Diesel Exhaust Outlets

[NZSnowman]

Hi Dougie

In your 'Type VII U-Boat Modifications' report you talked about style 6 of the Diesel Exhaust Outlets. Do you have any pictures of this style 6?

Thanks, Simon

[dougie47]

Hi Simon,

Sadly I only have two photos, both of which are terrible quality. I fear these will be no use to you. They are of U 421 in Toulon after a raid by USAAF bombers. They are enough to tell that there was an "exhaust style 6" (as I called it) and the position but not much else.





Westwood has this outlet on page 32 of his Type VII book.

This is entirely typical of late war VIICs - not nearly enough photographic resource materials! 

Cheers,

Dougie

[NZSnowman]

Hi Dougie

Thanks for the pictures and the information. As I hate to see you so upset Here a few more pictures of Style 6 


A good picture of U-348 and U-350 with Style 6. Picture from U-995: Das U-Boot vor dem Marine Ehrenmal in Laboe By Wetzel, Eckard


A very poor picture of U-995 (with its original Diesel Exhaust Outlets - Style 6). Picture from U-995: Das U-Boot vor dem Marine Ehrenmal in Laboe By Wetzel, Eckard

I will keep looking through all my pictures and books, and will post any pictures I found.

Simon

[dougie47]

Hi Simon,

Thanks for the colour photo -very nice.

Cheers,

Dougie

[NZSnowman]

Dougie, do you think the exhaust outlet went through the pressure hull Or did they run the piping down the outside of the pressure hull as low as they could, As there does not seem enough room and I am sure they would not want to add extra holes to the pressure hull. In fact, I believe there not enough room to get same size pipe down that far Maybe they flatten the pipe


The red circle is where I think the outlet is. Does this look OK to you Dougie

 

[dougie47]

Hi Simon,

Yeah, I think the position of the red dot is right. I'm guessing they would not have modified the pressure hull if they didn't have to. Perhaps they ran the pipe as low down as they could, squeezing it between the pressure hull and the hull casing?

Cheers,

Dougie

[Pat]

It seems to be a difficult location but there might be some beneift to it.

PT boats/E-boots/MTB's/MGB's etc. all had a method whereby they could route the exhaust outlets UNDER the water so that they could run silently at night and sneak up closer to the enemy before launching an attack.

Once the shooting started, they opened holes further up above the waterline which made more noise, but let them get more horsepower out of the engine.  Basically, they had been sacrificing power/speed for silence, and then sacrificing silence for speed.

This might explain the reasoning here, although I don't see how they'd open them up when there needed more power (like recharging batteries or surface cruising at flank speed).

[Rokket]

I know the early Gatos had a bazillion PH penetrations, maybe even 2 bazillion (vent risers, various piping, etc.). After some depth charge testing they brought some inside and avoided penetrations when they could, but still had a helluva lot. I agree that any sub designers would be avoiding any not absolutely necessary.

Pat - thanks for the PT info, I always wondered about exhausting under water and benefits/trade-offs.

[Pat]

rokket, my own boat has 7 through hull penetrations below the waterline, and another 5 above the waterline.  Even for a surface boat, through-hulls are a concern and in a marine survey are one of the points that are very carefully inspected.

Yes, the American and British PT's (I'll lump them all together as PT for simplicity) had their mufflers attached vertically on the stern transom.  There were holes at the top with flapper valves that could be controlled from the engine room, and the actual exhaust piles wentdown from the mufflers to vent underwater when they wanted to run silently.

Once the enemy spotted them, there was no longer any reason for stealth so the skipper would call for the flappers to be opened up and the exhaust then went directly out instead of being diverted through the muffler system and vented under water.

When the flappers were open, there might be some visible steam too depending on how hot the engines were, since unlike the closed system of cars, the cooling water was injected into the exhaust flow to help keep the exhaust system cool.

I'm pretty sure U-boats must have also sent the cooling water out with the exhaust the same way and for the same reason.  Subs aren't as likely to want to be quiet since their stealth is by creeping up under water using the electric motors.

[NZSnowman]

For the Type VIIC's there are over 80 pressure hull penetrations. I am sure that the Germans keep the hull penetrations to a minimum but that is still a lot of holes in your pressure hull Here the list of holes for just the Aft torpedo and E motor room.

Aft torpedo- and E motor room

1x For Vent valve for No. 1 main ballast tank
1x Rudder operation
2x Dive planes
2x Propeller shafts
1x Outer torpedo tube door
1x Vent valve for the water tight stern
1x Torpedo loading hatch (clearance 660 mm)
2x For Emergency compartment ventilation intake and exhaust
2x Mine ejection
1x Blowing line for No. 1 main ballast tank
1x Lubrication for No. 1 main ballast tank
1x Hull valve in blow line for water tight stern
1x Sea water flooding line for torpedo tube
1x Ventline for torpedo tube
1x fwd Hull valve for HP air group 1

[Pat]

It's no wonder they leaked all over whenever they were being depth charged.  ("Actung, wasser bomb!!")

Did you have any luck finding a probable opening for the paddlewheel knotmeter?  It's possible there might be one on either side in case one gets damaged.

It seems unlikely, but I suppose it's also possible that they might have just determined the speed by counting RPM of the engine or propeller revolutions, although I'd think they'd still want something more accurate because weather and water conditions could affect speed.

Another question about through-hulls is that there are two openings on either side of the pressure hull near the bow, just slightly behind the planes and about halfway between the planes and the waterline.  They are faired off with a sort of blister over each of them, with the opening to the rear so(probably so that water won't be forced into them by the movement of the boat through the water).  Do you know what these are for?

[NZSnowman]

In original German document it say there are two openings in the pressure hull for the 'Speed indicator'. Does not say which side of the boat. I will go through all my pictures and books again tonight and tomorrow. Will let you know how I go with the search.

[Pat]

On my boat, the knotmeter is located underneath the bilge, just where it turns downward again to the keel.  It's about 1/3 of the way back from the bow, where it would never be exposed to the air even in the most violent storm.

The readout/guage is in the cockpit visible to the helmsman, but of course unlike a sub, I don't have lots of crew to keep track of everything.

Since it's just connected by a couple of wires, it can actually be located a fair distance from the guage.  Mine is about 7 feet between paddlewheel and guage.

[NZSnowman]

Hi Dougie

Was looking through my drawings today and came across a drawing of U-1105 which look like it has Style 6. What do you think?



Also wondering that you think about this:
I was going to extent the stern the flood vents the full length without any gap around the Diesel Exhaust Outlets as U-1308 was commissioned on 17^th Jan 1945 after the 31^st March 1944 order to used Style 6.

Also it look like some boats, just had the Style 6 install (U-348, U-995 & U-1105) but others boats look like they took the time and extended the flood vents between the gap like for U-421.

Also it looks like we could start a list of boats with Style 6.

U-348 (Type VIIC)
U-350 (Type VIIC)
U-421 (Type VIIC)
U-995 (Type VIIC/41) (Maybe )
U-1105 (Type VIIC/41) (Very likely)
 

[dougie47]

Hi Admiral Simon,

I'd concur with everything in your last post. Very likely that U 1105 has style 6. Also your point about taking time to extend the vents I think is correct too.

Good work,

Dougie