Use Main Engine as Generator-idling

[a64pilot]

The cost of using your propulsion engine to generate power isn't fuel, that's trivial. It's wear and tear on the engine.
If you assume an engine cost $25,000, a number I've seen here a few times, and you assume max life expectancy is 5,000 hours, then right there just replacement cost of the engine is $5 an hour. Add fuel, maintenance etc and it might be as much as $8 to $10 an hour, maybe lower if fuel is cheap and you do your own maintenance, but no matter how you look at it, it ain't cheap.
I bought left over panels from an installer for .50c a watt, and that with wiring, Outback 80 and a mount I built myself, I'll have initially 750 W for about a grand or about 120 hours of running my main engine to make power, after that it's free.
Now with my 660 amp hr bank of AGM's it takes I believe about 5 or 6 hours to recharge them daily to 100%, not fully recharging them will shorten very expensive batteries life, so I would be running my main engine a lot. That is at least 35 hours a week, so in a month the Solar has paid for itself and past that it's making me money

I can't make the "numbers" work using my propulsion engine to make power, there are other considerations of course, many just couldn't bring themselves to add those nasty looking Solar panels and I can understand that, but from an economic perspective, using the main engine just gets expensive, fast.

[Cheechako]

I think it's harder to calculate than that. There's a cost to not running your main engine also. Many fail prematurely from lack of use. If you can run your engine everyday, that may be a good thing. Large generators that are run continually may go 30,000 hours.... or a lt more. Just sayin... it's complex. Using a simple main engine for recharging avoids the clutter and cost of solar panels, arches or frames to support them etc. :>)

[Dockhead]

Originally Posted by Cheechako

I think it's harder to calculate than that. There's a cost to not running your main engine also. Many fail prematurely from lack of use. If you can run your engine everyday, that may be a good thing. Large generators that are run continually may go 30,000 hours.... or a lt more. Just sayin... it's complex. Using a simple main engine for recharging avoids the clutter and cost of solar panels, arches or frames to support them etc. :>)

Exactly. You need to calculate the marginal cost of this use of the main engine, which is the difference in what you would spend if you use it for this and what you would spend if you don't.

I think very few sailboat engines, other than on charter boats, get timed out on hours within any economically meaningful time, so I think you can forget hours on the engine.

If it replaces a separate generator, I am certain that it will be cheaper to use the main engine because its a more efficient use of that resource.

If I had a cat, I would definitely be using one (or both) of the mains with a humongous alternator, rather than having a third diesel engine on board.

I don't see anything wrong with this idea but one should take care to put a reasonable load on the engine. The alternator (and the bank it's charging) should be large enough.

This would work really well with LiFePo batts, by the way, which have large charge acceptance and no need for absorption phase. In fact I think with LiFePo batts you probably really have no need at all for a separate generator, if you can arrange a huge alternator, maybe a third, direct-drive one which can really use the main engine efficiently.

Some people I know who do this put the engine in gear when they are charging lightly (in absorption phase), to keep some load on the engine. That's wear and tear on the gearbox, shaft seal, cutless, etc., but maybe worthwhile if the load is really light.

[BobH260]

I agree it is a complicated calculation.

I think the engines that fail with low hours probably were only used to get the sailboat out of the slip and back in, never got warmed up. Often results in condensation if the oil never goes above 160*, especially in cooler climates.

A good compromise is a large alternator and AGM batteries as they will accept twice the current of flooded cells and so greatly reduce the engine running time. Then use a smaller solar panel for the absorption charge and float once the engine gets the bulk charging done. I don't think it is practical to bring a battery up to 100% with an engine unless you are motoring for the day anyways.

The solar cell greatly extends the life of the batteries. I use a trickle charger on motorcycle batteries whenever the bike is parked in the garage. Doing this results in batteries that last me 4 years instead of 2. I think on a boat that is another big advantage of a solar panel.

Bob

[a64pilot]

You know, I don't know all that many people that cruise really, but for those that do full time, I don't think not running their engine frequently enough to prevent damage is an issue, that's the folks whose boats sit at a dock for months or maybe even years and not move.
If anything I use mine more than I want, and I'm not full time yet.

Now for an on board generator, I think I remember I paid about $5K for my Nexgen, if it lasts for 5,000 hours, then replacement cost is $1 an hour or 1/5th the cost of the main engine. May not last that long, I don't know really, I haven't met anyone who has worn one out, yet. But, I haven't met many that have them either so I have no idea really, but whatever it is, it's less than a main engine per hour.

