spit balling, AC gen on front of main engine..

[Dockhead]

Originally Posted by a64pilot

That depends, are you an A type or D type? I suspect A type as most are and then yes your overloading it.

I thought you had a school bus alternator?

Type A is all side mounting using belts of whatever type.


Type D is using a front PTO flange and pillow bearings.


Leece Neville school bus alternator is more like 60% efficient so maybe just barely not overloading it. At any rate it's original installation by the Moody works, or rather, by the Yanmar supplier, so I would think it is reasonably engineered.


But I would not install a bigger one.


I think on a new build it might make sense to mount a big Echo Tech or Humvee or similar big alternator off a PTO shaft -- Type D. Maybe the output could be regulated to avoid overloading the engine (see the shape of the curve vs propeller curve).


By the way, I think you have an Autoprop like I do -- note that the propeller curve for these is different and much fatter than that of a fixed pitch prop, leaving at different RPM less headroom for PTO. Worth being careful with.


Perhaps EGT monitoring would be sufficient to avoid overloading the engine.

[Fendell]

Hi All, As the OP I just wanted to say I'm still following the thread closely, and thanks for the constructive conversation.

There seems a lot of engineering to overcome to make this a possibility, which is why I'm guessing its not the norm. I wonder if its not seen more because its not an 'off the shelf' set up?

If there are any aviation buffs watching, is there a down scaled version of a Constant speed drive, similar to the type aircraft use for power generation?

Cheers again

[CassidyNZ]

So it is presumed that the “allowable hp take-off” at the front on the engine is limited because of the smaller size of the crank journal vs the flywheel end?

Originally Posted by a64pilot

Presumably most engines are designed so that the power is extracted from the rear of the crankshaft, if you have ever built engines you’ll remember the rearmost crankshaft bearing is much larger than any of the others.

Then it is said that the “allowable hp” is a linear relationship to RPM.

. . . . the Yanmar installation manual that showed that at max RPM only 8 HP were available to be pulled from the front of the crankshaft and it’s a straight line, so that at 50% of max RPM 4 HP are allowed, that’s 100 amps at 12V.

So presumably the front crank journal grows in size as RPM goes up allowing it to handle more horsepower? Of course it doesn’t so why the hp change? I still don’t get it.

Oh, and by the way, the crank journals on a 4JH engine are all the same size if this clip from the original Yanmar manual is to be believed (only one dimension shown). So that flies in the face of conventional thinking that the front of the crank is less capable of absorbing load than the back one. Yet the manufacturer insists that this is the case.

Maybe the PTO capability at the front of the engine has more to do with the multi-track pulley that sticks out 250mm in front of the engine creating a moment of leverage on the crank journal than it does with journal size. Oh, but wait, Yanmar says that placing devices on either side of the crankshaft centreline does not alleviate the problem!

Too many conflicting arguments here.

[RaymondR]

Originally Posted by Dockhead

Why wouldn't you just use a big DC alternator and invert the power? Vastly simpler and much higher quality power. Eliminates need to keep engine at some exact speed.

Having fiddled with the problem of driving Heavy AC loads for about twenty years now I have come to the conclusion that the big, or multiple, engine driven alternators and a big inverter is the most practicable solution.

High capacity inverters are now readily available and fairly inexpensive and allow a high degree of flexibility in use. Truck, bus and auto DC output alternators are also readily available and a very familiar technology which we need to have anyway to recharge engine start batteries.

If one has the room below or does not mind on deck storage a relatively inexpensive small gas or diesel direct driving a large capacity alternator is fairly easy to implement. I am going this route at the moment with a five hp, electric start, Honda engine and two Bosch Universal 85 amp alternators (I'd go bigger but I already have both engine and alternators) Since the engine is gasoline powered it's going on the deck in an alloy box.

The reason I went with an electric start engine is that I want to be able to start the engine from the galley should I want to use my microwave for more than a few minutes and don't want to have to go on deck on cold, windy or rainy days or especially nights.

The enclosure is being fabricated at a metal work shop as I scribble and I might start a project thread when I return to base from my extant mini cruise.

[CassidyNZ]

Originally Posted by Dockhead

Type A is all side mounting using belts of whatever type.


Type D is using a front PTO flange and pillow bearings.

I once considered a D-type installation but the changing/renewing of belts is a maintenance mission and if one is running more than one device, a multiple belt drive is required even with a D system. Even the standard alt/water pump belt requires stripping the whole setup to renew a belt.

Even with my A-type setup, I have to remove all the belts to replace the standard one but still way easier than a D-type setup.

[skipperpete]

Originally Posted by CassidyNZ

So it is presumed that the “allowable hp take-off” at the front on the engine is limited because of the smaller size of the crank journal vs the flywheel end?







