Triskel power generation system on Distant Shores III

[Dockhead]

Originally Posted by Kenomac

How do you “limp home” if your diesel engine poops out with something like a broken lift pump or air in the lines, where you’re unable to locate the source? Let’s also assume no wind and an imminent storm approaching, because that’s usually how things go. And you’re in the middle of nowhere wondering why you opted for only one source to charge your battery bank.

Sure, but if your main engine is out, then you've got bigger problems.


A separate generator of one type or another backs up the diesel engine as well as the electrical end. It might be desirable to have a backup for that, for someone like me cruising really remote places and without any solar. But for someone with a large solar installation, and considering how extremely reliable diesel engines are, it might not be necessary.

[a64pilot]

The Hughes 269 and 300 helicopter used belts to drive the main rotor, transmitted I think over 200 HP through eight? Drive belts. We were told it would fly on half of them.

However you need to consider all this money and complexity against say the little Nexgen 3.5 KW for example, I have one so I compare it.
It’s all in cost if you do the install is about $6,000 US, it weighs I think 200 lbs and burns a quart of fuel an hour, and I’m told and I believe it lasts over 5,000 hours, plus as it’s crankshaft is ball bearing and it’s a replaceable wet sleeve, overhaul should be a half day job, honestly.
So if fuel is $4 a gl, operating cost with the purchase price amortized in is $2 an hour.

I don’t care how long you run one or how often, you’ll never spend as much as one of these systems cost.
Now I’m not saying don’t harvest power from your prime mover when it’s running, be foolish not to do so, heck put two school bus alternators on one to do so.

But unless your a power boat that is often motoring, it’s foolish in my opinion to sit there at anchor and run your propulsion engine to make electricity.

[Dockhead]

Originally Posted by a64pilot

The Hughes 269 and 300 helicopter used belts to drive the main rotor, transmitted I think over 200 HP through eight? Drive belts. We were told it would fly on half of them.

However you need to consider all this money and complexity against say the little Nexgen 3.5 KW for example, I have one so I compare it.
It’s all in cost if you do the install is about $6,000 US, it weighs I think 200 lbs and burns a quart of fuel an hour, and I’m told and I believe it lasts over 5,000 hours, plus as it’s crankshaft is ball bearing and it’s a replaceable wet sleeve, overhaul should be a half day job, honestly.
So if fuel is $4 a gl, operating cost with the purchase price amortized in is $2 an hour.

I don’t care how long you run one or how often, you’ll never spend as much as one of these systems cost.
Now I’m not saying don’t harvest power from your prime mover when it’s running, be foolish not to do so, heck put two school bus alternators on one to do so.

But unless your a power boat that is often motoring, it’s foolish in my opinion to sit there at anchor and run your propulsion engine to make electricity.

I like the NexGen very much and I think it could be an ideal emergency backup, to a big alternator on a PTO. It costs 1/3 what my Kohler heavy duty job cost, and weighs 1/4. A very nice unit, it seems to me.

[a64pilot]

A problem you have is there isn’t a PTO on a normal sailboat engine that I know of

[Q Xopa]

Originally Posted by Dockhead

If you look at the curve A64 posted, you'll see that the difference from idle to optimum (which is near torque peak) on his engine is only 6%. My engine is similar, so I think that's typical.


You do make a good point about alternators and cooling, but diesel engines have a narrow enough rev range anyway, so they can generally be geared to be producing good power and flowing decent air from 1000 RPM already. Good alternators (large frame, hot rated) have plenty of cooling and should be cool enough at any RPM. Actually our use case is usually much easier than what schoool bus alternators are designed for -- they are designed to live under a bus hood where on a hot summer day the temps can be over 100C. On my boat, the ER temp never exceeds 30C with the blower on. That's an easy life for a school bus alternator.


See: http://www.prestolite.com/literature...ion_FL1212.pdf

Yes Im sure thats correct for SFCs. Thats suprising. Hardly worth much effort to chase that.

Agreed about pulley ratios.

The only limitation is generally a physical one.

The biggest crank pulley I can squeeze on my 4JH4 without impinging on raw water pumps etc is 7 inches. Most arent that big.

So then it gets down to how small on the Alternator. The smallest 8 groove pulley I could find for my 7/8" shaft large case alt was 2.36".

Really this isnt much pulley circumference to try and drive large amounts of power required to output high amps from. So even with the 8 groove serpentine the belt slip and dust can begin to become an issue.

The smaller the Alt pulley we use to try and speed it up the more we reduce its torque transfer ability.

This works out to be a 3:1 ratio.

My Engine max rated RPM is 3,200.

My Alt max rated RPM is 10k continious and 12k intermittent.

So this has my Alt RPM at 9,600 max eng RPM.

