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Old 09-09-2016, 13:58   #1
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Generator Replacement Thoughts?

I've read so many threads here on this and learned a lot. Thanks to all who have contributed. I wanted to provide the variables (boat, geography, intended use, machinery types) I'm faced with to get some thoughts:

Boat: 42 ft Monohull sailboat

Geography: Chesapeake Bay

Intended Use: ~10 trips ranging from 2-5 days in length per season


-Marineair 12kBTU A/C (~10A running; ~16 to start). Cools owners cabin (fwd) and salon. Two aft cabins have no A/C. Would need a second unit to do that (if we cared enough)
-Seafrost ED / AC fridge / freeze (~5A running)
-Water Heater
-Freedom 1500 inverter / charger
-Lights / nav / stereo / iPads / fans
-Main engine w/ 150 alternator & ED fridge/freeze compressor
-600 AH AGM batteries

Current Generator: 20+ year-old Fischer Panda with one-lung raw-water cooled Faryman engine. Questionable past maintenance. Rehabbed by knowledgeable local guy, but just not up to the task and totally unreliable for our usage. It would probably reliably charge our batteries and run the fridge. Adding an A/C requirement kills it. When it did work, it was nice and quiet with the gas separator.

Discussion: We are glorified weekend warriors. We take a couple of trips a month, wanting to stay on anchor 2-5 days at a time. The Chesapeake is brutally HOT during the summer, often with no breeze. We used to anchor w/o A/C on our past two boats. Can't do it anymore. For those of you in Florida, I used to spend summers there and I think we might have it worse than you. Bay water temp gets to the mid-80s and air can be mid-90s. FP provides a disclaimer that says their output is measured at like, 60-degree air / water.

Our intended use would be, Day 1 sail to wherever, drop anchor and stay 2-3 days. We would want the generator for a/c, fridge/freeze, and charging power during those times. Water heater too at times, although hot water, charging and supplemental fridge/freeze can be obtained off the main engine if needed. If we ever went North in summer or South in winter, I'm pretty sure our actual generator need would decline from summer on the Ches.


Portable: Would prefer to replace with built-in after considering the ad-nauseum discussed pros-cons of portables.

Northern Lights: Would love, but cost is significant, especially since surgery would be required to accommodate it (if even possible). Weight also concerns me.

Mid-RPM: Both FP and Nextgen build freshwater 2,800 RPM units intended to be more robust than the 3600 RPM one-lungers. The FP unit is expensive and people are still complaining about them, so I'm leaning Nextgen, either 3.5 or 5.5 KW. The 3.5 will fit right in. Looks like the 5.5 will just fit with room to service.


- Is my intended use what one would consider "continuous use" or "standby use"? It might be continuous while we're on the boat, but that would only be 4-7 days out of a month? I ask because I've heard people say the compact units by FP & Nextgen are not meant for "continuous use" like the 1800 RPMs are. I guess I'm trying to get at, will one of the compact units reliably do what I'm asking of it? I'm happy to load manage - for instance I only need hot water at shower time and I could run the engine to get that. Likewise, the fridge/freeze is a holding plate system, so that can be cycled and / or boosted with the engine. Battery charger can be cycled and / or supplemented with engine too. Maybe I could even give the A/C a break when we take off to go into town / tour on the dinghy, etc. Of course, while that happens the temp on the boat will skyrocket, so I'm not sure how I feel about that. If you go out playing about in your bathing suit for a few hours, in that heat, it's sometimes important to come back to an already-cooled boat.
- Is there a panel for the NextGen that could tell me how hard it's working (coolant temp, oil temp, etc)? That's one of the problems with my current FP - you turn it on, but you have no idea whether it's totally overworked until it tells you - by melting down in a pile of molten lava...and then you're entire day's travel from home (and typically the local marinas are all full).
- Finally, what would you suggest for this intended use?
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Old 12-09-2016, 10:13   #2
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Re: Generator Replacement Thoughts?

I can't seem to figure out how to edit my original post. Over the weekend I thought about it, and, the total number of trips would probably be more 7-ish than 10, if for no other reason than some of those trips will entail landlubbers more comfortable on a dock and / or social events organized around a marina.
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Old 12-09-2016, 10:34   #3
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Re: Generator Replacement Thoughts?