Solar panels are pretty much a fixed cost, that is barring damage etc. their cost is the same whether they are used or not, the more they are used, the cheaper they become.

I think it seems pretty simple, the weekend sailor who occasionally gets a week or two off for little short trips but other than that is stuck to weekends (me for instance), using the main to provide power makes perfect sense, after all he only needs to do that for a couple of weeks a year, but for the person who lives on and cruises their boat, (me soon I hope) then they need daily power, 365 days a year for years. These people using their main engine to provide power doesn't make as much sense as it does for the occasional user.

Using the main is cheap to start with, but expensive if used extensively, Solar is high to start with, but pretty much free until it hits it's life limit, however long that is.

Now don't get me wrong, I have a big 150 amp Alternator myself, an on-board generator and Solar panels and of course shorepower, and a Honda as standby, actually two but I'll probably sell one. My plan is to get as much power as I can from any available source, but hopefully never to use my main engine solely to provide power.

Then many will tell you that pulling high power from an alternator at lower RPM's is bad on the alternator as it's air cooled and at low RPM, not much cooling, plus from years of engine experience I know that not loading a Diesel and running it at relatively low RPM will shorten it's life, look up wet stacking and bore glazing, plus oil temp doesn't get high enough to cook off the moisture that builds up in it. Lower RPM, lower temp operation of a Diesel is harder on it that running it at 65% to 75% load is.

[shakey doug]

I have not checked all previous posts so this may have been covered.

If your Main is a 2 stroke they hate long periods of low rev soft running they can and do Glaze to point where honing is the only cure, some Bushies use Acme part number 123-abc [ Ajax Powder. for a quick cure.

The life of the transmission drive plate is greatly reduced due to Torsional oscillation. Reciprocating engines rotate in a series of jerks, worse at low speed not smoothly as seen by the Human eye.

Some makes of Transmissions cannot be run for long periods in reverse as this side of the circuit uses needle rollers not balls as used in Fwd.

[stefano_ita]

a64pilot get it

i'm planning using lots of solar power but not very useful in high latitude cruising...so i would need another safety source of energy...having 2 engine, buy a 3 rd is MAYBE a stupid ideas...keep 1 by 1 engine running a bit more than idle to recharge battery...well maybe it could be a nice idea but it has many cons like engine wearing just to produce a pair of kw...

does according to you a not marine generator, a cheap 1000 dollar 2,5-3kw generator can be fitted in the engine room without overheat everythings?

engine room will be keep cooled with 1 big blower and 1 big out-blower, and the generator just in front of the outside outlet so all the heat is vacum pushed away?

i hope some1 will understand my english

[BobH260]

Originally Posted by stefano_ita

a64pilot get it

i'm planning using lots of solar power but not very useful in high latitude cruising...so i would need another safety source of energy...having 2 engine, buy a 3 rd is MAYBE a stupid ideas...keep 1 by 1 engine running a bit more than idle to recharge battery...well maybe it could be a nice idea but it has many cons like engine wearing just to produce a pair of kw...

does according to you a not marine generator, a cheap 1000 dollar 2,5-3kw generator can be fitted in the engine room without overheat everythings?

engine room will be keep cooled with 1 big blower and 1 big out-blower, and the generator just in front of the outside outlet so all the heat is vacum pushed away?

i hope some1 will understand my english

I don't think running a small generator inside the boat is a healthy idea. Many cruisers buy a Honda EU2000 generator and run it every day on the swim platform or foredeck to top up their batteries. Get some CO alarms in the boat. You might be surprised how much power you will get out of your panels.
Bob

[stefano_ita]

Originally Posted by BobH260

I don't think running a small generator inside the boat is a healthy idea. Many cruisers buy a Honda EU2000 generator and run it every day on the swim platform or foredeck to top up their batteries. Get some CO alarms in the boat. You might be surprised how much power you will get out of your panels.
Bob

mh.

with the gen exhaust connected to the main dry exhaust? and the engine room completely sealed from the rest of the boat?

co2 and fire alarm were already planned even a camera inside the engine room

[BobH260]

Originally Posted by stefano_ita

mh.

with the gen exhaust connected to the main dry exhaust? and the engine room completely sealed from the rest of the boat?

co2 and fire alarm were already planned even a camera inside the engine room

What does your insurance company say about it ? Would this generator be gasoline ?
The Honda is such an easy proven solution. You maybe trying to reinvent the wheel

Bob

[stefano_ita]

Originally Posted by BobH260

What does your insurance company say about it ? Would this generator be gasoline ?
The Honda is such an easy proven solution. You maybe trying to reinvent the wheel

Bob

nothings, i don't have a boat...yet

maybe yes...in case i get dirty diesel and both of the engine stops..another diesel gen would be unusefull...

reinvent the wheel means? getting new idea or reinvent the wheel of one engine to add another alternator?

