OK, thanks, Ted.Well I would use the 6 KW unless loads exceeded 75% of capacity and then switch to the 12 KW.
Now that challenges my logic. How would you determine a common size that is not constantly over or under loaded? Unless, maybe in cases like yours in FL, your loads seldom vary day to day, day to night. Is that it?BandB; said:Now, if I was designing a boat, I'd just go with two equal generators 95% of the time. That way you can rotate them and prolong lives.
OK, thanks, Ted.
So using simple math when the 6KW hits 75% and you switch to the 12 KW would it's load then be around 25% and would that be too light for it?
There is reverse air and a water maker. Can the water maker be run under way?
OK, thanks, Ted.
So using simple math when the 6KW hits 75% and you switch to the 12 KW would it's load then be around 25% and would that be too light for it?
There is reverse air and a water maker. Can the water maker be run under way?
Yeah, I was using a Taiwanese calculator and it leaks.FWIW, 75% of 6 Kw is 4.5 Kw. 4.5/12 = 37.5%.
My boat didn't come with a get home motor. I've been eyeing up my 20K generator as a power source. I started thinking in terms of hydraulics, but now I'm considering an electric motor.A larger genset combined with a smaller one allows for the installation of a hydraulic get home system driven off the lesser used larger unit...
Besides what appears to be a belly up cock a roach over there in the corner, what am I looking at here?FF; said:Have you thought about a few load shedding relays?
Now that challenges my logic. How would you determine a common size that is not constantly over or under loaded? Unless, maybe in cases like yours in FL, your loads seldom vary day to day, day to night. Is that it?
What are people's thoughts? Any reason not to go electric for the get home?
Richard
Those who argue for the smaller unit quote a rule of not running under 50% load. That is not the rule applicable on current generators. The boat we're on at the moment came with one 21.5 kw generator. We added a second identical as a back up and to reduce wear. Our minimum requirement has been around 6 kw, our average has been around 11 kw and our maximum just over 14 kw.
We did extensive calculations and testing on this boat and the factory installed 21.5 unit before concluding what to do with the second generator. The answer was either skip it, or get a duplicate.
Besides what appears to be a belly up cock a roach over there in the corner, what am I looking at here?
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
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)
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.
12kw - durning the day for hotel service
6kw - at night after dinner when the load is light
Guess I misunderstand what you wrote. When you said 14 KW was your maximum, I assumed it was everything turned on at full load .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.
Ted
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