The NexGen gensets have a good reputation, and for whatever little this may be worth -- I certainly like the looks of them -- simple and robust.

First of all let's talk about measuring and regulating the load on the genset.

To see what % of max load you are putting on the genset, it is elementary to put in an AC voltmeter/ammeter. I have two of them -- one to measure AC power coming into the boat (from shore of genset); one to measure AC power being consumed. They are very inexpensive and easy to install since they use Hall effect sensors.

There's one problem solved -- how to KNOW how much you are loading it.

Now on to controlling the load:

Modern charger/inverters (Mastervolt, Victron, etc.) have all AC power routed through them, and can boost generator (and shore) power to deal with short-term loads beyond the generator's capacity. You can set the maximum amps you want to take from the genset, and the charger/inverter will first taper down the charging, in order to prevent exceeding this, and then start pulling power back out of the batts to supplement the genset or shore power.

This can completely prevent overloading the generator, and you can set this some percent below the rated maximum capacity of the generator to protect the generator even more.

This also has the great advantage that the inverter can cover startup loads from electric motors -- like your AC starting up -- and allow you to use a smaller generator, loaded up more efficiently, than would otherwise work.

If you can fit (and afford) a heavy duty genset (and you might look at Onan and Kohler besides just NL), they are great things -- quiet and smooth and very long lasting. But if you can't -- everyone I know with a NexGen likes it (that doesn't prove anything, but it's a few data points).

I would, personally, avoid FP like the plague. They are everything you don't want a genset to be -- complicated, overstressed, badly engineered, and therefore notoriously unreliable. In my opinion, gensets are things we especially need to be things which "just work", so they need to be simple, robust, understressed, easy to service, well engineered, and well built.

I have a 6.5kW Kohler 1500RPM generator, which is rated to put out 29.5 amps at 220V. I limit the power I take from it to 24 amps to give an extra margin of safety. I am also careful to feed it with lots of fresh, cool air by always running the engine room blowers. That's another thing to pay attention to.

Good luck.
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Old 12-09-2016, 11:10   #4
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Re: Generator Replacement Thoughts?

I think the 5kW Nextgen is the winner. We have 5kW Westerbeke which is very similar technology except direct drive and no belt. We have same loads as you mentioned and we get along fine.

The 3.5kW will be operating near max power a lot if you run AC which is why I would say the 5kW is the better choice.

Some of the fancy inverters with power boost don't work with capacitor regulated generators. The generator waveform is not pure enough in some cases. Some inverter/chargers won't charge from these generators too. The solution is to "trick" the charger by turning on the water heater (or a toaster). That usually cleans up the waveform enough to get the charger running.
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Old 12-09-2016, 11:15   #5
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Re: Generator Replacement Thoughts?

Continuous duty is in my opinion a fishing vessel that goes out for weeks at a time and HAS to have the generator to run the ice plant and puts hundreds or maybe even thousands of hours per year on it. Intermittent is the weekend warrior and or the person that takes an occasional trip.
As far as size of a generator, I think I can make it simple, if you have a single 30 amp shorepower cord, then the Nexgen 3.5 can run anything your shorepower cord can.
If you have a 50 amp shorepower cord, then likely you will want the 5.5 KW.
They both have the same generator, just the 3.5 is engine power limited, it's only a 7 HP motor I believe.
But start looking at your AC ammeter, if your average load isn't much more than 25 amps or so, then the 3.5 will work, if your all over 30, then likely you will want the 5.5 to have some cushion, and if you are over 30, then you will have to have the 5.5 or start limiting what is on at the same time to stay under 30. A 3.5 will make 30, but it's busting its gut to do so. It will make 25 though and be happy.

