Yes, but how does that save fuel?

The running diesel has to burn more fuel to run the alternator and charge
the battery. The electric motor can not possibly be more energy efficient
than the motor used to charge it.

If the diesels run most efficiently at 7.5 knots and hooking up the alternator
reduces speed by 2 knots, but running the other electric increases speed
by 1 knot you have lost 1knot of speed for the same volume of fuel burnt.

Why does the diesel lost 2 knots charging the battery, but the e-motor
only give out 1 knot? Because the alternator, rectifier and e-motor all
introduce additional inefficiencies in the energy transfer from fuel to
propeller.

The most efficacy way to use the diesel motor is direct to the prop shaft.
That way you only have the energy loss caused by the inefficiencies in the
diesel motor. If you instead transfer some, or all, of the diesel engine's
out-put through an alternator, rectifier, batteries and motor you introduce
many new inefficiencies that will result in less power per gallon of fuel.

Energy Transfer Loss. Isn't that the proper name for it?

Submarine Propulsion System 101:yep:

There was only one German boat with more than two propulsion engines. The Type IXd being the only one with more than two, and that was a failure. This boat had the engines connected directly to the propellers through a complex shaft arrangement, this along with the general design of the engines made this system very problematic. Though these were the fastest boats for their time. They were relegated to cargo duties after having the complex propulsion system removed and replaced by the standard German system.

The way the German boats worked was they had Diesels that were directly connected to the propeller shaft, which was connected by a clutch. On the shaft was connected the Alternator/motor. When on the surface and charging the batteries one propeller was disconnected and the diesel turned at the highest stable rpm and turned the alternator. This is the side that charged ONLY the boat's batteries.

The other engine was connected to both the propeller as well as turning an alternator, which provided power for the boat's systems. The electrical load to run the systems was a fraction of that needed to charge the batteries.

When the batteries were charged, the charging diesel would be clutched to the propeller, and both power plants would be used to both keep the batteries charged, and provide the power for the boat's systems, as well as provide propulsion.

Now, when running on electrics, the diesels were clutched out from the drive line, and the alternators became propulsion motors. During an alarm, the diesels would be de-clutched pretty much at the same time they were shut down (Sh shows this accurately), after the boat was pushed to flank speed to facility a quick dive. The electrical connections were made to make the alternators act as motors.

All American fleet boats had four engines that were connected to only a generator. THEY WERE NOT CONNECTED TO THE PROPELLER SHAFTS.
The American system was MUCH different. (as was the electro boots) These boats were propelled by electric motors at all times. The diesels powered either the Boat's systems, or charged batteries, OR, provided the power for the drive motors. When the batteries were charged, the Diesels kept the batteries charged and the boat's systems were powered off the batteries (similar to how your car's battery is the source of electrical power for its systems), and provide power for the drive motors.

This propulsion is not unlike the system on a diesel electric locomotive. There is no buffer like a battery between the motor and generator, and so the rpm of the generator directly effects the speed of the motor, hence the reason as the boat slows down the rpm of the diesel slows down. Below a specific RPM the alternator is shunted out, and the motors switch to batteries, or stop.

During a dive there is no time when the motors would stop turning (sh4 inaccurately depicts this) and when charging the batteries both propellers were turning.

The type XXI, and type XXIII operated like this as well.

The S- boat however was much like the German system for boats before the XXI. These also could get assistance from the electric motors when running at flank speed, but this drained the batteries,and no charge was applied to the batteries to keep them charged since the generators were in the drive motor connection. These motors/ alternators acted as either a motor or alternator. They could not act as both at once, not electrically possible. German boats (to my knowledge) did not do this assistance and just went flank through the sheer power of the diesels.

Now, here is something most don't know. The real early boats had constant speed engines (ones that turned at 1 set rpm, usually VERY high). The boat's speed and direction was controlled by changing the pitch of the propeller blades!! But these could be backed up on the diesels and one could be pushing while one pulled, for maneuvering.

More info on Controllable Pitch Propellers...

http://en.wikipedia.org/wiki/Control...itch_propeller

Dident WWII era subs have fixed pitch? Sorry I dont know.

Yes WWII had fixed pitched props.

It was only the early Paraffin powered boats of the German navy that had this feature, and it was very troublesome.

CPPs are a very complex thing. Think about it, you have control rods running down the center of a hollow shaft to linkages in the screw to change the pitch of it. That's a lot of mechanics involved.

As a physisitc, I totally see where Letum is coming from though. You'd think that A->B->C couldn't possibly be as efficient (or more outrageous moreso) than a straight A->C system.

I believe where the magic is happening is that decoupling the propeller(s) and diesel engine(s) lets you run them at their own individual best-efficiency speeds. Bolted together they must compromise between the two and take a hit to their combined efficiency that nullifies the benefit of having less energy transitions in the chain.

You'd think a proper gearing arrangement would be even better than diesel-electric as it would allow them both to spin at efficient speeds with a more direct mechanical connection over a more lossy one.. It's absurd to think you're getting energy for free. If that was the case you could ride a bicycle that powered an electric motor that turned a shaft that turned a generator that powered a motor that turned a shaft... and all of a sudden you're powering all of Eastern Europe.:har:

Sure they did it!

This is how Prien got out of Scapa Flow again!

To which nation boats are you reffering now ?

Lets get the facts straight gentlemen. There was exactly one u-boat build for the imperial german navy that had controlable pitch propellers and this was the SMU 1. This configuration was given up since then because of the low efficiency of this sort of propellers.

For more info check my website:
http://www.dreadnoughtproject.org/he...r%20backup.htm
http://www.dreadnoughtproject.org/heinrich/

And what exactly is your job ? :hmm2:

Deamon

You are correct about only one of the Kaiser's boats having controllable pitch props. However it was not the only German boat to have this. The small boat the Forelle had one, and the Karp, Karas, and Kambala, had these propellers. These were German made boats, but served in Russian navies. In my post I said the really early boats, nothing about the nation under which they served.

Prien's escape from Scapa was done on the surface? I was not aware of this. Nice to have an armored sub eh? My understanding is he escaped submerged due to the number of naval ships in that small harbor. I have really just concentrated on the tech of the boats, and the strategy of the Grand Admiral. Can you recommend any books about Prien's attack?

I know it is a game, but when I try this attack, that is how I do it, the whole approach is done awash, and then submerged, and remain submerged. I have unfortunately not read much about Prien's attack.

(I just looked at your site, Very nice. I like. Are you still trying to make a sim?)

If I remember right, Prien was forced to exit surfaced as there was such a strong current into the harbor, that only the diesel engines had enough power to get out.

Upon some research, I stand corrected about his escape. However, looking at the tech descriptions of the charging system, there does not appear to be a method of engaging the motors for propulsion when operating at flank power. I will continue my research.

Here is the best site I've found on Prien and Scapa Flow. It gives all the details of the attack, including the escape - on the surface.
http://www.u47.org/english/index.asp

These features about the engines being all freely maneuverable is definitely a must-do on the wishlist of everyone... I can tell you we've been wanting this possibility all since SH2 in the 24th, I'm sure there's more people that thinks the same and I hope we can get it. :DL

Cheers :rock: