I wish about engines...
 

Hell yes.
I wish i would be able to put one engine "ahead" while other "back". It would really help to steer the boat in emergencies.
Than there should be an option to manually switch to electric engines for silent aproaching. It would be of course an option to save fuel (using engines only to load batteries).

Theres typically 4 engines but yes Ive been asking for this since SH2 :yep:

Furthermore we should be able to run the electrics on the surface if we want as well.

You can't run the diesel engines underwater if you don't have a snorkel, because the diesel engines need air to run.

but i want to be able run electric on surface. Not diesel submerged.

I completely agree. Typically a 'decks awash' attack was made on electric motors because they are silent. Also maneuvering in port is easier because you have much finer control with the electrics.

And you don't set off brit accoustic mines which I also hope is included.

Not to forget the combined diesel-electric propulsion for saving fuel on long journeys... that would be nice.

German boats up to the electro boot, had two direct drive diesels that had only forward ability. The electric motors acted as generators when the diesels were running but were clutched out when the batteries were full up.
The diesel engines had to be clutched in and out for operations. While in harbor the U-boat operated on only electric motors due to the limitations on backing.

Only Us boats, and the type IXD2 had more than two diesels and only the fleet boats from the very start had diesel electric-propulsion.

The S boats were very much like the German propulsion system of earlier boats.

The downside to a direct drive propulsion system IMO. Diesel propulsion too to a degree. But I remember Enigma had the option for individual propulsion controls, i.e. ahead flank on the stbd and back emergency on port.

god yes, order pivot port and your ship will heel and do its pretty tricks...ordered that a lot when avoiding torpedoes :D

You do not save fuel by running on electric power.

More fuel is required to charge the batteries and run on electric for 10 miles
than is required to run for 10 miles on diesel alone.
This is because some of the energy the diesel engines produce is lost when
they charge the batteries.

The only source of energy on the u-boat is the diesel fuel. You can convert
it to battery power, but that results in an overall energy loss. You can't get
'free' energy.

Electric cars save energy because they charge the batteries when there is
excess engine power and discharge when the engine would otherwise be at
it's least efficient. U-boats can't do this because their combustion engines
always run at speeds that are less efficacy when switched to electric and
there is never any spare engine power.

@Letum
Maybe my formulation was a bit unclear...

There´s a procedure described in many books... run diesel AND electric engines together. This takes some load off the diesels = saves fuel.

The engine technology is quite plain to me. It´s my job every day :D

I know that could be done to add half a knot to the top speed, but how did it save fuel?

I think I know what he's talking about.

One diesel engine would turn the electric motor and the propeller. The electricity from that motor would go to power the other electric, which was connected to the propeller, but the diesel on that side was off.

Exactly! Couldn´t have say that better.
Earlier i was too lazy to find that book... it was 1 o´clock in the morning here :DL

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.