Then it is said that the “allowable hp” is a linear relationship to RPM.







So presumably the front crank journal grows in size as RPM goes up allowing it to handle more horsepower? Of course it doesn’t so why the hp change? I still don’t get it.



Oh, and by the way, the crank journals on a 4JH engine are all the same size if this clip from the original Yanmar manual is to be believed (only one dimension shown). So that flies in the face of conventional thinking that the front of the crank is less capable of absorbing load than the back one. Yet the manufacturer insists that this is the case.



Maybe the PTO capability at the front of the engine has more to do with the multi-track pulley that sticks out 250mm in front of the engine creating a moment of leverage on the crank journal than it does with journal size. Oh, but wait, Yanmar says that placing devices on either side of the crankshaft centreline does not alleviate the problem!



Too many conflicting arguments here.

Not really conflicting , just different points of view on the same question. The front pto load is applied to the crankshaft forward of the crankshaft timing gear and this is smaller than the forward main crank bearing. I suspect that Yanmar are disinterested in what you hang off the front of the crankshaft..... after the warranty period. They will happily sell you a new crankshaft if yours snaps off at the front pulley. There is possibly an issue with crankshaft harmonics as well even though the 4JH often lack a viscous vibration damper they do have an unbalanced front pulley to smooth things out a bit.
The HP graph probably takes into account the extracted HP at the flywheel end as well as the pto end so if you hit the engine with a 8Hp load at 1500rpm while turning a propeller, the load might cause sluggish spin up and possibly black smoke.
I shared an engine room with a 20 Kva Kohler genset running a 20Hp hydraulic pump that lifted the ballast keel ...... using the D config on the Yanmar 4TNE ( nearly same as 4JH) but the main breaker for that genset had to be off for the engine to hold the hydraulics when lifting or lowering the keel.
There is no doubt that useful power can be extracted from the front of the crankshaft but by what method and how much are the debatable issues.

[GoneDiving]

Originally Posted by skipperpete

I suspect that Yanmar are disinterested in what you hang off the front of the crankshaft..... after the warranty period.

There is no doubt that useful power can be extracted from the front of the crankshaft but by what method and how much are the debatable issues.

So are we talking about Waranttee ass covering or real world limitations?

I realise no OEM is going to condone it but what are some of the practical examples out there that have actually stood up in the field?

The cement trucks that I nominated would represent 25 to 33% of the drive motors hp being extracted. I'm guessing that light trucks with cooling water pumps, radiator fans, air con compressors, altenators, compressors and power steering hanging off the crank would also be a substantial load.

Cheers

[skipperpete]

The warranty is definitely an issue if something goes toes up with a new engine and companies like Volvo go to some lengths to not admit liability and deny or seriously limit warranty claims.
I removed a big ol Isuzu from a cruising yacht and installed a 125hp Yanmar 4JH series. The problem came at the end of the repower. The owner insisted on having all of his “old stuff” re mounted on the much smaller Yanmar and got the 5 row alloy pulley for the crank and I made up a frame that spanned the 4 mounts and supported a cat pump, a refrig compressor and a high amp alternator. The compressor and Cat pump were on a plate in front of the alloy pulley and the alternator was in the standard second alternator position as per Yanmar. Got it all finished and did the sea trial successfully but with no belts on the refrig pump and Cat pump and I flatly refused to put the belts on until the warranty period ended. He was less than pleased about this despite previous discussions and eventually got another guy to hook up the belts.
The message is that since then , that mess of belts and high power demand on the front of the crankshaft has worked very well so it is possible to overload the pto and get away without breaking the engine.

[CassidyNZ]

^^^ As it happens I have two 120A alts off the front of the engine running “backwards” and are not far from the 30 degrees off horizontal. Given the inefficiencies of hot alternators (having them run backwards means the cooling fans are less efficient) I will under full electrical load get about 160A from them which at 25A/hp If the linear stuff discussed before is considered, at 2000RPM I’m drawing about 6.4hp which is midway between Yanmar’s 4 and 8 allowable hp load.

Since I don’t really buy the linear increase in hp, I’m not going lose any sleep over this.

[valhalla360]

If we are talking about a new build or a repower...I would look at diesel/electric in one hull.

Most cats are happy to motor on one engine with almost no rudder needed to keep them running straight. So if the standard cat would have a pair of 20hp diesels go with:
- Hull 1: 30hp direct drive diesel.
- Hull 2: 10kw (13hp) generator feeding a 10kw electric motor with 5kwh (usable) battery bank.