Now the air hose they come with is the vinyl bilge blower hose, OK I guess if your pushing cold air through it, but we aren't, we are pulling hot air through it, that means it softens up and will collapse easily, and that corrugated hose is similar to corrugated bilge pump hose, it blocks flow greatly, replace it with smooth hose, I used 3" Aircraft Scat hose, smooth bore, high temp silicone that will not collapse, I had overheating issues until I replaced the hose.
I also bought from Nexgen an extra set of engine mounts and used them to mount the enclosure, the generator floats on two sets of mounts and that helps keep it from transmitting vibration into the hull, a lot of noise is actually vibration.
Nexgen parts by comparison are cheap, on another thread someone is faced with having to replace the generator head for their NL Genset at a cost of about $4,000.
The generator head on a Nexgen if bought through them is about $700, can be bought cheaper I'm sure elsewhere, it's a Sincro Series ER .
Now I am not saying a Nexgen is the generator a NL is, it isn't, but it is smaller, lighter and cheaper and does seem to work, and for smaller boats and occasional use, may be all you need.
The Nexgen comes with most everything you need to install, measure how long you want the control cable and order the correct length, other than that you will need hoses for fuel and water and exhaust. It will not charge a battery directly, I hooked into by bank for starting, actually connected to the big engine's starter solenoid.
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Old 12-09-2016, 11:20   #6
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Re: Generator Replacement Thoughts?

Oh, and make the board your going to mount the generator on as solid as you possibly can, you don't want to build a "sounding board" Vibration can / will resonate through the whole boat if it's not a solid mount.
I'm the type that hates putting my head against something solid like a bulkhead and feeling the vibration of the generator, and you don't have to.

On edit, the only thing the control panel tells you is operating hours, nothing else.
The Generator has overtemp and low oil pressure "Murphy" switches. You would have to add oil PSI and water temp gauges if you wanted them.
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Old 12-09-2016, 13:10   #7
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Re: Generator Replacement Thoughts?

Thanks for all that info. Here are some follow-ups:

-I do have AC in, AC out, and DC ammeters installed in my panel, so that's where I'm getting my amp calcs from: I can see the A/C pulling ~10A continuous, another 5 for the fridge / freezer, and close to 10A for the water heater. The Heart inverter / charger oddly does not show through any of myAC ammeters (?). The thought might have been that it has a "powershare" feature which, reading the manual, apparently throttles back the charger to make it play friendly with the remaining AC available after all the other AC gadgets are running. I can see that effect on the DC ammeter (charge current backs off when other AC gadgets kick in). It doesn't appear to have a function that helps start AC motors. I have single 30A shorepower, and I will pop the breaker if I run waterheater, A/C, fridge & charger (unless maybe the charger is in total float mode).

-Are the Victron units' motor starting capabilities in lieu of using something like a Dometic Smart Start, or would that work well in addition, or are the two inconsistent?

-Air supply. I read the Nextgen manual and it talks a lot about airflow and encourages you not to use a sound shield, and A64 noted it too. So, I really want the gen to have a sound shield, as my current FP does. I feel it's necessary. That said, if it's in a sound shield, for either genset, doesn't that mean it's drawing hot, dirty air from inside that case? Wouldn't that be awful hard on the engine? Would it be worth figuring out a way to run air intake hose through the sound shield with minimal noise gain, so as to get cooler / cleaner air to that poor engine?
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Old 12-09-2016, 13:35   #8
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Re: Generator Replacement Thoughts?

Ok likely your inverter charger is like mine, that is power runs through it prior to the panel and therefore prior to the ammeter, so it's invisible to the meter., but of course if it's charging the batteries, it is using power. I run a 16K AC and a 5K AC with a 60 amp battery charger, TVs and all the other stuff and my load is usually about 22 amps, well within the gen limits, but turn on the water heater and I'm over the boats limit of 30 as well as the gen limit.
So if we want to heat water electrically, an AC has to be turned off, same if you want to use the microwave, or toaster, the wife's hair drier etc. Usually though if we want hot water, it is not all that hot outside.
But as I have a 30 amp boat, it is the same as being at a Marina and drawing shore power. If I had a 50 amp generator I could only use a max of 30 without upgrading the boats wiring, something I didn't see as necessary.

Yes the blower does draw air from the sound shield and exhausts it overboard through a hole in the boat that you get to cut. It is drawing in of course cooling air into the shield, if the generator is in a hot environment, then it will be drawing in hot air, mine is in the Lazarette so the air in there isn't hot.

Call them at Nexgen, the guy who answers, will answer your questions. Similar experience as to Rich at Cruise RO.

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