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Old 04-08-2016, 21:12   #1
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How do you choose a GENSET?

I have been doing a lot of research on generators since I am about to purchase my first Catamaran. I've looked across the board and would like some advice on which one is the most reliable as well as easier to service/find spares. I've been looking specifically at the Onan 11KW 60Hz versus the Northern Lights 9KW 60Hz.

Any thoughts would be greatly appreciated.
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Old 04-08-2016, 21:50   #2
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Re: How do you choose a GENSET?

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Originally Posted by Divedoug68 View Post
I have been doing a lot of research on generators since I am about to purchase my first Catamaran. I've looked across the board and would like some advice on which one is the most reliable as well as easier to service/find spares. I've been looking specifically at the Onan 11KW 60Hz versus the Northern Lights 9KW 60Hz.

Any thoughts would be greatly appreciated.
Where do you plan to cruise? Parts and support can be critical if your depending on your generator to be the mainstay of your power source needs. Look up the support network of the particular supplier. How quickly can they get a needed part to you in a less than popular part of the world.
Is this your only source of dependable energy?
I have a Norhtern Lights generator, it's rugged as can be, it's been stone dependable, runs my refrigeration, battery charging, RO systwem, water heating and device charging simultaneously but I'm still adding solar and wind generated power alternatives to my arsenal.
World wide support? Im sure you can find their parts/support network on their websites. Or, carry critical spares onboard, it's cheap insurance.
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Old 04-08-2016, 22:27   #3
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Re: How do you choose a GENSET?

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Originally Posted by Divedoug68 View Post
I have been doing a lot of research on generators since I am about to purchase my first Catamaran. I've looked across the board and would like some advice on which one is the most reliable as well as easier to service/find spares. I've been looking specifically at the Onan 11KW 60Hz versus the Northern Lights 9KW 60Hz.

Any thoughts would be greatly appreciated.
What size of a catamaran? Those are very heavy gensets -- can you afford the weight? Cats are very sensitive to loading.

You can probably do without a generator altogether if you are not using air conditioning heavily -- you can use one of the main engines as a generator by adding a heavy duty alternator. Also most cats have decent options for mounting solar panels.

If you need the genset for air conditioning, then you should size the generator carefully in order not to be dragging around more weight than you need. You don't have to consider the startup loads for the AC if you include, as you should, power boosting inverters in your electrical system. These allow you to size the generator closer to average rather than peak load.


As to makes of generators -- Northern Lights is considered the "gold standard", but all of the heavy duty, low speed, continuous duty rated generators are good: Onan, Kohler, etc. Northern Lights makes the smallest true heavy duty generator I know. I have a Kohler on my monohull, which has been superbly reliable and is very quiet, and produces clean power.


On a cat, however, where excess weight quickly destroys sailing performance, I might consider something lighter, even at the expense of the durability and quiet of a heavy duty generator, if I thought I really had to have a generator at all.
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Old 04-08-2016, 22:50   #4
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Re: How do you choose a GENSET?

I am going to make a radical assumption... Given that the OP has called himself Divedoug68, I'm assuming that he wants the generator to run a dive compressor
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Old 04-08-2016, 23:09   #5
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Re: How do you choose a GENSET?

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I am going to make a radical assumption... Given that the OP has called himself Divedoug68, I'm assuming that he wants the generator to run a dive compressor
Well, you don't need an 11kW generator to run a dive compressor (!).

If I were setting up a nice long range cruising catamaran from scratch, I would manage electricity this way:

1. Very large heavy duty alternators on both main engines, driven by serpentine belts, at least 3kW each, with Balmar regulation (the kind that lets you derate them).

2. Large solar installation.

3. A decent sized LiFePo battery bank.


The huge acceptance rate of LiFePo batteries allows you to charge efficiently with short generator runs, making it practical to use main engines for this (which don't like long runs with light loads).

In my opinion, two diesel engines on a catamaran is quite enough.

This kind of system wouldn't be too good for running air conditioning continuously at anchor. But query whether it's worth dragging around all that weight, just to have that capability. Most cruisers in the tropics are pretty happy using wind scoops at anchor, and A/C at the dock.
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Old 04-08-2016, 23:44   #6
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Re: How do you choose a GENSET?

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Well, you don't need an 11kW generator to run a dive compressor (!).

If I were setting up a nice long range cruising catamaran from scratch, I would manage electricity this way:

1. Very large heavy duty alternators on both main engines, driven by serpentine belts, at least 3kW each, with Balmar regulation (the kind that lets you derate them).

2. Large solar installation.

3. A decent sized LiFePo battery bank.


The huge acceptance rate of LiFePo batteries allows you to charge efficiently with short generator runs, making it practical to use main engines for this (which don't like long runs with light loads).

In my opinion, two diesel engines on a catamaran is quite enough.

This kind of system wouldn't be too good for running air conditioning continuously at anchor. But query whether it's worth dragging around all that weight, just to have that capability. Most cruisers in the tropics are pretty happy using wind scoops at anchor, and A/C at the dock.
My understanding is that you need at least 6kw to run the smallest Coltri dive compressor. The OP did also mention a 9kw as well as the 11kw.
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Old 05-08-2016, 00:38   #7
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Re: How do you choose a GENSET?

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My understanding is that you need at least 6kw to run the smallest Coltri dive compressor. The OP did also mention a 9kw as well as the 11kw.
Dozens of models with much smaller power requirements. Bauer Junior II starting from 1.5kw..