If we were really pushing the limits there could be some more to be had, maybe? But of course the max Alt RPM limits are getting. Published manufacturers limits are often conservative, but the wear rate and reliability will have to suffer.

This is as fast as any other set ups are that Im aware of. Most are not this fast.

However this is only 2,400 Alternator RPM at 800 engine RPMs. Still a lot of under utilised Alternator production not being realised.

Re the N1602 400A 28v "Hummer" Alternators. They are bloody heavy at 112 lbs. I certainly wouldnt fancy braking its fall with my big toe. But not quite 300lbs.

[john61ct]

Originally Posted by a64pilot

A problem you have is there isn’t a PTO on a normal sailboat engine that I know of

We just established (I thought) that there is no need for one?

[john61ct]

Originally Posted by Q Xopa

They are bloody heavy at 112 lbs. I certainly wouldnt fancy braking its fall with my big toe. But not quite 300lbs.

That is a lot lighter. Perhaps the other bit bigger Niehoff units I was looking at weren't for Hummers specifically, or shipping weight specs heavier than installed weight?

Originally Posted by Q Xopa

The biggest crank pulley I can squeeze on my 4JH4 without impinging on raw water pumps etc is 7 inches. Most arent that big.

So then it gets down to how small on the Alternator. The smallest 8 groove pulley I could find for my 7/8" shaft large case alt was 2.36".
…
However this is only 2,400 Alternator RPM at 800 engine RPMs. Still a lot of under utilised Alternator production not being realised.

Eco-Tech specs their high-output amps at 1800rpm, so some headroom there.

But I assume people looking for big-KW output off their propulsion engine are resigned to a lot more installation engineering than the usual bolt-on replacement alt setup.

[Dockhead]

Originally Posted by a64pilot

A problem you have is there isn’t a PTO on a normal sailboat engine that I know of

Indeed, and I don't know how to solve this. The drive system is something which would need to be properly engineered, obviously.


There is a limit to how much power you can take off the front pulleys of small diesel engines; they are specified in Yanmar manuals. These limits are quite far below what would be needed to drive a 10kW alternator.

[a64pilot]

Originally Posted by john61ct

We just established (I thought) that there is no need for one?

I must have missed that.
I don’t know how you could draw a significant amount of power without one, and if your not really drawing a significant amount of power, well then you aren’t accomplishing anything you can’t from alternators, and are not effectively using that big engine.
See, you need within limits to taylor engine size to load, or your not getting your money’s worth out of a big motor.

Of course I still think that the only logical use of the prime mover motor to generate electricity is in an ancillary mode, or it’s running anyway, may as well use it for electricity too.

I think the logic breaks down though for larger scales. It was stated earlier that we are talking upwards of I believe 8 KW, and my opinion is when you get there or larger, it’s more efficient and cost effective etc. to use a separate electrical generation system aka built it genset.

I would start looking at what transmissions there are available that may bolt to a Yanmar that have a PTO, all PTO’s I’m familiar with take power from the transmission.

As far as belt drive, I just remembered, the Nexgen 3.5 and 5.5 KW drive the generators with a single belt, it’s how they can turn the engine at 2800 and the generator at 3600. They say that is Patented, I don’t see how, but that is their claim.

[Q Xopa]

Yes the Ecotechs are nice units.

But they are also not cheap. At 1,987 for 200A 28V.

In comparison my poor little large frame, (school bus type) 110A 28V at $258

Okay it's only half the output but I can buy 7 for the price of one.

I'm not sure the Ecotechs are 3 times better or last 3 times longer.

[tanglewood]

Originally Posted by Dockhead

Indeed, and I don't know how to solve this. The drive system is something which would need to be properly engineered, obviously.


There is a limit to how much power you can take off the front pulleys of small diesel engines; they are specified in Yanmar manuals. These limits are quite far below what would be needed to drive a 10kW alternator.

I looked into this quite a bit when putting together our next boat. As you say, the engine manufacturers specify load limits on drive pulleys. It’s typically some combination of HP and side load on the crank end. So the smaller the engine, the smaller the alternator that would be allowed. Somewhere back I mentioned 10% of engine rated power as the approx limit.

The other limit is the drive system, and those are typically belts. I run a full model of the belt drive system for our boat using Gates’s design tools. I was quite surprised by the results for a multi rib (serpentine) belt. They can transmit a LOT of power with very little power loss. The belt loading passed with flying colors.

I also looked into PTO driven alternators. They are out there, but pretty rare. One of the challenges is that a PTO typically runs at engine RPM, and alternator belt drives step up the alternator speed around 3:1. To get that, you need a gear box between the PTO and alternator, and that gets expensive. Or you can run the alternator slower, but then it gets bigger.

Given all this, it’s not a surprise that alternators are set up the way they are, and that big alternators appear more regularly on larger boats.

