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Old 15-01-2013, 06:49   #16
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Re: Generator off the main engine possible?

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Originally Posted by x-ray View Post
And always remember, that a big alternator will apply big loads on the belts.
This may give you trouble, while manouvering, i.e. when changing from
forward into reverse gear, cause when doing so, you need low revs in order to keep the gearbox alive, but low revs might not be enough to withstand the load of the alternator(s), and the engine will stop....
Regards
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In addition, be sure to check the side-load rating on the engine crank bearings. You'll quickly need an engine rebuild of the lower end if you put too much or the wrong side-load on the crank.
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Old 15-01-2013, 07:05   #17
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Re: Generator off the main engine possible?

I always advise against using your main engine for a generator. The main engine is an expensive part of your boat and you need it for moving the boat. Running it to produce AC power will add hours and shorten the life of the engine, requiring replacement or rebuild sooner. The OP has a trawler I see no reason not to install a generator. This will save ware and tear on the main engine. Also hanging high torque loads on the front of the crank can place loads that the engine was not designed for. Just because you can do something does not always make it a good idea.
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Old 15-01-2013, 20:36   #18
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Re: Generator off the main engine possible?

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Good God, Lloyd, what are you doing with all that power?! Making steel on board?

Is that DC or AC power? If it's DC power you won't have any problem synching them-- just dump it all onto a common bus and the inverter (or in this case, gang of paralleled inverters) will sort it out.

If it's AC power, then you are in for some commercial power generating type control systems, costing probably millions.
Dock....d

I'm the design consultant...it's a fish boat actually a fleet of boats.

Man I can't even imagine one 100kw DC generator let alone 2.

The system is as follows;

Gen1 480 volt 3 phase 100kw, Hydraulic motor drive from the propulsion engine.

Gen2 480 volt 3 phase 100kw, Hydraulic motor drive from the propulsion engine.

Gen3 480 volt 3 phase 100kw, Auxiliary Caterpillar driven.

One Bus for ship loads.

The system has to be auto, as much as possible, the ships engineer is a fisherman 1st.

My job is to create system that can sync Gen1 and Gen2, or Gen1 and Gen3. To share bus loads.

Now on a job like this my biggest issue are loads...power factor, induction, and resistance loads all from the same bus.

I need DVR w/Droop controller, auto sync controller. Speed management.

I wish I could do dc bus to rectifiers, then to inverters...that would be easy.

It's not the case for these kind of loads.

My whole point is Ac gen from a variable speed propulsion can and does make sense/cents for larger yachts.

Lloyd
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Old 16-01-2013, 00:19   #19
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Re: Generator off the main engine possible?

I would not want to be on a boat with an auto-sync controller for three 100KW AC gennies. I would use DC gennies at 480 or 750V -- or rectify the AC gennies with good power electronics. Then use inverters as necessary from the common DC bus.
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Old 17-01-2013, 14:34   #20
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I would not want to be on a boat with an auto-sync controller for three 100KW AC gennies. I would use DC gennies at 480 or 750V -- or rectify the AC gennies with good power electronics. Then use inverters as necessary from the common DC bus.
Auto start and auto sync is absolutely common place with mega watts 3 phase ac in commercial shipping.
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Old 17-01-2013, 14:35   #21
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Re: Generator off the main engine possible?

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Auto start and auto sync is absolutely common place with mega watts 3 phase ac in commercial shipping.
Without engineering officers onboard to look after it?
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Old 17-01-2013, 15:02   #22
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Re: Generator off the main engine possible?

Yes. I have a SeaPower unit on my Yanmar 4JH2E(53hp) and it works great. it can run my 16000btu reverse cycle, microwave, toaster, tv, etc.

Here is a link to their website:

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Old 17-01-2013, 15:04   #23
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Re: Generator off the main engine possible?

Granted with that amount of power there will be engineer officers on board, however I really see no reason not to be using a similar design of software driven switchboard with the 300kw set up discussed. 95% of problems with it will require a simple power cycle to reboot, and any other unsolvable failure manually control the board and sync using simple synch lamps built into the board if budget is tight.

As to the OPs question the only reliable way apart from using DC via inverters as previously stated, in my opinion would be to drive the engine at constant RPM to maintain frequency, and control propeller thrust using pitch controllable blades.
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Old 17-01-2013, 15:23   #24
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Re: Generator off the main engine possible?

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Granted with that amount of power there will be engineer officers on board, however I really see no reason not to be using a similar design of software driven switchboard with the 300kw set up discussed. 95% of problems with it will require a simple power cycle to reboot, and any other unsolvable failure manually control the board and sync using simple synch lamps built into the board if budget is tight.

As to the OPs question the only reliable way apart from using DC via inverters as previously stated, in my opinion would be to drive the engine at constant RPM to maintain frequency, and control propeller thrust using pitch controllable blades.
The problem with syncing AC is that one has to worry about voltage, phase angle, and the first derivative of the phase angle. Mis-syncing AC can be quite spectacular. Syncing DC only involves worrying about the voltage. This is one of the reasons why navies are switching from AC to DC. See this paper, for example.
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Old 17-01-2013, 15:51   #25
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Re: Generator off the main engine possible?

