Alternator + Inverter vs Generator

[Dockhead]

Originally Posted by s/v Jedi

Dockhead: what I meant is that a genset even makes sense without A/C in some situations, like spending years at anchor without shore-power and water-hose conveniences. The costs of the genset are less than the extra cost on the main engine in that case..

I haven't run the numbers, but I would bet you dollars to doughnuts that you would never recover the extra cost of a generator. You would use a little less fuel in the gennie compared to the propulsion engine, but same cost per hour of maintenance, and then you have to amortize the whole capital cost of the installation.

A complete generator installation is at least $12,000 which means at least $100/month of amortization, assuming a ten year useful life, not counting the cost of money through time. Add in time value of money and $1,000/year in maintenance and repairs, and you're looking at at least $200/month. If you save two liters an hour (that's being generous) of fuel, and even if your fuel costs $2 a liter ($7.50 a U.S. gallon), you would still have to run your gennie 50 hours a month to make up the difference in fuel cost. Probably more like 100 hours a month, or 1200 hours a year. If you're running your gennie that much, then the premise of a 10-year useful life is blown, so you'll never make it to payback point. I haven't subtracted the extra costs of the main engine for extra hours but that would be peanuts; a few extra oil changes a year and accelerated amortization.

I think the reason to have a generator when you don't absolutely have to have it is simply that it's another fine, expensive, cool toy. It's more pleasing to use, quieter, etc. Nothing wrong with that, if you've got the bucks. But more economical than using the main engine--alternator--inverter, if you could manage that way? No way!

Originally Posted by s/v Jedi

In England you need heating, not A/C ;-).

You got that right. Our boat has the 10kW Eberspaecher heater. It runs on diesel fuel and uses relatively little electricity (batteries cope with it overnight). It would be pretty chilly without it. My favorite trick is to put up the full cockpit enclosure and leave the companionway hatch open to let the heat waft up.

Originally Posted by s/v Jedi

Also note that US washing machines use very little power and you can run them off an inverter easily. The reason is that they don't heat water... you connect them to a hot water supply..

Interesting. Never heard of that type. Our washing machine incorporates a dryer and needs about 1.5kW for an hour or two at a time. Uses a ton of water too. But we love having it on board. It is amazingly useful, more than I ever would have thought. The dryer is perhaps even more important than the washing part. In a pinch you can wash by hand, but getting things dry on board is such a pain. [dodging the spitballs from the "why doncha just buy a condo, you freak?" crowd]

[ViribusUnitis]

Dockhead, your looking at it from the stand point I am as well. I don't have a boat yet, and probably won't for another year. My intention is to sail around the Texas coast, and maybe head for the Carabean at some point. I have little intention to hanging around a marina unless I absoutely have to. Say for putting the boat on the hard or something. I'm expecting around a 40-50 foot boat. My expetation is that I will be a BIG BABY, and require a/c set for the summer, and at night. Sleep at 95F at 90% humidity is miserable. Argue with it all you want, but that is my opinion. My wife says 80F at 90% humidity is miserable. I'm not arguing with her.

1. I'm not really looking to use shore power to power a charger to recharge batteries. That would require sticking around a marina. My intention is to have the boat on a mooring ball, or sailing. Cheaper, and from the where I'm located, closer to my current house.

2. The cost of a gen set is large. Dockhead's math is the way I read it as well. While my costs for the inverter might be low I wasn't looking into a battery charger. The cost of an inverter per W goes down the larger the inverter is. Also, the cost of a modified sine wave, or a true sinewave inverter makes a BIG diffrence in price. Finally, the "inverter/charger" fuction is EXPENSIVE. So for my useage, a high output, modified sinwave unit without the charger fuction should be the lowest cost per W version of an inverter. I've seen suppliers on the internet offering a 5000W unit with up to 10,000W surge for less than $500. I figured surely a quality unit could be found for $1000.

3. I'm still unsure as to why a/c would require a gen set. If the engine is tied to a pair of 150 amp 24V alternators, that's 7200W. Tie that to a 5000W continuous inverter, with a higher "surge" capasity. That would allow the inverter to have a 70% efficency, and still have full 5000W avalible. 5000W is more than a 30 amp 110 shore cord would provide. (30 amp shore cored is a mear 3300W MAX.) In otherwords, it could easily provide enough through put for a a/c set to run. A 16000 BTU unit only requires 1300 W of a/c current.

