Diesel-electric without batteries?

Diesel electric on a rail locomotive is to be able to apply greater torque than the straight diesel could, to get a very heavy load moving... - whereas, - a direct diesel would stall at similar initial acceleration loads... - - and also, - the load can be distributed to many pairs of wheels via the electric motors with greater automatic control and load distribution to improve the ability to apply that torque... - An electric train will out perform a diesel electric using the same kw/tonne (power to weight ratio) because 100% of the torque is available at near zero rpm (watch carefully to avoid wheelspin. - (mechanical engineering 001 - - not even 101 yet).

Diesel to electric (.8 power factor), electricity to motor drive at .8 factor again - lost 40% usable power in the double conversion - - WTF

The high loads on commercial ships to enable slow speed work and still achieve efficient cruise at 15 to 25 knots could justify the heavy cost burden (gas turbine/electric may be preferred in passenger ships because of quietness and less vibration? The cost of diesel electric systems would be difficult to justify for recreational boats... Nice try, but, - that power form has been around long enough to assure most that there are still many unresolved issues...

 

Don't put your money on solar power. Present efficiency is approx. 15% and there will surely be some improvements in the near future, but for the amount of power you have in mind, even 100% efficiency isn't enough. The sun radiates approx. 100 Watts on 1 sq.ft., so do the math.

A good permanent magnet motor can deliver over 90% of the input power to the shaft, the controller is also 90% efficient, so together they waste only 20%. The generator wastes just 10%, so roughly 2/3 of the generated electrical power will wind up at the prop.

And about generators: We call them alternators because they make AC! Add a rectifier and that becomes DC.
There have been DC generators in the past, but they were more expensive to build and maintain.

 

CDK got your efficiency losses to the prop, now don't forget about your losses in the prop.

Most range from 50 -75% efficient, some up to 80 - 90% but they are rare and vary job specific, i.e. speed, weight, RPM, etc dependant.

 

One benefit of a straight electric drive over a hybrid with a battery is the straight electric drive sytem can be AC-AC, AC-variable voltage DC, etc. without the need for a fixed voltage part of the system for a battery.

Hybrid cars are more advantageous in city driving than highway driving. Whether a hybrid vehicle is worse or better than a "similar" vehicle with a manual transmission on the highway depends on a number of factors including hybrid system configuration, hybrid control algorithm, sizes of IC engines in hybrid vs non-hybrid, and size of hybrid battery systems.

If efficiency means the ratio of power out of the drive sytem to power in, then I doubt many electric drive systems can equal or exceed a reasonable direct drive system. The only significant losses in a direct drive system are generally the bearing losses which are generally a few percent at most. An electric drive system has the losses in the generator, motor and controller.

My understanding is there are generator and motor systems available with combined efficiency of 80% or better, such as those used in some hybrid vehicles. Not inexpensive though.

Prop losses are the same irregardless of what is turning the shaft unless the prop changes due to different power/torque vs speed characteristics of the motor or engine.

 

David,

I think you may have missed my point.

Red Dwarf,

In your calculations, don't overlook prop losses.

 

I don't see the point of discussing the prop losses since the prop is a common factor regardless of power source. Are you saying the prop for an electric drive will be different than the prop for a direct diesel drive?

I am doing some reading and trying to get the losses worked out. The way to keep it apples to apples comparison is to talk in terms of energy. In this case I am using a gallon of diesel (20Hp). The direct drive diesel will put 95% of that 20 Hp to the prop,(could be 10% less depending on shaft angle). If the electric has losses of .9x.9x.9 then it is putting 73% of that 20Hp to the prop. Not good.

I eliminated hydraulic mostly due to noise. I have worked with a 300 Hp hydraulic system and the pump is a screamer. For now, let's say we eliminate electric because of poor efficiency.

That leaves me with a gearbox and shaft setup. The diesel engine and transmission will be mounted above the hull with a right angle drive to direct power down and a second right angle drive to direct power aft to the prop. Each of those right angle drives drive is 95% efficient so the total loss is .95x.95x.95 or 85% of 20Hp to the prop. Not bad.

I have not found a suitable right angle drive but I am searching.