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The problem with syncing AC is that one has to worry about voltage, phase angle, and the first derivative of the phase angle. Mis-syncing AC can be quite spectacular. Syncing DC only involves worrying about the voltage. This is one of the reasons why navies are switching from AC to DC. See this paper, for example.
Interesting paper. I absolutely agree with what you say above, which is why I would go with an automated system, and if manual sync was such a massive concern you could even have a split bus arrangement and have access to 2/3 your power with out even having to think of syncing for emergency use. I personally think this system would be simpler and more reliable than the additional equipment required to invert from DC in the circumstances discussed.
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Old 17-01-2013, 19:20   #26
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Re: Generator off the main engine possible?

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Originally Posted by Tim R. View Post
Yes. I have a SeaPower unit on my Yanmar 4JH2E(53hp) and it works great. it can run my 16000btu reverse cycle, microwave, toaster, tv, etc.

Here is a link to their website:

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Hi Tim,

I have been looking at the 4KW SeaPower unit to provide AC power when cruising. I operate my boat from the pilothouse in a pretty hot climate and presently use a 4KW Kohler generator to power the 16K BTU of air conditioning. Most of the time I am away from my slip, I am under power. Boomarang is a full displacement trawler with a Yanmar 4JH3E (56HP) diesel, and is actually over-powered by about 20HP.

I was in the initial planning stages of a system comprised of a large DC alternator and AC inverter/charger.

A cruising generator seems much simpler and ideal for the way I use the boat. Shore power in the slip, SeaPower underway and the Kohler at anchor. It would actually load the Yanmar more favorably toward the 85% recommended cruise power. I would be very interested in hearing about your experience with SeaPower. Especially size, price, reliability etc.

Many thanks for anything you can share.
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Old 18-01-2013, 12:52   #27
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Re: Generator off the main engine possible?

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Hi Tim,

I have been looking at the 4KW SeaPower unit to provide AC power when cruising. I operate my boat from the pilothouse in a pretty hot climate and presently use a 4KW Kohler generator to power the 16K BTU of air conditioning. Most of the time I am away from my slip, I am under power. Boomarang is a full displacement trawler with a Yanmar 4JH3E (56HP) diesel, and is actually over-powered by about 20HP.

I was in the initial planning stages of a system comprised of a large DC alternator and AC inverter/charger.

A cruising generator seems much simpler and ideal for the way I use the boat. Shore power in the slip, SeaPower underway and the Kohler at anchor. It would actually load the Yanmar more favorably toward the 85% recommended cruise power. I would be very interested in hearing about your experience with SeaPower. Especially size, price, reliability etc.

Many thanks for anything you can share.
Email sent
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Old 29-01-2013, 19:23   #28
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Re: Generator off the main engine possible?

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The problem with syncing AC is that one has to worry about voltage, phase angle, and the first derivative of the phase angle. Mis-syncing AC can be quite spectacular. Syncing DC only involves worrying about the voltage. This is one of the reasons why navies are switching from AC to DC. See this paper, for example.
Those worries are long gone with today's controllers. Both Bassler and Selco make controllers that deal with the issues of reactive power, capacitance, PF of different users on the same bus. Along with Digital AVR's on the gens.

While parallel gen-sets won't make much cent's for a small on-board AC Gen-set, as soon as you get into Yacht size 75 feet and up it sure makes a lot of CENTS.

With load sharing you can run 2 smaller gens, so everything is at close to max efficiency. Also gives you the option of shaving when shore power isn't enough.

Variable speed Cruise Gens driven by hydraulic pump, Hyd-motor, and controller are also now scaleable down to 8Kw. So for motor yachts there is efficiency to be had to the tune of 2-6 gallons per hr, by not having the auxiliary gen-set run while underway.

Lloyd
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Old 29-01-2013, 21:15   #29
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Re: Generator off the main engine possible?

As others have said, automatic paralleling of multiple Gens and load sharing is common on larger vessels and I use it all the time on Super-yachts
Paralleling Operation in Marine & Offshore control technology | DEIF A/S
They work flawlessly if designed right and are suitable for class UMS engine rooms.
I need thruster or anchor windlass?? press a demand button on bridge and 2nd or 3rd Gen automatically starts, ramps up and shares load. When finished clear demand and you are back to hotel loads on less Gens.

However, we are not SY’s and that level of automation is too expensive to consider

For or simple cruising boats I am firmly in Dockhead’s camp that we use our house bank as a load buffer and create DC charging from a variety of sources.

SG did at one time have a Main Engine A/C Generator installed, but according to the Australian Captain who sold me the boat….. they could never get the Cycles to stabilize, so installed a 12Kva Northern Lights
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Old 29-01-2013, 22:18   #30
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Re: Generator off the main engine possible?

There are a great many Large DC Alternators used around the wrecking yards from GM large truck, ambulances, small diesel equipment ect! The GM ones are in plus 100 amp alts with internal regulaters! if your engine will pull one you can make all the dc you could need if ya have big battery banks, and a big inverter you can use and replace quickly with a set up like this ! Ive used them for a long time, and they worked well for us ! just a thought from an old cheap guy !
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