The other intersting thing about such a large alt. is that that's 10 hp. A 53 hp Perkins engine probably only puts 40 hp out at the shaft. 10 hp would be a 25% load on the engine. That's certanly alought more than just an idle out of a typical sail boat engine.

At least to me, the big hole in my calculation is the cost of installing the system. It would require LARGE alternators installed on the engine, HUGE cables run to the inverter, and then the a/c cables to hanndle the overall draw. Big cables are expensive, it would be VERY important to keep their length short. No idea as to how much such an install would cost, as I don't have a boat to put it in yet. If done correctly, it might well not be that much more expensive than a smaller inverter set. I would expect the labor to install the unit, and get the fitting correct would be more expensive than the cables. And upsizing the cables, while expensive might not end up being that big a diffrence.

[Sailmonkey]

Don't forget that to run a main engine to power an aircond you'll be putting up with heat, noise, etc.. that you would be able to isolate yourself from with a generator.

[hellosailor]

"A complete generator installation is at least $12,000 "
What's that for, a 10-kilowatt Onan with professional installation and plumbing all done at $150/hr by the usual overpaid gen-you-whine retailer??
There are other sources, and the installation is not above any competent sailor.

Then again, you can always buy a Honda AND a RIB, and the nice quiet genset on an extension cord while it vents away from your boat. Still under ten grand.<G>

[ViribusUnitis]

That's actualy a good point about the noise, I didn't think about that.

[s/v Jedi]

I just installed a brand spanking new Northern Lights 6 kW genset. It cost me $7,400 FOB Miami and $80 transport to Panama. Installation $0 because I do everything myself.

We run the genset an avg. of 1,000 hours per year. After 3,500 hours I replaced the injection/exhaust elbow, the injectors and the seals in the raw water pump. After 8 years, total maintenance cost $500. Total cost $8,000.- for 8 years equals $1,000 per year = $85 per month. This is my actual cost after 8 years, not an estimate or something. Also, the genset wasn't junk at that point, it even still ran perfectly, but I could feel that more costly repairs were on the way. So, I removed everything that was in good condition: alternator plus it's external regulator, heat exchanger, starter motor & solenoid, raw water pump, fresh water pump, injection pump, lift pump, AC voltage regulator etc. etc. and put all that away as spare parts because I bought the exact same genset again. I am confident that the cost per month with the new genset will come down to $50 per month.

So, at $1 per hour run-time, you state that you can beat that with the main engine. Well, so be it but I can tell you that you will have a hard time when just looking at the extra fuel burned, double the amount of oil every 200 hours, more expensive filters for fuel & oil, impellers etc. And then, 8 years later, you find that you have 8,000 hours extra on the main engine and it needs an overhaul... there you go, $5,000.- at least. No, all in all I think it will cost you double plus with so many hours on the engine I would feel less confident that it would be ready to save me out of tight situations when needed.

85 hours per month is an avg. of what, 2.5 to 3 hours per day. So, that costs $3 plus a gallon of diesel is $5 per day, giving me 15 kWh plus hot water (water heater is plumbed into the heat exchanger circuit). My batteries are topped up, I can make more than 100 gallons of water daily if I would need to, have a cool boat at night (no need to run A/C during the night, just take the heat of the day out before bed time), rinse my boat with fresh water saving me lots of stainless polishing, run laundry at will etc. I rather spend daily $5 on this luxury than on an extra Cuba Libre in the watering hole. Most cruisers I meet complaining about genset costs spend a lot more in the bar every day!

Last but not least... this isn't a new story, I've been here many times already. Some cruisers sail around the world like crazy (some even in a year) and they never miss a genset or even watermaker. But when you live aboard full time and spend year after year anchored in paradise, sailing from one island to the next, no matter what you say now, you will buy a genset after a year or so or curse your decision to go without one every single day, bulging big black smoke clouds out of the exhaust every time you start the engine etc. But that is just my experience talking, many want to find this out by themselves. ;-)

ciao!
Nick.

[akio.kanemoto]

Originally Posted by s/v Jedi

I just installed a brand spanking new Northern Lights 6 kW genset. It cost me $7,400 FOB Miami and $80 transport to Panama. Installation $0 because I do everything myself.

