Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Mark.
It is much better, however I cannot figure out the specific fuelconsumption. At these revs and the Roots blower disengaged, I should assume it would be more like max. 200 g/bhp hour rather than 415 g. The acceleration time 0 to 6.8 knots in  9 minutes astonish me based on my feeling, but I guess it is probably OK. so I should n`t worry.
Tore

[Don Prince]

Gentlemen,


I have been looking at Plate 13 and the cooling water flow.  It looks like plate 13 does not agree with Plate 13a and 13b.  Was plate 13 drawn wrong?


See the attached drawing...


Regards,
Don_

[tore]

Don.
Your observation is correct. It is a mistake in this particular drawing and the stb enginepump , the reserve coolingwaterpump and the coolingwater handpump shall all have a connection to the crossover seacoolingwater suctionpipe. Plate 13 has a mistake.
Tore

[NZSnowman]

Hi Tore

I was just checking our cooling piping of U-1308, and I noted I have missed two things:

The Pressure Gage between the Aux CW Pump and the manifold,
And the Compressed air chambers between the CW pump and manifold.

Where would the Pressure Gage be located?
What do the Compressed air chambers look like and size?

Thanks, Simon.

[tore]

Simon.
I guess plate 13 is a bit misleading. I don`t think it is a compressed airchamber in the line it is rather the airvessel on attached pistonpump driven from the engine, see drawing below. The pistonpump has such airvessel as a buffer to ease the pressure pulses from a reciprocating pump, not needed for a centrifugalpump. The manometer could be the one up on the instrument panel front top of the engines, showing the cooling waterpressure to the engine.
Tore

[VIC20]

Mark.It is much better, however I cannot figure out the specific fuelconsumption. At these revs and the Roots blower disengaged, I should assume it would be more like max. 200 g/bhp hour rather than 415 g.

It's both for for both engines but only written on the first one. I've just multiplied it by 2 for the display

The acceleration time 0 to 6.8 knots in  9 minutes astonish me based on my feeling, but I guess it is probably OK. so I should n`t worry.
Tore

If you think it's too slow then I need to change it. But thrust is pretty low at these RPM.
When I get rid of one of my new faked stuff then the acceleration curves for KF, LF, HF, GF & AK look like this, are they better?

[tore]

Mark.
I am afraid you cannot multiply the specific fuelconsumption for two engines, as it is specific per bhp per hour thus has nothing to do with the total bhp as the fuelconsumption.
As to the acceleration, you are right, the thrust is pretty low for a fixed propeller at low revs and as my remark is based on feelings I don`t think you shall change it.
Tore

[VIC20]

I guess you misunderstood me?

The fuel consumption is based on the data of the curve "fuel consumption per hp" - it's calculated for one engine and this result of a single engine is then multiplied by 2 because two (almost identical) engines are running.


It's not like bhp = 100, 100*2 = 200, 200*fuel consumption@200
It's like bhp = 100, fuel consumption=100*fuel consumption@100, fuel consumption*2

[Don Prince]

Hello Mr. Tore and All,


I have a question about Regelbunker RFO tank 1 in the saddle tank...  Since this tank does not have a pipe from the header/buffer tank to provide a water replacement for fuel taken from the tank.  Is this tank only a storage/transfer tank and not capable of being a direct fuel source for the diesel engines?


Regards,
Don_

[tore]

Mark.
Sorry I misunderstood.
Tore

[tore]

Don.
Yes and no. It is a non watercompensated tank, but can be used as a direct source as the other tanks. However normally it is no bunkertank in direct contact with the engines as the fuel supply pipes end in the "day tank" a double settlingtank above the engines. You top up the daytank from the fuel tanks, let the fuel settle for a while so possible impurities and water can be drain while running the engines from the other tank where the fuel has already settled.
Tore

[Don Prince]

Hello Mr. Tore and All,


Now on to the Diesel fuel system...  I believe I'm close to understanding some of the functionality.  I will attach a fuel flow from Plate 9.  However, as usual I have a few questions:


Q1.  There seems to be no fuel level control in the Gravity Tank that's mounted above the walk-way between the engines.  How do they know when the tank is full, and which valve would they normally use to shut off the flow of fuel?  The same with the Collection tank except fpr the goose neck over flow spout.


