Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don, Maciek.
I am just back from 3- days travelling with limited access to the net, sorry for not answering and thanks to Maciek for the correct answers. A few reflections on the external ballast /fueltanks. We did not use the mbts 2 and 4 as well as the regulating/fuel tanks as bunkertanks a lot . The reason was that we used the VIICs more as a coastal submarine ( a long Norwegian coast up to the Barents sea, having easy access to fuelingstations contrary to the German long warpatrols which even force them to use milkcows. We used the external fuel/ballast tanks occasionally for training only.
Watercompensating. Having watercompensated fuel tanks is giving an extra benefit by eliminating the free surface effect as well.
Tore

[VIC20]

Just in case that someone wants to know more details about the effect of hull fouling - this old 1952 document shows a lot: https://darchive.mblwhoilibrary.org/bitstream/handle/1912/191/chapter%202.pdf?sequence=9

[VIC20]

Next version of my engine simulation which prints acceleration over time now - I think it is almost OK (except that it is a little bit too fast at max) - seems acceleration fits to what Tore said.


http://www.hessburg.com/downloads/Engine2/Engine2.html

[tore]

Mark.
Amazing! One question, as you are using the parameters primarily in the SI system why do you have a bmep in psi? I cant get the bmep figures to match the bmep.
Tore

[VIC20]

I'm sometimes using formulas with non SI inputs. But I've used psi when I wanted to compare the results (while using the Type IX engine settings) with the one on page 10 of this document:http://www.uboatarchive.net/DesignStudiesTypeIXC.htm

[tore]

Mark.
I am modifying my post
Come to think of it. The figures recorded ( bmep of 6,8 psi ) could match to average  bmep in the SI system (bar sq.cm) of the GW engines without Roots blower connected, I don`t have the figure at very low revs, however the MAN engine at 1/10 load  and 218 rpm has a bmep of 24 psi.
Tore.

[VIC20]

Sorry for late reply, I was offline because the router died.
I've used the MEP to compare it to the data of the Type IX. The printed MEP is based on the calculated torque and the cylinder data. It was extremely close to the IX engine when I've tested it with the IX data. I don't know if it currently prints out the correct values maybe I mixed up units during recent changes but I think it should be correct. Will take a closer look at it when I'm not tired ;-)

[Don Prince]

Hello Mr. Tore,


Again some basic questions on soundings, venting, and test piping ....


Q1.  What is soundings?  Do they take a stethoscope and listen for a tank to hisses or hear drips in the compartments?


Q2.  Fuel oil tanks generally are full of fuel to start, then water gets pumped into the bottom which forces fuel oil out the top.  On plate 8 and 8a, there are vent lines at the top of each tank that feeds into a measuring bucket.  What are they measuring?


Q3.  On Plate 8 and 8a, there are lines at the bottom of the tanks that feeds up to a collection funnel and it looks like it's dumped into the ocean.  Why are they doing this?


Q4.  I can't figure out how the 3 way flooding cock with lateral inlets works on Plate 8a.  photo ttached...


Regards,
Don_

[tore]

Mark.
 I have slept on your bmep in psi and guess related to the 48,5...SHP the low figure is OK. I have never reflected over or noticed it takes only 48,5....SHP for each engine, thus  a total of only 97,...SHP to push a VIIC through the water at 6,2 knots, slightly more than 1/3 of the max speed.
The US figure on a  9 cyl transferred to a 6 cyl and with Roots blower at max load, I assume would be approximately:
Max cont. 1346 SHP,460 rpm,115 psi bmep, 3/4 load 1086 SHP, 126 rpm, 95 psi bmep, 1/2 load  720 SHP 383 rpm, 72 bmep  psi, 1/4 load 361 SHP, 295 rpm, 45 psi bmep, 1/10 load  (being the lowest output they registered ) 144,5 SHP, 218 rpm, 24 psi bmp.
I do not know where they got the figures. You can not transfer the load figures based on a IXC directly to a VIIC as the hull size and lines are different, but may be it could give an indication.
Tore

[VIC20]

No, you are right something is wrong. 