We run the genset an avg. of 1,000 hours per year. After 3,500 hours I replaced the injection/exhaust elbow, the injectors and the seals in the raw water pump. After 8 years, total maintenance cost $500. Total cost $8,000.- for 8 years equals $1,000 per year = $85 per month. This is my actual cost after 8 years, not an estimate or something. Also, the genset wasn't junk at that point, it even still ran perfectly, but I could feel that more costly repairs were on the way. So, I removed everything that was in good condition: alternator plus it's external regulator, heat exchanger, starter motor & solenoid, raw water pump, fresh water pump, injection pump, lift pump, AC voltage regulator etc. etc. and put all that away as spare parts because I bought the exact same genset again. I am confident that the cost per month with the new genset will come down to $50 per month.

So, at $1 per hour run-time, you state that you can beat that with the main engine. Well, so be it but I can tell you that you will have a hard time when just looking at the extra fuel burned, double the amount of oil every 200 hours, more expensive filters for fuel & oil, impellers etc. And then, 8 years later, you find that you have 8,000 hours extra on the main engine and it needs an overhaul... there you go, $5,000.- at least. No, all in all I think it will cost you double plus with so many hours on the engine I would feel less confident that it would be ready to save me out of tight situations when needed.

85 hours per month is an avg. of what, 2.5 to 3 hours per day. So, that costs $3 plus a gallon of diesel is $5 per day, giving me 15 kWh plus hot water (water heater is plumbed into the heat exchanger circuit). My batteries are topped up, I can make more than 100 gallons of water daily if I would need to, have a cool boat at night (no need to run A/C during the night, just take the heat of the day out before bed time), rinse my boat with fresh water saving me lots of stainless polishing, run laundry at will etc. I rather spend daily $5 on this luxury than on an extra Cuba Libre in the watering hole. Most cruisers I meet complaining about genset costs spend a lot more in the bar every day!

Last but not least... this isn't a new story, I've been here many times already. Some cruisers sail around the world like crazy (some even in a year) and they never miss a genset or even watermaker. But when you live aboard full time and spend year after year anchored in paradise, sailing from one island to the next, no matter what you say now, you will buy a genset after a year or so or curse your decision to go without one every single day, bulging big black smoke clouds out of the exhaust every time you start the engine etc. But that is just my experience talking, many want to find this out by themselves. ;-)

ciao!
Nick.

Hi Nick, I can definitely see the math and logic in your approach here, but turning the situation around a little - what about the math in a smaller boat example with a much smaller main engine.

In my case, my scenario will be very similar to your's - i.e. living at anchor for years... (counting down the months now... whee...) - no marinas. But no A/C.

In my scenario - my boat is too small to take a genset, whether I want/need one or not... and I've spent too much time on this boat to buy a bigger one (or my wife will kill me unless we spend at least 4-5 years on this one as is!) ... anyway.. I digress..

But the key thing here is that my engine is puny compared to the other examples here. 27HP. 3gm30. As per my other alternator mounting thread - I have two switchable 120A alts mounted now (photos coming soon. - and I'm just putting together the mounting for the watermaker HP pump. Without going into the side loading or "enough propulsion power" discussion. In my case, the engine will be quite heavily loaded (engine is happy), and consumes a max of 4L/hour... and the replacement cost of the entire engine (Brand spanking new 3YM30) is only AUD$11000 - (like you, zero installation costs though, I do everything myself).

So do we achieve optimum balance with the alternator/inverter combination where the main engine is actually quite close enough to being a genset size itself and the cost of a new engine isn't that huge?

[negrini]

Lots of rasonable posts say it will depend a lot on how you intend to boat. But from efficiency standpoint, regardles situation, Diesel consumption efficiency in key here. Looking to actual gensets in the market, 5KW gensets demand roughly a 10HP engine, achieved by around 30 cubic inches on displacement that eats around 0.5gph at full load. I doubt your alternator+main engine will achieve same diesel gallons efficiency. A small size engine will surely be more efficient, but far from a dedicated, balanced and matched unity in a genset. That's why nobody take such approach. 1- your alternators will demand a higher rpm on engine to produce same 5KW, it will push you burnt gallons way up. 2- Inverter will pose a big loss per W, even more on cheap unities 3- main engines are not a balanced machinery thus create lots of vibration that will increase the noise on board. 4- you're creating a lot of heat inside your cabin that will drain much more BTUs from AC. 4- you're overusing your main propulsion engine. Take a look at Victron test on genset efficiency conducted somewhere in 2007 (just google it), it's very clear the efficiency points. I run my Honda 2KW to charge batts, microwave, and all other smaller loads on board, takes 14 hours to drain a gallon. When I turn AC on, I must be sure I'm alone at anchor as the little quiet Honda simply scream like a hell, and eats same gallon in just 3.5 hours. I'm installing an Onan.

