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Old 05-06-2016, 01:07 PM   #21
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A few years ago I spent some time on a Northern Marine 57. It had 20 and 6 kw units as well as a decent inverter setup. The 6 kw unit did most of the work as far as keeping the house bank up even while at anchor. The 20s main hours were low in comparison to the 6, relegated to using AC, clothes washing and serving as a hydraulic pump source for the get home.

So many options I can't say one way for size decision is better, especially when taking into account not all of us base survival upon ACs up and running due to location.
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Old 05-06-2016, 01:22 PM   #22
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Certainly this would be a good argument for waiting on the second generator until after developing some solid numbers. Certainly pull wire and have all infrastructure in place for the second one. With solid use numbers, clearly 16 to 18 KW would have been a better all around fit for the boat.

Ted
17 was a consideration but then it wouldn't have been interchangeable and would have been overloaded with our maximum load, plus not completely interchangeable parts which we consider that a plus. There's no reason not to go with the 21.5 in our case. No load that is too little for it. Thinking logically, the boat normally only comes with the 21.5. That way too our max load to date of 14.3 would be 84% on the 17 and while that's our max load to date, I'm sure some day we'll top it. We did get all the numbers before deciding, so I certainly agree with you on that to get some real numbers, not just theory, before finalizing second generator.
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Old 05-06-2016, 01:22 PM   #23
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On a boat with 2 gen sets, when do you use each of these?

12 kw Northern Lights generator (2,672 hrs)
6 kw Northern Lights generator (1,163 hrs)
12kw - durning the day for hotel service

6kw - at night after dinner when the load is light
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Old 05-06-2016, 01:25 PM   #24
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A few years ago I spent some time on a Northern Marine 57. It had 20 and 6 kw units as well as a decent inverter setup. The 6 kw unit did most of the work as far as keeping the house bank up even while at anchor. The 20s main hours were low in comparison to the 6, relegated to using AC, clothes washing and serving as a hydraulic pump source for the get home.

So many options I can't say one way for size decision is better, especially when taking into account not all of us base survival upon ACs up and running due to location.
Location means a lot. We almost always have A/C on, except the last few days in NY, running heat, but same issue. We do a lot of laundry and cook a lot. Seems most of the females have long hair so lots of shower time and hot water.

If we hadn't added additional freezers then we would have had a different picture. We have switchable units but normally running 3 freezers and one refrigerator.
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Old 05-06-2016, 01:27 PM   #25
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12kw - durning the day for hotel service

6kw - at night after dinner when the load is light
Our load doesn't lighten as much as others seem to.

In fact with 43-46 degree nighttime temperatures right now, ours would be heavier at night if we were anchoring.
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Old 05-06-2016, 01:30 PM   #26
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I have the exact same generators on my 2003, Ocean Alexander 456. I have owned the boat only for about a month. Typically if I am only charging the batteries and using one air-conditioner, or the stovetop , I will use the 6KW period. All five air-conditioners are 220 V. The 6KW will run the 220 V air conditioner water pump and two of the smaller air-conditioners. All else requires The 12 KW.

For what it's worth, the previous owners ran the 6KW much more than the 12 KW.
The 12 KW has about 1800 hours but was original to the boat. The 6KW was installed in 2010 and it has about 1500 hrs.

Obviously, if I were to run both the flybridge air-conditioners as well as the three below decks, I would need to run the 12 KW.

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Old 05-06-2016, 02:23 PM   #27
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17 was a consideration but then it wouldn't have been interchangeable and would have been overloaded with our maximum load, plus not completely interchangeable parts which we consider that a plus. There's no reason not to go with the 21.5 in our case. No load that is too little for it. Thinking logically, the boat normally only comes with the 21.5. That way too our max load to date of 14.3 would be 84% on the 17 and while that's our max load to date, I'm sure some day we'll top it. We did get all the numbers before deciding, so I certainly agree with you on that to get some real numbers, not just theory, before finalizing second generator.
Guess I misunderstand what you wrote. When you said 14 KW was your maximum, I assumed it was everything turned on at full load .

BTW, it looks like Cummins / Onan offers two 17.5 KW units. One identical to your 21.5KW but turning 1500 instead of 1800 RPM.

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Old 05-06-2016, 02:59 PM   #28
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Guess I misunderstand what you wrote. When you said 14 KW was your maximum, I assumed it was everything turned on at full load .

BTW, it looks like Cummins / Onan offers two 17.5 KW units. One identical to your 21.5KW but turning 1500 instead of 1800 RPM.

Ted
I was comparing to their regular 17 kw unit. The other 17.5 you mention is 50 Hz. I was saying just over 14 kw was our maximum to date. It's not our theoretical maximum and I do anticipate more sometime. But even with say 14.3 kw usage I wouldn't use a 17 kw generator as that would put it at over 84% load.

Sorry I was a little unclear. The real issue is that the 21.5kw generator was the sizing the builder felt appropriate for that boat and I don't see us ever loading it less than 6 kw which is 28% and generally not under 9 kw which is 42%. So, I'm very comfortable with the 21.5 kw for both the primary and second generator.