[tore]

Don.
 Q1 Sounding is measuring quantities of liquid in a containers or tank. It is done in several ways like oilchecking on you car using a dipstic. Some tanks the VIIC engineroom are equipped with a kind of dipstick. Q2. The fuel/ ballasttanks have a different system based on smaller pipes,cocks, funnels and a graded container inside the pressurehull , see discussion page 46-47 on this thread .Q3  When you are fuelling, the fuel force the seawater out of the tanks and you monitor the waterlevel by the pipe going almost to the bottom of the tank by the valves ( cocks) on the top of the tanks outside the pressurehull. As soon as fuel is flowing out of the valve (cock) you stop fuelling and prevent fuel spills and as the checkpipe stop some 10 cm above the end of the compensating pipe some compensatingwater residue is left in the fuel/ballasttanks.. I have discussed the whole system on page 47 and 46 on this thread.
Tore

[SnakeDoc]

Hi Don,

some time ago, Tore described this system here:
http://models.rokket.biz/index.php?topic=921.msg12479#msg12479

Q1.  What is soundings?  Do they take a stethoscope and listen for a tank to hisses or hear drips in the compartments?

The term "Sounding" is quite misleading in this context. The German, original term is "Peil-" - that means gauging, indicating, or probing.
Simply - Peilleitung - installation for measuring the amount of fuel in the fuel oil tanks (internal as well as external).

Q2.  Fuel oil tanks generally are full of fuel to start, then water gets pumped into the bottom which forces fuel oil out the top.  On plate 8 and 8a, there are vent lines at the top of each tank that feeds into a measuring bucket.  What are they measuring?

See Tore's explanation.

Q3.  On Plate 8 and 8a, there are lines at the bottom of the tanks that feeds up to a collection funnel and it looks like it's dumped into the ocean.  Why are they doing this?

These lines are used while filling the tanks with fuel oil. Initially, the tanks are filled with water. Then, trough the fuel oil transfer lines the oil is pumped. These fuel oil transfer lines have their outlets at the top of the tanks, so the fuel is gathered in the upper part of tanks, while the water is forced out through the lines, you are asking for. The crew member is watching the funnel at the upper deck - if from the lines outlet start leaking fuel instead the water, it means, that the tank is filled with fuel and the pump is turned off.

Q4.  I can't figure out how the 3 way flooding cock with lateral inlets works on Plate 8a.  photo ttached...

Based on Tore's description, some time ago I have prepared some drawings, which can illustrate the process of fuel oil amount measuring.

fot 1.jpg - forward bulkhead of the U-570 control room with visible fuel oil probing lines.
fot 2.jpg - forward bulkhead of the U-995 control room with visible fuel oil probing lines and collecting bucket.
fot 3.jpg - control valve of the probing and venting installation in the control room of U-995
rys 7.png - probing of the internal fuel tank - equalising the pressure
rys 8.png - probing of the internal fuel tank - measuring the amount of fuel


--
Regards
Maciek

[VIC20]

The term "Sounding" is quite misleading in this context. The German, original term is "Peil-" - that means gauging, indicating, or probing.
Simply - Peilleitung - installation for measuring the amount of fuel in the fuel oil tanks (internal as well as external).

Peilen is a pretty unusual word for that esp. "Peilleitung" which I've never heard before - but the german word for the oil-level dip stick is "Peilstab" or more common "Ölmeßstab" hence it makes sense that they might have used it during that time.
From the logic of the word it should be used like you said to read the amount of fuel from a nonlinear scale.
But the word Peilung and peilen is mostly used for bearing and targeting and for understanding something - "I don't peil it" means "I don't understand it" - "I have no Peilung" is "I have no idea"

[SnakeDoc]

Mark,

The term "Sounding" is quite misleading in this context. The German, original term is "Peil-" - that means gauging, indicating, or probing.
Simply - Peilleitung - installation for measuring the amount of fuel in the fuel oil tanks (internal as well as external).

Peilen is a pretty unusual word for that esp. "Peilleitung" which I've never heard before - but the german word for the oil-level dip stick is "Peilstab" or more common "Ölmeßstab" hence it makes sense that they might have used it during that time.
From the logic of the word it should be used like you said to read the amount of fuel from a nonlinear scale.

Term "Peilen" is commonly used in the  Tauchvorschrift.

But the word Peilung and peilen is mostly used for bearing and targeting and for understanding something - "I don't peil it" means "I don't understand it" - "I have no Peilung" is "I have no idea"

You are right. The most common (today) usage is as bearing.

--
Regards
Maciek

[VIC20]

Term "Peilen" is commonly used in the  Tauchvorschrift.

I guess the usage was dropped quickly within the last decades. Actually I can't remember someone saying that. But a quick search shows that some people still use it today. (but much more people use prüfen, messen or kontrollieren). The word Peilleitung is even more rare, just 28 results with google and I think of those only one was a real hit (about a Peilleitung in an oil tank)
I really never heard that word before today. It's funny to learn something about my own language on an english speaking forum.