[s/v Jedi]

Originally Posted by akio.kanemoto

So do we achieve optimum balance with the alternator/inverter combination where the main engine is actually quite close enough to being a genset size itself and the cost of a new engine isn't that huge?

Hi Akio,

Your charging system sounds fabulous and much like our setup. Now, you only need to install a generator ;-)

I say that because no, you have no optimum balance at all. Let's do some math:

you have 2 x 120A alternator. When you take the output of those directly into an inverter, this is what you get: 2 x 120 = 240A @ 13V. That is 3,120W into the inverter which is 95% efficient so you end up with 2,964W. Let's make that 3kW. Now, after 1 hour you have generated 3 kWh of energy at the cost of 4 liters, let's say 1 gallon.
My 6 kW genset: when I run it for 1 hour at full load, I get 6 kWh and consume 0.5 gallon of fuel. That makes the genset 4 times (!!!) as efficient.

Now, let's just say you run that 1,000 hours in a year and I generate at half output so equal power ,also 1,000 hours in that year. You consume 1,000 gallons of diesel while I consume (at 3 kW load 0.35 gallon/h) 350 gallons. The difference is 650 gallons of diesel and now it comes down to the cost of diesel. Here in Panama diesel currently costs $2.63 per gallon so you just lost 650 x 2.63 = $1,700. When you do that 8 years in a row, like we did with our genset, your extra cost is 8 x 1,700 = $13,600. I paid $7,400 for my genset and even if I deduct that, I end up $6,200.- cheaper than you but hold on: you also have 8,000 extra hours on your main engine. And your engine still takes much more oil than a genset (40 oil changes for 8,000 hours means 80 liters extra oil at how much per liter?) more expensive filters, more noise, heat, more expensive replacement parts and the list goes on.
You will never beat a genset because it's like negrini wrote in his post: the genset is tuned in a way that you can never beat with the propulsion engine.

On a 40' boat you can find room for a genset. If not, you can make room. You are on the small side for one but I have seen 36' boats with a genset. Believe me, I had to make room too and make compromises for accessibility even. If all else fails, you can buy a gas-powered Honda generator and still save significantly.

The alternator thing you did is great and it will save the day now and then... it does for us. But I would put the watermaker pump project on hold until you're very sure it's the way you want to do it. Why not couple it to an AC motor and run it through your inverter?? That way, you can always opt for a genset later.

As you now have a 3kW system, you can look into smaller gensets. They will cost less and use less fuel than my 6 kW at half output. They are also much smaller. When you couple it to a Victron 3 kW charger/inverter with their PowerAssist mode, you can still handle 6 kW (3 kW from genset plus 3 kW from inverter... they get added when needed) during peak usage times. Find the Victron document negrini described, it's an eye-opener.

ciao!
Nick.

[Dockhead]

Well, 1,000 hours a year -- my hat's off to you, Nick. You are a serious cruiser. When you get to that very high level of use then of course the economic case for having a generator gets better and better.

Note that I was not arguing against generators at all. I have one, and I'm glad of it. I was merely saying that for 90% of cruisers it will not save money.

The OP has just said that he plans to cruise the Texas coast in summer and stay away from marinas. Well, obviously, he is going to HAVE to have a genset. Running A/C all night is a different regime from charging batteries for a couple of hours.

If I were cruising in 95 degree heat and 100% humidity (yikes!) I would NOT stay away from marinas. The joy of being at anchor is mostly lost if you're shut up below with the genset running somewhere (however well sound isolated) so you might as well be somewhere you can wander around on shore. Not to mention the joy lost by your neighbors at the anchorage. But even for occasional use in such conditions, I think genset and AC are a must.

Concerning the cost of a genset -- a new installation requires a lot more than the genset itself and your own elbow grease. You are confusing the cost of replacing an existing setup with a completely new installation. By the time you fabricate mounts for it, buy and install a fuel system, water lift, exhaust, control system, wiring, switching, etc., etc., etc., etc., no way you an do a decent size 6 -- 7 kW -- genset for much less than $12k and could easily be more.

