[BUG / ERROR] The Silent Service - The Enemy Below

[StellarRat]

My reading seems to show a very uneven upgrade process on these WW II leftovers. Even within the same class not all of the subs received the same upgrades. To really make a correct set of numbers requires research into the individual subs by name. If you read articles about the actual Segundo it never mentions some of things that various people here have assumed were done to it postwar. Like wood says it's confusing.

[thewood1]

Thats why they were all classified as Migraine 1/2/3/4, GUPPY I/Ia/II/II, and a basic fleet snorkel program. Plus there were probably a dozen individual experimental upgrades. Post-war mostly fell into one of these categories. Late war is where is gets confusing because engines, sonar, and a few other things were swapped out based on availability. There was very little pressure to upgrade USN subs because they were no where near as threatened by IJN ASW efforts. Most of the upgrades were for range during the war.

[Quark73]

Eventually this can be fixed by adding a speed band. Stop, creep and cruise fill battery, full is battery neutral and flank speed drains battery.

[thewood1]

I finished reading Helion's "GO FIND HIM AND BRING ME BACK HIS HAT" book on ASW ops in The Falklands. Its one of the few well-documented and balanced reviews of "modern" ASW ops.

The Argentinians had a Guppy IIA from the US and a German Type 209 acquired in 1974. The GUPPY mod sub had a lot of issues. But the 209 was much more successful in its ability to move around without detection, despite having a large number of things working against it. The relevancy to this topic is one night when moving in close to shore to avoid sonar detection, the captain kept the 209 on the surface to avoid shoals. When they reached the cove they wanted to, they slowed and stopped to fully charge the batteries so they could submerge. They could not charge them fully and still maintain the speed to get to the cove before daylight.

Again, not definitive, but the along the lines of what we are discussing.

[thewood1]

From the OP, who has gone silent...

"Surface the sub. Set speed above 8 kts. Battery will drain, but it shouldn't"

Also noticed that the battery does not drain at 8 knots on the surface. It starts to drain very slowly 9-12 and then drains a little faster at fast speed.

[artao5]

Draining battery at 9 kts is ridiculous. When running at max speed sure, I can accept that.
Subs had/have multiple diesel engines and generally use them all when surfaced to drive the boat. When the batteries need charging some diesel engines are diverted to do that. It's quite uncommon that the diesels need to be supplemented by the batteries. They most definitely do not need to be engaged at anything below flank however.

[thewood1]

OK. So when did that change in CMO?

So is anyone going to bring any sources? Or this still based on a movie?

[boogabooga]

So is anyone going to bring any sources? Or this still based on a movie?

I'll offer this:

https://maritime.org/doc/fleetsub/chap6.php#6A

Also as a sanity check, the 4x GM 16-278A diesel engine arrangement that was used on many of the Balao class was also used on the Evarts class destroyer escorts, which also had similar displacement. Those were also capable of 19-22 knots with no battery to speak of, so I think it's safe to assume that the Balao's should have been capable of at least near top speeds without having to discharge the battery in normal operation.

Eventually this can be fixed by adding a speed band. Stop, creep and cruise fill battery, full is battery neutral and flank speed drains battery.

I think we might be able to clear some of this up with a request on the database GitHub to resolve the various fleet boat performance bands (and sensor fits). We don't need to track each individual boat; there are already database entries for the wartime boats and each of the fleet snorkel/GUPPUY configs. Do we have all the data together? Who wants to do the request?

I think that the only "hard-coded" problem is the CMO assumption that all diesel subs have a snorkel, whereas most of the actual wartime subs did not.

[thewood1]

"I think that the only "hard-coded" problem is the CMO assumption that all diesel subs have a snorkel, whereas most of the actual wartime subs did not."

I think this is the biggest issue out of the whole thread. As mentioned, the WW2 subs, ships, and airplanes have never had the scrutiny that later units had. They are basically MVP for their era.

Looking at that link validates some of the discussion on the main diesels charging battery sources already post. Note this:

"One auxiliary generator: direct current, rated at 300 kw at 1,200 rpm, and driven by a directly connected diesel engine. It is used to supply current to the auxiliary power system and for battery charging"

As I mentioned above, these were installed in mods and later subs specifically because a sub on the surface at speed and with air circulation running could not charge batteries. And the power cubicles were designed to allow full diesel and battery power to both shafts to generate more speed.

