perhaps you could sell both as running proven takeouts, and offset the cost of a new one.

If you want to keep the old Kohler, keep the Westy too.
 
If you have the room keep both. I would love to have a backup to my Westerbeke 8kw. If I were starting from scratch I would have two smaller generators.

Having almost faced the necessity of replacing my generator (ouch!) to have two on board so that if one fails I didn't have to buy another one would be wonderful.
 
Last edited:
Larry M said:
If you're happy with the Kohler, I'd remove the Westerbeke.
Click to expand...

Or the other way around. Do you REALLY find many chances to load up a 12.5KW genset? I struggle to put a decent load on my 7.5KW.
 
CaptTom said:
Or the other way around. Do you REALLY find many chances to load up a 12.5KW genset? I struggle to put a decent load on my 7.5KW.
Click to expand...

I agree but I'll leave the loading question to the OP, Catalinajack. I believed he's owned the boat for awhile.

We have an 8kw Northern Lights on Hobo. If it were to die, I'd put their 6Kw in as the replacement. I would like to load the 8kw more than I do.
 
I would be happy with a 6KW instead of an 8KW, but my 8KW is a slow speed (1,800 RPM) and most of the smaller units are high RPM (noisier ).

Ted
 
Plenty of 1800rpm 3cyl 5-6kW machines available. NL, Westerbeke, other brands.
 
CaptTom said:
Or the other way around. Do you REALLY find many chances to load up a 12.5KW genset? I struggle to put a decent load on my 7.5KW.
Click to expand...

On our DF loading up the 12.5 is not a problem. Reverse cycle air, washer, dryer, battery charging, all electric galley and water heater will max it out.
 
I removed two generators, a 7.5 Onan and a 2.5 Mase. Both were running, sold as running take outs. Both were an unpredictable expense waiting to bite me at an inconvenient time IMO. I do have a Honda 2000 that I sometimes use, I run it every 3 months whether I need to or not.

Should the OP remove one or both his? All depends. Start out with a blank spreadsheet (or sheet of paper if you enjoy math) and list your loads to determine average and peak loads, and Ah consumed per day. After that it is easy: right sized alternators, house bank and inverter, solar panels will do it if you don't want/need aircon.

In my case: 2 x 200A Leece Neville alt, 1284 Ah AGM house bank, 3000 VA inverter/charger (prob should have been 5000) and 2070 W solar. I occasionally use the washer at anchor (sunny days), but only run the dryer when on the move. Propane cooktop. Webasto hydronic heating, loops for hot water via Webasto and engine.

Whether 2,1 or 0 gennies work for you will depend on a full systems review.
 
You could always run the proper engine pickeling procedure and just forgetaboutit.
 
We have a 5.5kw Northern Lights and that runs at 1800, they now call it 6.0kw. Been very happy with it, handles everything we need.
 
I have known a couple of boats where the captain felt he had a hard time loading his 12kw generator. Thus when he wanted to use the washing machine he also turned on one of the AC units to cool an empty section of the boat.

Our 8kw runs everything. We do exercise power management. Chiefly in the first ten minutes of generator run when both chargers and the water heater are running at max. We do not then also turn on a hair dryer and/or the microwave. If necessary I have turned off one charger or the water heater for 10 minutes.

I can tell when the load is affecting the generator. I have a frequency meter which reads the output. A drop from 60.5 hertz to 57 hertz is enough of a load for me. i will not then add more load.
 
sunchaser said:
On our DF loading up the 12.5 is not a problem. Reverse cycle air, washer, dryer, battery charging, all electric galley and water heater will max it out.
Click to expand...

Same on board our Defever. The smaller 7.7 Westerbeke will not run all three Cruisairs simultaneously. And thanks to all who responded and offered their thoughts. At least for the time being I have decided to keep both generators. I will tackle changing the impeller on the Westerbeke later this year. Right now I have too many projects lined up ahead of this task. As some have suggested the 7.7 can be used with wise load management. Running all three A/C's at the same time will rarely be necessary.
 
Last edited:
catalinajack said:
Our Defever44 came with two generators which, I believe, were original to the boat. One is a Perkins-powered 12.5Kw Kohler. The other is a 7.7Kw Westerbeke. Both have about about 2,400 hours usage. Having two generators is nice for redundancy and using the smaller one is more efficient for lower power demands. However, that second generator takes up a lot of space. I am seeking opinions. Should I have the Westerbeke removed or should I keep it? Th Westerbeke is extremely difficult to service. To replace the raw water pump impeller, the alternator must be removed to get at the pump which also must be removed. Wrenching all of it out of there is a bear so I am much inclined to just get rid of it.
Click to expand...

I would ask three questions. First, do you ever have to run both of them together? The fact they have the same hours makes me curious about that. Second, do you ever require them 24 hours a day, more during day and less at night? If so, I think there's value to the larger for day and smaller for night. Third, where and what type cruising do you intend? If my plans were to go cruise the Caribbean, then I'd absolutely want two generators. If my plans were the Chesapeake Bay then I probably wouldn't.
 
The PO of our boat installed a 6kw NL eventhough it already had a NL 12KW. The smaller one was ibstalled when the now 14-year-old boat was only 7 yrs old. Now the smller one has 500 more hours than the big one.

I too wish I had the space, but once had a 6kw go bad in Grenada. Took a while to repair and Grenada was Hotter than Hades in October. I like the idea of having back-up and hate the thought of uninstalling a working system. I also think I must be saving quite a bit of fuel using the smaller one when nor running now than three ACs.

Gordon
 
14.9 KW per hour equals 20 HP which is about how much a diesel can produce for an hour using gallon of fuel

SO you can estimate how much fuel you are using fairly simply
 
Our boat is much smaller so we would never have large demands for AC power. Rarely need air conditioning in our waters so our 7.5KW generator's usage is limited. And today with solar and inverters it is used even less. My preference is to add additional solar to our existing 600 watts and maximize silence's tranquility.
 
bayview said:
14.9 KW per hour equals 20 HP which is about how much a diesel can produce for an hour using gallon of fuel

SO you can estimate how much fuel you are using fairly simply
Click to expand...

For clarity I should have added it is the KW consumed not the KW possible.

So a 7KW consumption, half load, would use 0.5 Gph
 
bashu said:
Does this inverter have a 3 stage charger, is there a recommended monitoring system, does it have an equalization mode?
Click to expand...

Also have the 2812. It is three stage, Magnum sells a monitor, requires you buy the remote panel. I use the Link series as well. The 2812 has an equalization stage which is good for three hours.
 
"I will tackle changing the impeller on the Westerbeke later this year."

Frequently removing the slotted head screws holding on the cover plate is a PIA.

SS Hex head screws are easier to remove or install as seeing the head is not required.

"As some have suggested the 7.7 can be used with wise load management. "

Starting the 3rd unit is usually the hassle , a pass thru inverter canboost the extra load for a second and all 3 will run. Seamless.
 
Consider the trim of the boat if you remove heavy items - especially if you delete a lot of weight low in the boat.
 
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