Now I see someone else posting that they've almost exclusively used their 6 kw instead of 12 kw. Everyone's usage is different. That's running 2 of the smallest A/C's out of his 5 units. That's not a pattern we would ever fit in. The only A/C we sometimes would not be running is the flybridge.

We could easily get by with just one 21.5 kw gen. The worry of it being down for a while is my main reason for having two and in our case since the second is for backup purposes then makes sense to be the same.

Obviously if you can operate on a smaller unit, that's fine. However, the argument that it was more economical to operate and the argument over load are both weak. At 1/4 load a 21.5 uses 0.8 gph. At 1/2 load an 11.5 uses 0.7 gph. So with the same load, minimal difference in fuel usage.
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Old 05-06-2016, 05:22 PM   #29
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and when on ship you have 2 generators same size don't try to equalize hours, give 1000 hours difference because if you give same hours when problem happen on one you get same problem on other one and you can you in trouble...
so that better to give big difference

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Old 05-06-2016, 05:40 PM   #30
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and when on ship you have 2 generators same size don't try to equalize hours, give 1000 hours difference because if you give same hours when problem happen on one you get same problem on other one and you can you in trouble...
so that better to give big difference

Hugues
No two generators are going to give trouble at exactly the same hours. Just not going to happen. You might be years apart.
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Old 05-07-2016, 06:50 AM   #31
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"What are people's thoughts? Any reason not to go electric for the get home?"

It would really depend on the boe thruster setup, as it will be used hundreds of times more than emergency propulsion.

Only a Hyd bow thruster can be used for long periods of time, so a noisemaker that can feed the thruster with the main engine at idle is really nice.
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Old 05-07-2016, 09:06 AM   #32
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Only a Hyd bow thruster can be used for long periods of time, so a noisemaker that can feed the thruster with the main engine at idle is really nice.
That leads me to another question.
I thought most thrusters shut down from over heat so what would the advantage of a generator feed other than doing away with batteries?
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Old 05-07-2016, 09:22 AM   #33
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That leads me to another question.
I thought most thrusters shut down from over heat so what would the advantage of a generator feed other than doing away with batteries?
The generator has a hydraulic pump on it for the bow thruster. Since the generator is at a constant rpm, the performance remains the same with a 100% duty cycle.

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Old 05-07-2016, 09:53 AM   #34
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The generator has a hydraulic pump on it for the bow thruster. Since the generator is at a constant rpm, the performance remains the same with a 100% duty cycle.
Thanks again, Ted. I was stuck on electric and didn't connect the hydraulic dots.



Too early in the morning on the west coast for me to try thinking.
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Old 05-07-2016, 10:18 AM   #35
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That leads me to another question.
I thought most thrusters shut down from over heat so what would the advantage of a generator feed other than doing away with batteries?
There is a bit of urban myth regarding electric thrusters kicking out due to overheat. Often the kick out is due to wiring, batteries or switchgear being the issue. My bow thruster will stay engaged for over 30 seconds without a kick out, the longest I have ever needed it. The better electric thrusters made today will run for a very long time, purportedly they are designed to do this.

Hydraulic systems have a shelf life as hoses, O rings and fittings age. Not trouble free at all. Some builders hide this plumbing in the darnedest of places
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Old 05-07-2016, 10:32 AM   #36
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There is a bit of urban myth regarding electric thrusters kicking out due to overheat...Hydraulic systems have a shelf life as hoses, O rings and fittings age. Not trouble free at all. Some builders hide this plumbing in the darnedest of places.
Having spent some time around heavy equipment and seeing the frequency of hydraulic line failure, I have looked at hydraulic thrusters a bit askance. It's a lot easier to deal with oil on a dozer than a DeFever.
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Old 05-07-2016, 08:24 PM   #37
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Hawg-we have a 20KW and a 12KW. We normally use the 12KW almost exclusively. We only have to use the 20KW if we use the AC


seriously? You are burning upto 12KW without ac? wow.
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Old 05-07-2016, 08:53 PM   #38
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Having spent some time around heavy equipment and seeing the frequency of hydraulic line failure, I have looked at hydraulic thrusters a bit askance. It's a lot easier to deal with oil on a dozer than a DeFever.

Yeah and no. Lines on a dozer take FAR more abuse then some lines clamped to a bulkhead or in a PVC chase. Most of what I've heard and seen hydraulically failing on boats are seals.
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Old 05-07-2016, 10:00 PM   #39
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3 Blue Sea MEGA fuses, 2 Blue Sea 6 fuse blocks and 2 circuit breakers.
Thanks Archie. Gave me something to look up and now I know.
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Old 05-07-2016, 10:04 PM   #40
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Yeah and no. Lines on a dozer take FAR more abuse then some lines clamped to a bulkhead or in a PVC chase. Most of what I've heard and seen hydraulically failing on boats are seals.
Still messy though huh?
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