BR Teddy
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Old 05-08-2016, 00:58   #8
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Re: How do you choose a GENSET?

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Dozens of models with much smaller power requirements. Bauer Junior II starting from 1.5kw..

BR Teddy
I've been told that you need 6 to 7 time the nominal current to start the compressor
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Old 05-08-2016, 02:19   #9
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Re: How do you choose a GENSET?

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Well, you don't need an 11kW generator to run a dive compressor (!).

If I were setting up a nice long range cruising catamaran from scratch, I would manage electricity this way:

1. Very large heavy duty alternators on both main engines, driven by serpentine belts, at least 3kW each, with Balmar regulation (the kind that lets you derate them).

2. Large solar installation.

3. A decent sized LiFePo battery bank.


The huge acceptance rate of LiFePo batteries allows you to charge efficiently with short generator runs, making it practical to use main engines for this (which don't like long runs with light loads).

In my opinion, two diesel engines on a catamaran is quite enough.

This kind of system wouldn't be too good for running air conditioning continuously at anchor. But query whether it's worth dragging around all that weight, just to have that capability. Most cruisers in the tropics are pretty happy using wind scoops at anchor, and A/C at the dock.
Good advice.

Power to start a compressor is an issue. The solution is to fit the compressor with a three phase motor and drive it with an inverter. A 2kw motor will need barely more than a 2kw inverter to start it.

I don't know why cats don't have really big alternators with maybe an auto throttle control to control output or fit a speed controller and an ac head to turn it into a real be set.It would cut weight, reduce maintenance and cost a lot less.
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Old 05-08-2016, 02:47   #10
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Re: How do you choose a GENSET?

Greetings and welcome aboard the CF, Divedoug.
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Old 05-08-2016, 03:02   #11
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Re: How do you choose a GENSET?

First step: Define what you want to power and for how long.

Most of the rest, you've seen in this thread is speculation guessing at what you want to power.
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Old 05-08-2016, 05:37   #12
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How do you choose a GENSET?

I would highly recommend the Northern Lights. I have 3085 hours on my 5kw unit and have had no problems. We run 1 16000 BTUH water to air heat pump, Hot water, Microwave, TV w tracking antenna, Inverter/charger, multiple laptops, IPads, IPhones and I am rarely loaded up. You will definitely want a sound enclosure as the lower sound level is worth it. We run HVAC continuously while underway, most cruisers probably don't but that was a condition my wife and I wanted to maintain and I am glad I did. I burn about 6 gallons of fuel in 24 hours, so fuel is also a consideration if you use more, less so if you are not maintaining the same living environment while sailing from point to point. Our maximum continuous run time to date has been just over 99 hours.

Like other posters have said, you need to list what you plan on powering and carefully consider how you want to operate. If you have cruised before, you likely know how you want to operate, but if not, you may under or overpower you choice. Although electrical loads are cumulative, they don't all come on at once so you have to apply a "diversity" factor. If you are powering multiple high load devices such as multiple air conditioners and the hot water heater and want to use the microwave, you have a high load factor. You could turn off one AC unit, the hot water heater and run the microwave on a smaller generator than one that has to run al things all at once. Having to manage power is one way to get a smaller unit for weight, but able to manage maybe 80 to 90% of the time. Remember that you spend more cruising time on anchor or at a marina than you do going point to point.

If I could give you one piece of advice that DOES NOT CONSIDER WEIGHT AND STABILITY, I would err on the high rather than the low side. That night when the water temp is 90, it is 90% humidity and you are trying to sleep at anchor has a way of outweighing a lot of the other factors. I would not consider a light, 3600 RPM single cylinder generator. They are not made for long operation and are much louder.




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Old 05-08-2016, 06:21   #13
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Re: How do you choose a GENSET?

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I've been told that you need 6 to 7 time the nominal current to start the compressor
You don't need to power the starting loads with generator capacity.

Power boost inverters will do the trick. A gang of Victron Multipluses would start anything.

You only need to power the constant load.
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Old 05-08-2016, 06:38   #14
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Re: How do you choose a GENSET?

I cannot for the life of me figure out why any sailboat up to 50 ft needs a 9 kw generator. That is both heavy and expensive to buy plus it would be expensive to run. A 9kw unit would probably burn at around 1 1/2 hours/gallon or call it 20 mins/liter.

Its enormous electrical output would only be necessary if you wanted to run the battery charger on bulk and two AC units, all at the same time. It doesn't take a hell of a lot of self control to learn to run the dive compressor and the AC at different times.

A 5 kw unit should be plenty for anyone. On top of that they are cheaper to buy, easier to fit and only burn at around 3 hours/gallon. Any boat without AC really only needs a 3.5 or 4 kw generator. They only burn at around 5 hours/gallon or 70 mins/liter - nice.

I would not recommend either of the two generators named.
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Old 05-08-2016, 06:57   #15
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Re: How do you choose a GENSET?

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I cannot for the life of me figure out why any sailboat up to 50 ft needs a 9 kw generator ...
Generally speaking, standby and prime-rated diesel generator sets are designed to operate between 50 and 85 percent load, while continuous-rated diesel generator sets optimize between 70 and 100 percent load.
Operating diesel generator sets at loads less than 30 percent for extended periods can impact engine life.
Don’t oversize your generator.
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