[Quark73]

Hi @all I am not a submarine specialist but it seems this issue is discussed quite passionate.

Here is an excerpt, concerning Diesel/Electric modes of operation, of an evaluation Americans did on German class VII C submarine. Which is clearly a WWII model. Event it's not Balao class it's a good example and many early post war designs are quite similar.

Inter-operation of the engines and motors.
a) General.
The diesel engines provide a maximum surface speed of about 18 knots and both E-motors provide a submerged speed of 8 knots. The different working modes are listed below:

Diesel engine only drive,

E motors only drive,

Support and buffer mode,

Diesel-electric drive,

Charging mode.

Exhaust gas from both diesel engines can be diverted and used for blowing out the main ballast tanks and main ballast and reserve fuel oil tanks.

b) Diesel engine only drive.
In diesel engine only drive; both diesel engines drive the propellers via the diesel engine couplings, E motors, main couplings, thrust shafts and the propeller shafts.

In this arrangement the E motors are just a part of the drive train and the armatures are unpowered. The fan blowers of the E motors rotate slowly powered by voltage generated due to the remanent magnetism of the unpowered rotating armature.

c) E motors only.
With E motor drive only, the diesel engine coupling is un-clutched. The E motors are powered by the battery and work as motors driving the propellers via the main couplings, thrust shafts and the propeller shafts.

d) Support and buffer mode.
In support mode, the output power of the diesel engines is increased by switching on the E motors additionally. Each diesel engine via the diesel engine coupling and in addition each E motor acting as a motor drives the propeller. The buffer mode is used in rough seas. The diesel engines drive the ship's propellers as in "Diesel engine only drive". The E motor voltage is adjusted such that with normal conditions the loading and discharge current are equal to zero. If the screw runs above the surface, thus causing unintentional reduction of load on the diesel engine, the E motor works as a generator preventing an inadmissible increase in diesel RPM.

e) Diesel-electric drive.
Diesel-electric drive allows driving both propellers even if one diesel engine has failed. The operational diesel engine works directly driving the propeller on its side. The E motor whose armature would normally run idle, works as a generator delivering power to the other ship side. The E motor on the other side drives the propeller; the diesel engine clutch is disengaged. The current from the primary E motor can either be switched in such a way that it only drives the secondary E motor or an additional light charge of the batteries takes place.


f) Charging operation.
Charging operations can be differentiated as follows:

Charging with a disengaged propeller shaft,

Charging while running on the surface with diesel engines.

When charging with a disengaged propeller shaft, the diesel engine drives the E motor via the diesel engine clutch. The E motor runs as a generator and charges the storage batteries.
When charging while on the surface with the diesel engines; the diesel engine power drives the propeller. At a constant number of revolutions from the diesel engine, the E motor charges the batteries. In this case, the diesel engine must provide power for the propeller and for charging.

As I understand there are three modes where diesels and electric engines worked together as propulsion:

- Diesel-Electric Mode when one diesel engine has problems
- Buffer Mode to prevent diesel engines screwed up in heavy weather conditions
- support mode to get an extra kick

Next picture shows the speed table of each drive:

VIIC_speeds.png (48.81 KiB) Viewed 271 times

KF- is Kleine Fahrt - Very Slow Speed / Creep
LF - is Langsame Fahrt - Slow Speed
HF - is Halbe Fahrt - Half Speed - Cruise
GF - Ganze Fahrt - Full Speed - Full
AK - Äußerste Kraft - Emergency Speed - Flank

3 x AK means emergency speed on all diesel engines plus electric and give an extra of about 0.5 knots, which is close to hull speed. I guess this is rarely used, only if you really get away of something.

Next is a DB exceprt for the Balao diesels from CMO DB:

SpeedAltitudeElectricEngine.png (13.79 KiB) Viewed 271 times

It simply assumes that electric engines are always supporting the diesels. IMHO this is an oversimplification. Since the CMO code is not known to me, I guess it needs both DB and code adjustment.
I still suggest to use four speed bands:
- stop - creep: fast reload
- creep - cruise: slow reload
- cruise - full: no reload
- flank: battery drain