Q2.  The 4 pipes coming from the gravity tank go to a collector and then to the Collection tank (I believe this tank us below the metal walking deck).  Should all 4 pipes go to the collection tank.  I would think that 2 of the pipes would be for settlement and water draining?


Q3.  I'm not exactly sure about valve "e" the change over cock with central passage.  I know it allows fuel to enter the what looks to be a separated gravity tank.  When it's feeding the other side with the drain and tank for the Junkers compressor, I'm not sure about the 2 lines going to the gravity tank.


Q4  The small bypass line on the fuel pump...  this line has a safety valve to open if the pressure gets too high.  How will this ever work because there is a huge bypass line on the outside of the pump?


Q5.  It was stated in one of the manuals that if one of the fuel pumps failed, then the Aux. Pump could be used in it's place.  If this happened, was there the possibility to fix or replace the fuel pump?  With the Aux pump providing fuel for one of the engines, would not the gravity tank stop getting fuel?


I guess that's my quota of questions for today...


Regards,
Don_

[tore]

Don.
Q 1 There are two sight glasses each for port and stb up front of the settlingtanks. Q 3 Cock "e" shut the fuelsupply to the settlingtanks and is shown in shut position on plate 9.
Q 2 Fuelcollecting tank has nothing to do with the fuelsupply to the engines it is merely a collectingtank for the fuel drain and overflow pipes from the settlingtanks, filters,pumps etc . Fuel supply from the bunkertanks to the distribution box is drawn OK, from this box the supplyline goes to the distribution selector cock "e" which has 4 positions: A. shut to the settlingtanks and engines as shown on plate 9. B ,the unusual, daytank shut and fuel goes straight to the fuel supplypump on the engines,C topping up port settling tank and supply to the engine supplypumps from stb. settling tank and D, topping up stb settlingtank and supply to the engine supplypumps from port settling tank. See drawing below.  Q4 The plate 9 shows more a MAN arrangement than  a GW engine. On the GW engine the engine driven fuelsupply pump is up front of the engine. The "huge" pump bypass as you express it is normally shut and is only used when something is wrong with the pump. The relief valve has a normal dimension don`t get confused, look at the photos on the front of the engines.
Q.5 I am not sure if I understand your question right. If you mean the HP fuelpumps on the engines, the engine had to stop and a spare pump fitted, routine.
Tore

[SnakeDoc]

Hi Gentlemen,

Q.5 I am not sure if I understand your question right. If you mean the HP fuelpumps on the engines, the engine had to stop and a spare pump fitted, routine.

I believe, that Don is asking about auxiliary lubricating oil pump - but it is only used while taking fuel oil on board.

--
Regards
Maciek

[tore]

Don.
If you assume the aux. luboil pump should be used as Maciek says, I am afraid you got the fuel transfer system screwed up. All the fueltanks are as you know seawatercompensated except the F.O. regulating tanks. This means the F.O. bunkertanks are always under the head of the watercompensating tank high up in the towercasing ( not the wintergarden as you have mentioned) assuring the settlingtanks are having a supply pressure at the tank of 2- 3 m.W.C. This means that no fuelpump to transfer the fuel is necessary. The waterpressure derive from the attached cooling waterpump on the engines and the outlet to the headertank is at the exhaustmufflers in the casing. The headertank is always topped up in this way when the engines are running and normally you top up the engineroom settlingtanks when the engines are running. If you for some reason would like to transfer fuel from the FO tanks when the main engines are not running, you use the electric driven reserve coolingwater pump or even the handpump to keep the watercompensating headertank topped up giving sufficient head to the fueltransfer. As to the reserve fueloil regulating tank, you normally use air under low pressure for fueltransfer.
Tore