 

What about the thrust :?: - where is that going to be borne :?: and there will have to be a thrust bearing to absorb the load before it reaches the 90 degree angle gears :!: and HOW WILL YOU SELECT REVERSE :?: as the load will have to be removed (thrust wise) to engage reverse, or then forward :!:

 

Why the concern about needing a thrust bearing on the shaft? I've looked at commercially available systems which put a thrust bearing inside the boat on the prop shaft, and then a short shaft with U-joints between the thrust bearing and reverse gear. Those systems are simple and straightforward, using "off the shalf" bearings, joints and seals.

 

If that were true,with the hours and mileage put on every year-every semi tractor DE.

I looked into the Siemens system a few years ago...the same one that Nordhavn spent a year trying to get working,couldn't,and tore it out and sued (and won) Siemens.
They wanted $100k plus for the system on my boat...even if I got 5% better mpg (which it never would) I'd need to circumnavigate the world 3 times to pay it off.
Honestly-what's up with the Germans making things so complex? Look at their cars.


IIRC the gens were 90% the controllers (needing water cooling) were 95% and the motors were 90% which is 75%.
Marine transmissions are well over 90% and I've read 95%.
Plus you have a suitcase sized electronic controller..try finding the one microscopic resistor on one of the chips that got cooked by a nearby lightning strike.

However if you can put in used stuff,keep it cheap and only use the boat on odd weekends for the summer and don't expect nirvana-why not?who cares about and extra bit a year for diesel.

BTW I also read the use of DE in oil rig supply and tugs is they can/or will use electric thrusters or Azis..hit the GPS and the boat will hold a location or path on it's own, regardless of current.

 

This doesn't make sense. You put the thrust bearing on the stub prop shaft, after the last set of bevel gears. You need some lower level of thrust for the bevel gears themselves but if you buy the right angle boxes off the shelf, it's all built in. I'd probably couple with Fenner or Lovejoy flex couplings or similar.

I wouldn't regard a system with a double right angle drive system as particularly efficient, but it's certainly easy to do. Another benefit being that either of the RA drive pairs doesn't have to be 1:1 so you can further drop your g/box ratio if you so desire.

PDW

 

Hi.
I'm putting a diesel/electric propulson in my boat/boats.
Due to lack of funds, the physical plant hasn't been purchased, but I am now working again, (first job in 2 years) so hopefully soon have the components.

The drive you fnd difficult to fnd, beleve is cheap and avalable. The lower unt of old outboad motors. I ntend using two for twin screw. Also 360 degree azmuthing.

The motors, 3 phase 220, permanent magnet and brushless, just as Tesla designed them over 100 years ago. Plentifull and cheap and efficient.

Gen set, diesel and 220 single phase alternator.
3 phase can be run off of single phase ac.

No line loss as in dc current.

Varable speed? cvt scooter transmission.

The savings in initial cost and fuel consumption occur because a smaller diesel serves as a generator, operating at most efficient power and constant speed.

Two drive motos and props can run from one gen set.

and all of the technology is off the shelf and available used or new over most of the world.

 

At least 2 methods to covert single phase to 3 phase.

http://www.youtube.com/watch?v=e6eKDsDpup8

and

http://www.youtube.com/watch?feature=player_embedded&v=SOxNjsuUrZA#!

searching shows more sites and info. two links above are couple of best i found

 

the outboad lower unit electric drive

http://www.glen-l.com/designs/special/electricdrive.html

except propose Ac instead of a Dc motor.

 

Belts are not no loss , the Hysteresis of bending and unbending them costs power.

Stick the motor straight up if you can .

 

This is the real reason. trying to change speed or reverse on a large low speed diesel engine take time and not very efficient. Electric motor was added for ease and speed of control.
This is valuable for a 20 liters and up, 600 or 900 rpm EMD or ABC engine.
Modern locomotive use a sophisticate system of DC and AC electrical transfer to the motors directly linked to the wheels.
If your boat weight around 200 tons, than can be considered. But even then a high speed diesel and trany will be recommended. For a small yacht, a classic let say Elco, will be nice. They provide a system with genny.
But all that is not that efficient and outrageously expensive, compeer to a simple engine, trany and shaft. Nothing is better in the cost/efficiency.