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-   -   Gen-set vs. engine (http://www.sailnet.com/forums/general-discussion-sailing-related/98497-gen-set-vs-engine.html)

hallucination 04-14-2013 03:54 PM

Gen-set vs. engine
 
I know this post probably falls into the "newbie" category, but this is the first GEN-SET equipped yacht for me. so yes...I am a newbie :)

I have a fischer Panda 4200 for the genny, and a volvo penta 95HP for the main.

What are the pros and cons of using one or the other for ship board systems/charging? The main engine is quite a bit more quiet than the genny, so I am tempted to use the main with the 3000w inverter for (be easy on me here) the wife's hairdryer, coffee maker and blender. And save the Genny for when AC is absolutely really needed.

I suspect that they both will only last a certain amount of time and cost 4 times as much as one would think to fix either one of them. The Panda does seem to be more intricate "in other words, breakable". where as the engine is much more "industrial"

I have not had time to really see fuel use at idle for the main, vs fuel use at 3000 watts with the genny.

Zanshin 04-14-2013 04:04 PM

Re: Gen-set vs. engine
 
Diesel engines like to be run under load and generally should not be run with little-to-no load. Using your main engine to charge the bank will only use a portion of the engine capacity. 3000W equates to 250A at 12V, even if your alternator could supply that you would need to rev the main engine up in order to produce that - using a purpose-built generator instead of the main engine makes sense. A 4200, derated for real-life temperatures, will produce enough to charge the batteries at 80Amps while the hairdryer is going.
I've got a Victron charger/inverter which would perhaps also make sense for your boat. The unit will give a "power boost" off the inverter if necessary. Meaning that if the Hairdryer and coffee machine are running while you make margaritas the total load might be 4500Watts, and normally the genset would overload; but the Victon supplies the missing 500 Watts through the batteries and cuts out the loading process until the load goes below a given level.

The Fischer-Panda runs at double-speed, shortening it's life and making it a bit louder, but no other generator can produce as much power in such a small package. The downside is that they tend to malfunction more often and an installation with easy access is important. I had 2 Fischer Pandas, one of which had problems, but now have a Cummins-Onan which is much bigger but hopefully more robust.

The fuel consumption of two engines that are producing the same amount of power depends mainly on the size of the engine, the much bigger main engine will consume a lot more than the Fischer-Panda (mine were miserly fuel consumers).

hallucination 04-14-2013 04:38 PM

Re: Gen-set vs. engine
 
My inclination/mechanical/engineering background tends to steer me towards the same guidance. Engines have a "happy zone", 100hp engines can be unhappy if they are put in a condition where a 85hp is more appropriate. Way back we had a Grey Marine that really had to be propped right or it would get sick.

the main on my boat should be used at 1800-2000RPM, if hair is wet, or the crew is thirsty, fire up the inverter.

If it is party time, and you are wanting "creature comforts" turn on the panda. It is made to make juice, not move the beast.

does everyone concur? or have I thought wrongly

RichH 04-14-2013 06:37 PM

Re: Gen-set vs. engine
 
Piston engine prime movers will run almost indefinitely at 75% of full load rpm.

A low turning engine with no applied load can quickly form a 'glaze' on the cylinder walls.

Rx: Run the smallest HP prime mover at 75% max. rpm.

--------

That stated, Yanmar recently introduced in the EU an integral 'gen-set' that fits between the engine and the transmission .... and will replace independent 'gen sets'. Whats not known is what will happen to a low turning, low loaded prime mover that sits for hours on end at low rpm. The question has to be asked: what did Yanmar do to alleviate the usual 'glaze', etc. problems in a lightly loaded, relatively slow turning engine? These 'were' supposed to show up in the US ... but there's been no 'buzz' about them.

One 04-14-2013 06:38 PM

Re: Gen-set vs. engine
 
Quote:

Originally Posted by hallucination (Post 1016439)
does everyone concur? or have I thought wrongly

Nope, seems like the way to do it. It's the same thing with inverters. I have two inverters on my smallish boat, Both are small, but one is smaller than the other, so I don't have as much "overhead" when only using a little bit of power (charging laptop and running a few leds, for instance).

outbound 04-14-2013 10:14 PM

Re: Gen-set vs. engine
 
Plumbed for a generator but have yet to put one in (need to spread the pain over a few years). Have 2 d400's and solar panels with highout put alternator. Figured would keep me going until moving south or adding watermaker. Wondering about sharing suggestions for diesel gensets. Fischer Panda was on the list until Zanshin's kind post. Hate engine noise and not too keen on wrenching either ( do it but grumble). Thanks.

Zanshin 04-14-2013 10:43 PM

Re: Gen-set vs. engine
 
A lot of the bigger yachts have two gensets, one dimensioned (much) smaller than the other. This is done so that at night the small genset runs to supply the reduced needs, while running at somewhere between 50-75% of load, then the big genset runs during the day when high loads are required and occasionally both will run at peak load times. All this complexity is done so that the engine lifecycle is maximized.

outbound 04-14-2013 10:54 PM

Re: Gen-set vs. engine
 
s/v Z- you seem experienced with gensets. Would you be kind enough to critique the plus/minuses of the major brands used in the setting of a 40-50' cruising/liveaboard boat.

Zanshin 04-15-2013 08:05 AM

Re: Gen-set vs. engine
 
I can't really comment too much on brands I don't know from experience, but here goes my view:

Fischer-Panda generators run at high-speed, for a diesel, and can thus output a lot of power per pound of generator weight or per cubic foot of generator volume. They are often used where space is the major consideration. Their output is a pure sine and they have an optional power-boost for temporary overloads (i.e. cold crank on big electric motors). Due to high speed and loading and some engineering idiosyncrasies such as the use of an aluminum instead of steel mixing elbow, they do need more maintenance than other similarly dimensioned gensets.

Other major players, such as Northern Lights and Onan, run at only half the speed and don't generate as many watts per pound/cubic foot. I have experience with bigger ones, in the 9 to 11KW range, and at that size the engines are no longer small 1-cylinder Farymann (spelling?) or 2-banger Kubota engines and are commensurately more robust.

I think that putting a genset in an existing boat should start with measurement of the dimensions where the generator is to be installed and to see what can fit inside (much of that volume won't be engine but soundproofing housing). Then look where the genset's access is - the impeller is the first thing that comes to mind, then the oil filter/oil change mechanism. If those aren't accessible in your planned installation then go for another brand which is accessible.

outbound 04-15-2013 08:11 AM

Re: Gen-set vs. engine
 
Thanks Z for sharing your thinking. Orginal spec was for Fischer- Panda DC AGT. ? Can you speak to the difference between AC and DC gensets in practical usage terms?


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