[Dockhead]

Originally Posted by a64pilot

The cost of using your propulsion engine to generate power isn't fuel, that's trivial. It's wear and tear on the engine.
If you assume an engine cost $25,000, a number I've seen here a few times, and you assume max life expectancy is 5,000 hours, then right there just replacement cost of the engine is $5 an hour. Add fuel, maintenance etc and it might be as much as $8 to $10 an hour, maybe lower if fuel is cheap and you do your own maintenance, but no matter how you look at it, it ain't cheap.
I bought left over panels from an installer for .50c a watt, and that with wiring, Outback 80 and a mount I built myself, I'll have initially 750 W for about a grand or about 120 hours of running my main engine to make power, after that it's free.
Now with my 660 amp hr bank of AGM's it takes I believe about 5 or 6 hours to recharge them daily to 100%, not fully recharging them will shorten very expensive batteries life, so I would be running my main engine a lot. That is at least 35 hours a week, so in a month the Solar has paid for itself and past that it's making me money

I can't make the "numbers" work using my propulsion engine to make power, there are other considerations of course, many just couldn't bring themselves to add those nasty looking Solar panels and I can understand that, but from an economic perspective, using the main engine just gets expensive, fast.

From a purely economic point of view, you will come out far ahead using the main engine instead of a separate generator, unless possibly your boat is in charter racking up thousands of hours every year, and maybe not even then.

That's because of the concept of "marginal cost". In short, not every hour of use costs you the same. Why not? Because you have a large capital cost to begin with for each machine, and you are paying amortization of that cost every year whether or not you are using up the hours of useful life. So you don't gain anything by spreading the hours over two machines.

The exception might be the case where you are wearing out your machines strictly by hours, because you are using so many hours, AND if the generator cost per hour is significantly less than the main engine. But only in a really extreme case would you actually come out ahead like that because of -- the time value of money.

So for 99% of cruisers, the marginal cost of more engine hours per years is practically zero except only for fuel cost. Even maintenance cost -- at the intensity of use we have -- is more time related than hours related. To put it another way: You've already spent $20k (or whatever) on the main engine, and you are spending $x on maintenance every year and $1000 a year on amortization. Whether you use it 250 hours a year, or 350 hours a year, makes practically no difference in your cost, other than fuel.

Let's say the economically useful life of and engine or genset is 20 years or 8,000 hours. Let's say you need 250 hours a year (my actual usage spending 12 months a year on the boat) and 100 hours a year of generator use, you will not reach the hours limit before they have lived out their economic lives. It's true that some people use their engines more than 20 years, but after 20 years you have to say that they are written off. Even if you can still get some use out of them, the value of that from the point of view of today is equal to scrap value, and it hardly matters anyway because of the time value of money.

So -- to make a long story short -- it is a lot more economically effective to use a single machine for both electrical power and propulsion, IF you can do it without damaging the engine (if the load is matched to the engine, and the engine characteristics are such that you don't get bore glazing or wet stacking).

You do, however, lose the advantage of redundancy. I am not planning to throw away my generator any time soon. But you pay dearly for that redundancy -- no way is it a winning formula economically.

I think the ideal setup would be two diesel engines, one smaller, one larger -- driving large DC generators, which can be used either for propulsion via an electric motor, or to charge a LiFePo bank. Then you have redundant power sources for propulsion -- something I don't have now -- plus redundant sources of electrical power. And when motoring slowly or motor sailing, you can use the smaller generator with a more efficient load factor. If you ever need a whole lot of power (bashing your way upwind in a storm), you can use both generators.

Would be really nice. But would be pretty expensive. For economic efficiency you can't beat one diesel engine doing everything as proposed by the OP.

[dohenyboy]

This Indian car that just came out with a 551 cc diesel engine has a PTO on the differential which you can use, with an optional shaft and generator head, to produce 3kW. with space forward of the engine you could do the same, inline with the crank. 551 cc is about the same size as the Beta 16.

You can get a Beta engine with their Travel Power option and 3.5 kW generated by three alternators. You get two in one.
Seagoing Alternator Options - Beta Marine

I think the Beta engine PTO is designed so you can have 2 175 amp alternators and the 70 amp. that is 420 amps times 12 or right about 3.5 kW. that would be the way to go.
I heard there is a yanmar with a generator head between the engine and the shaft or on the shaft.


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