One more little quibble: I would be careful about advising anyone to buy a 3kW genset. Even with the nifty Victron jobby (a great device; I also plan to buy one) handling your startup surges, you don't want your genset running at 100% just to cover your base AC loads. That's a good way to drive it to an early grave; besides that if you use any other equipment you can quickly get into a deficit spending power budget and run down your batteries. An undersized genset is just a recipe for frustration I think. My generator is a 6.5kW and according to my calculations I will easily load it up to 80% of max without any consideration of toasters, coffee pots, or startup loads.

[s/v Jedi]

Okay, on installation costs:

I don't know much about all the brands, but the Northern Lights genset comes complete with mounts, stainless drip pan etc. You just shove it in there. Also, the control/switch panel is included. You do need a waterlift and some exhaust and fuel hose but a basic installation wouldn't cost more than say $200.- in materials. If you want a primary fuel filter, fiberglass waterlift, shiny exhaust thru-hull etc. it will cost more.

I know about the load... 75-80% load is where I try to be. But the OP now has less than 3kW in theory and I am sure the alternator system will not produce 100% of rated output so a 3 kW would be fine I think... but most in that size are 3,500W anyway.

But I also think that an oversized genset is worse than undersized. We have a really hard time loading up our 6 kW for the break-in period and we're a 64' boat! We even microwave water just to create a load ;-)

I always thought Texas was dry as a bone! ;-)

ciao!
Nick.

[Highlander40]

OK, here is the case for a smaller generator.

My boat is only 40' so weight is important.

After 10 years of use, I have found that different loads occur at different times so average load is very low.

Stove 10A x2
Microwave 10A
Charger about 23A full load,for maybe 10 min. Then ramping down below 10A pretty quick.
AC about 12 A ,same for heat
Refrigeration runs from 12V or inverter.

The generator is a 4.2 KW and puts out 32A continous.

The loads all add up to 55A just dont turn on everthing at once!

The little single cylinder engine is actually quieter than the twin it replaced and changing the oil is a snap, it takes one quart!

[Pblais]

Highlander40,

You make a good case but add an A/C unit and Nick has it beat. Add a watermaker too and it's even better. To avoid a genset you need minimal loads. It can seem cheaper to just use the main engine since the cost of replacement is assumed not to be real. When you use the main engine for charging large amounts it shows up as eventual costs and as Nick's numbers show it's not economical - if you need to make a lot of power.

If you want simple - then eliminate all the big electrical power demands. The more power you demand the more complex the solution. The desire for the cheaper solution is not making more power - it's using less.

Matching the batteries and generator capacity to the real demand is key. Over and under loading both have large penalties. So if you only use your boat for sporadic weekends you really are screwed with large load demands over infrequent periods. You will spend a lot of money up front and not get the full return. It just means the person that buys your boat will need a new engine. It happens. The calendar is an enemy too. Staying home on land in the hot weather has it's costs too. We don't usually attribute them to the cost of the boat but you only have one life and it's all the same money. Owning two homes carries extra costs.

Living aboard makes the numbers show up easily.

[Highlander40]

Pblais,

The second home is a good point, My partner has one and does the 3hr commute from CT to VT and does not use it all the time now. The kids do though. I guess that I'm not that generous.

20 min from work or home and we are on the boat.

I forgot to add the electric hot water heater, 10A. I get the point when you have multiple AC units.

The sequence of bulk charge, cooking, hot water and maybe some AC works well to spread the load while giving the battery bank time to charge fully. By the time we are ready to get off the boat, the house bank is well into float.

We could have built the boat with a second AC unit, there just isn't room for a watermaker as much as I would love to have the freedom.
I can remember a couple of times when we couldn't get water but that is rare. With carefull use we get a week out of our 120 gal water supply.

As far as using the mains for charging? HA! Last time I asked, the replacement cost was about $50K EACH.

One thing that I learned, It really pays to take good care of the genny. With the new unit I plumbed in a T to the raw water inlet so that a hose can be hooked up and flush the heat exchanger out whenever we can. Usually when coming home after a trip.

The most disgusting trend in powerboat design is packing too much s**t into too little OAL. That's not my idea of boating, thats a second home

[Highlander40]

The point was, even with a 4.2KW genny, I am looking for things to turn on and load it up. The time when usage is rationed is very short.