[Dockhead]

Originally Posted by tanglewood

I looked into this quite a bit when putting together our next boat. As you say, the engine manufacturers specify load limits on drive pulleys. It’s typically some combination of HP and side load on the crank end. So the smaller the engine, the smaller the alternator that would be allowed. Somewhere back I mentioned 10% of engine rated power as the approx limit.

The other limit is the drive system, and those are typically belts. I run a full model of the belt drive system for our boat using Gates’s design tools. I was quite surprised by the results for a multi rib (serpentine) belt. They can transmit a LOT of power with very little power loss. The belt loading passed with flying colors.

I also looked into PTO driven alternators. They are out there, but pretty rare. One of the challenges is that a PTO typically runs at engine RPM, and alternator belt drives step up the alternator speed around 3:1. To get that, you need a gear box between the PTO and alternator, and that gets expensive. Or you can run the alternator slower, but then it gets bigger.

Given all this, it’s not a surprise that alternators are set up the way they are, and that big alternators appear more regularly on larger boats.

PTO doesn't need to come out of the gearbox. I have seen a PTO on a main engines which was based on a jackshaft in two pillow blocks, connected to a flange bolted onto the front of the crankshaft with a drive shaft with two CV joints. That was on a large commercial fishing boat, and it would take quite a bit of space, but on a new build you might manage something like that.


The drive would eat some power, and all that gear wears when being turned, so I would think a clutch would be desirable.


Whether such a contraption would be worthwhile is a different question.


Perhaps toothed belts would be more realistic, or perhaps two identical large alternators on opposite sides, so that the belt tension cancels out. Two of the large Leece Neville alternators could produce something like 8 or 9 kW.


I don't know, however, how much of the PTO limit relates to side loading on the crank, and how much to some other factor. I guess Yanmar don't want us overloading the engines by eating up the headroom, either.


I think a real engineer would be required to figure this out properly.

[tanglewood]

Originally Posted by Dockhead

PTO doesn't need to come out of the gearbox. I have seen a PTO on a main engines which was based on a jackshaft in two pillow blocks, connected to a flange bolted onto the front of the crankshaft with a drive shaft with two CV joints. That was on a large commercial fishing boat, and it would take quite a bit of space, but on a new build you might manage something like that.


The drive would eat some power, and all that gear wears when being turned, so I would think a clutch would be desirable.


Whether such a contraption would be worthwhile is a different question.


Perhaps toothed belts would be more realistic, or perhaps two identical large alternators on opposite sides, so that the belt tension cancels out. Two of the large Leece Neville alternators could produce something like 8 or 9 kW.


I don't know, however, how much of the PTO limit relates to side loading on the crank, and how much to some other factor. I guess Yanmar don't want us overloading the engines by eating up the headroom, either.


I think a real engineer would be required to figure this out properly.

Yes, lots of ways to do it if cost and effort are no objective. Larger engines have SAE A, B, and C PTOs on the engine itself, and of course many gears have PTO pads as well - even clutched PTOs. We have a clutched gear PTO for hydraulics. The clutch is there not to reduce wear, but to shut down and disconnect the hydraulics in case of a failure.

[Colin A]

Originally Posted by Dockhead

PTO doesn't need to come out of the gearbox. I have seen a PTO on a main engines which was based on a jackshaft in two pillow blocks, connected to a flange bolted onto the front of the crankshaft with a drive shaft with two CV joints. That was on a large commercial fishing boat, and it would take quite a bit of space, but on a new build you might manage something like that.


The drive would eat some power, and all that gear wears when being turned, so I would think a clutch would be desirable.


Whether such a contraption would be worthwhile is a different question.


Perhaps toothed belts would be more realistic, or perhaps two identical large alternators on opposite sides, so that the belt tension cancels out. Two of the large Leece Neville alternators could produce something like 8 or 9 kW.


I don't know, however, how much of the PTO limit relates to side loading on the crank, and how much to some other factor. I guess Yanmar don't want us overloading the engines by eating up the headroom, either.


I think a real engineer would be required to figure this out properly.

There are several manf of PTO's for the marine market that make ones that bolt to the front of the engine with pillow blocks. It's some what common on smaller work boats like fishing and lobster boats. https://loganclutch.com/marine-applications
The smallest engine I have seen one on was a 40 or 50 hp westerbeke.

[Dockhead]

Originally Posted by Colin A

There are several manf of PTO's for the marine market that make ones that bolt to the front of the engine with pillow blocks. It's some what common on smaller work boats like fishing and lobster boats. https://loganclutch.com/marine-applications
The smallest engine I have seen one on was a 40 or 50 hp westerbeke.

That's very much like the one I saw, the one under "front mounted PTO's".



That would deal with the side load issues, but are there other issues taking lots of power off the front of the crankshaft?