For close quarters maneuvering, the battery bank can drive the hull 2.
For long distance cruising under power, the 30hp in hull 1 will do well and be nicely loaded. Set up properly, it should be able to top up the 5kwh battery bank.
For a short run, particularly if you don't need speed, the 5kwh battery bank in hull 2 can drive the electric motor.
In emergency conditions, both diesels running flat out giving you a total roughly equal to the standard dual 20hp diesels.
At anchor, the 5kwh battery bank could get you through a night of air/con if it's not too hot (cycles off a lot)...otherwise, the 10kw generator is well suited to handling the load and topping up the battery bank.

I would expect the total cost should be similar to a pair of 20hp diesels plus an independent diesel generator for house loads and you lose no capability.

[Dockhead]

Originally Posted by CassidyNZ

So it is presumed that the “allowable hp take-off” at the front on the engine is limited because of the smaller size of the crank journal vs the flywheel end?
Then it is said that the “allowable hp” is a linear relationship to RPM.

So presumably the front crank journal grows in size as RPM goes up allowing it to handle more horsepower? Of course it doesn’t so why the hp change? I still don’t get it.
. . ..

Torque!


And it may not be only the front main bearing -- it can also have to do with the crankshaft itself.



It should not be hard to design an engine which would allow as much power to be taken off the front as off the back, but that's not what we have.

[RaymondR]

Most engine crankshafts have a fairly large diameter flange to which the flywheel is bolted whereas the front end has a keyed and thread retained, slip on pulley with the only torque transmitting component is the key. If both ends had flanges there is no reason that both ends transmit similar amounts of torque. Be mindful that power is torque multiplied by revolutions.

Some large industrial engines, such as those driving the DC traction generators on diesel electric locos, have driving flanges on both ends.

[skipperpete]

Some of the larger engine builders allow more power to be extracted from the PTO but the most striking example is the venerable Detroit Diesel. The V16-71 is actually two V8-71 engines bolted together, even the crankshafts so the rear half takes 100% of the front engine power on what is actually the PTO end of the crank.

[Dockhead]

Originally Posted by RaymondR

Most engine crankshafts have a fairly large diameter flange to which the flywheel is bolted whereas the front end has a keyed and thread retained, slip on pulley with the only torque transmitting component is the key. If both ends had flanges there is no reason that both ends transmit similar amounts of torque. Be mindful that power is torque multiplied by revolutions.

Some large industrial engines, such as those driving the DC traction generators on diesel electric locos, have driving flanges on both ends.

The problem is not the method of attachment to the crankshaft -- the problem is, in the first place, the bearing. If you've ever torn down a car engine then you will know that, as someone mentioned above, the rear main bearing is a jumbo one and the front one is more delicate.



But that is not the only possible problem with taking lots of power off the front of the engine -- the crankshaft itself may not be designed to handle it, and there may be torsional vibration.



As I said, it shouldn't be difficult to design a motor which can have power taken off either end, but that is not the type of motor which we have.


I think it's important to follow the manufacturer's instructions.

[Fendell]

Originally Posted by valhalla360

If we are talking about a new build or a repower...I would look at diesel/electric in one hull.

Most cats are happy to motor on one engine with almost no rudder needed to keep them running straight. So if the standard cat would have a pair of 20hp diesels go with:
- Hull 1: 30hp direct drive diesel.
- Hull 2: 10kw (13hp) generator feeding a 10kw electric motor with 5kwh (usable) battery bank.

For close quarters maneuvering, the battery bank can drive the hull 2.
For long distance cruising under power, the 30hp in hull 1 will do well and be nicely loaded. Set up properly, it should be able to top up the 5kwh battery bank.
For a short run, particularly if you don't need speed, the 5kwh battery bank in hull 2 can drive the electric motor.
In emergency conditions, both diesels running flat out giving you a total roughly equal to the standard dual 20hp diesels.
At anchor, the 5kwh battery bank could get you through a night of air/con if it's not too hot (cycles off a lot)...otherwise, the 10kw generator is well suited to handling the load and topping up the battery bank.

I would expect the total cost should be similar to a pair of 20hp diesels plus an independent diesel generator for house loads and you lose no capability.

Wow! I too have often pondered this exact set up. would love to continue the conversation in a different thread as I think this is a great alternative to re powering with like/like engines, as long as you can overcome the difference in control. Thanks Val

Originally Posted by Dockhead

The problem is not the method of attachment to the crankshaft -- the problem is, in the first place, the bearing. If you've ever torn down a car engine then you will know that, as someone mentioned above, the rear main bearing is a jumbo one and the front one is more delicate.



But that is not the only possible problem with taking lots of power off the front of the engine -- the crankshaft itself may not be designed to handle it, and there may be torsional vibration.



As I said, it shouldn't be difficult to design a motor which can have power taken off either end, but that is not the type of motor which we have.


I think it's important to follow the manufacturer's instructions.

I totally agree with you there, follow the OEM and you cant go wrong.

Thanks all for posting the tech specs from various engines, been really helpful. cheers