Question about WWII German U-boat bow planes

I was referring to the FIXED part only!

And the reason is NOT mainly related to net preventing. At least the information at the U 995 a Type IIV C boat in Kiel Laboe says so. That info board was made by ex crew, so I assume that it is correct.

Regards
Richard

 

Gannet, the "dreadnought" reference is for small coastal

U-boats with only two tubes, not what is normally thought of as a U-boat such as Type-VII, which had moveable planes fore and aft, with guards on both.

You can see aft guards on Apex's pic, they also guard the prop.

 

Gannet,

Great post, thanks.

Just an idea, but why not ask the poster who prompted your question?

I don't know the definitive answer to your question but I'm going with

protection, hydrodynamic aid (sometimes a benefit can be had by "slatting"

in front of a hydroplane), trim capability (you thought they might have been

adjustable), stability (snap roll) and perhaps even redundancy to some

extent. That's all I can think of right now.

apex1: Where is the beach photo from, do you know?

Tom

 

It does indeed seem logical that they are guards of some type. Since they are some distance fwd of what is the leading edge of the fin, hence the lift contribution is negligible., other than itself as a lifting surface, since planar.

The use of ballast, is ostensibly for getting down to the depths, by making her 'heavy', or getting to the surface, by making her buoyant. The secondary function is to alter/correct the CoG. The location of the CoG is very important and affects the forward motion and as such influences the effects of the hydroplanes.

The hydroplanes, provide heave and pitch control. They cannot alter the CoG, nor make the sub more or less buoyant for rapid rise and/or descent.

You must remember that a sub, unlike a torpedo, is not axially symmetrical. Consequently the sub has both a force and moment acting upon it about its CoG. Hence these perturbations, vertical, heave, and angular, pitch, are controlled by the hydroplanes.

 

they would have the crew run forward and pitch the forward planes down and use the screws to drive the boat down

 

Knowing nothing about subs but something about sailboats, the VIIC drawing seems to be not really meant as a fin but as a streamlined skeg to support the diving plane. Just like a traditional skeg hung rudder on a sailboat, this would allow a smaller shaft, simpler bearings, and much less reinforcement at the inboard bearing.

The planes also look to have a long chord and be set very close to the hull - even a tiny flexing of the shaft would jam the plane. Perhaps the close fitting to the hull is intended to create an end plate effect to improve the plane's lift.

I've experienced a jammed rudder when a sailboat's spade rudder was bent by a collision with a log. I would expect that a jammed diving plane would be even less fun.

John

 

Having served on submarines, albeit US nuclear missile subs the only thing those projections could be is what John said they are, something similar to a protective skeg, they are to small to have an effect on handling at the submerged speeds at which these boats were capable of (less than 7 knts usually, although some later types could get up to 12) so the actual plane surface angle would have more effect on the attitude of the boat. Even on the boats i'm used to we would only switch to the stern planes when doing "high speed operations" because it would become to easy to over plane at the higher speeds with the bow planes causing a depth excursion. Considering the speeds these boats opperated they would use both bow and stern planes to maintain depth and attitude (bow planes to maintain depth and stern planes to maintain the boats angle).

 

Thank you everyone for your comments

As mentioned by JohnTT, on the Type VIIC U-Boat the fixed fin provided bow plane shaft support, see attachment. However, it is my opinion that this is secondary function because if you look at the Type IXC/40 and Type XXIII it is clearly seen that there is no attachment between the fixed fin and the moveable bow plane.

One thing I notice between German U-Boats and the US & British Submarines is that the bow plane waterline for German U-Boat is lower than the others. In other words, even when running on the surface they would be submerged and therefore would be effective as soon as they were inclined. A thought I am having is that moveable bow plane without a fixed fin would be an abrupt transition whereas with the fixed fin it would be a smooth transition. An abrupt transition would increase the likelihood of over or under control.

Thanks Apex 1 for the great photo and what was written by the crew about the fixed fin primary function not being net preventing.

I wonder if any of the Allies during the war analyzed the German approach.

 

Gannet- you must have been to visit the USS Torsk by now?



I find this passage in G. Williamsons Wolf Pack - The Story of the U-Boat in World War II on use of the forward bow planes:

"Once at the required depth below the surface, the boat would level off and hydroplanes would be used to keep the boat stable and stop it from rising to the surface. U-boats normally had a slightly negative trim, so that if fully stopped they would slowly sink. In order to stay at the required depth, some forward movement was therefore needed and this, in conjunction with skilled use of the hydroplanes, kept the boat level. Although compressed air could shift water fore and aft between bow and stern trim tanks to adjust the balance of the vessel, the simple expedient of moving unoccupied crew members from one end of the boat to the other was often used instead."
http://www.scribd.com/doc/13729308/Wolf-Pack-The-Story-of-the-UBoat-in-World-War-II
This title has many period photos of all aspects of the program.

From what I am seeing the definitive treatise is Rossler's

The U-Boat: The Evolution and Technical History of German Submarines
Expensive...

I think I am gathering correctly that the more important design difference between the two forces is the upper placement of Allied craft compared to the low fins of the German ships?
Functionally the higher planes are not submerged when run on top.

More history this thread- fascinating though also tragic..:

"The attrition rate of somewhere between 70 and 80 per cent is the highest casualty rate of any of the armed services in any of the combatant nations of World War II."

and the "Laconia Order"[/URL]

 

Gannet

Another, in hindsight, rather obvious reason for the fixed "fins" is that image the sub coming along side her berth. It wouldn't be parallel, it would be slightly off, hence the bow would come in first. As such, how does the Capt. know where the ends of the fins are?....the fixed "fins", or rather guards, do just that. Protect the fins from damage when coming along side.

 

Tom there is some text at the picture!!! How would I know about the info board?........:idea:


bntii
got the right hint too:

in case of the German boats that was a pretty noticeable one. As I mentioned above, the bow had no buoyancy, the fixed fin provided a lifting force at the usual surface operation speeds around 10 to 12 kn. The "Tiefenruder" exactly translated "depth control rudder" (what you call plane here), was out of duty at surface.

Thats all I know from a visit in the late 70ies and some talks with former crew.

Regards
Richard

 

Authority

The design studies, of which this report is a part, have been made under the authority of the Chief of Naval Operations restricted letter Op-23C-1-Serial 217423 of 28 May, 1945. This letter directs the Naval Shipyard, Portsmouth, to prepare design studies, perform tests and to compile reports on each type of submarine.

The bow plane guards are relatively heavy horns which are of streamlined section, and extend out and aft away from the hull in a horizontal plane forward of the bow planes, with the extreme end of the horn outboard of the outer edge of the plane, on the axis of the plane shaft. There is no connection between the outer edge of the plane and the end of the horn.

http://www.uboatarchive.net/DesignStudiesTypeIXC.htm

http://www.uboatarchive.net/index.html

 

Richard,

I see no "text at the picture". What info board do you speak of?

I simply asked "Where is the beach photo from, do you know?"

Is it from your personal collection, the Internet, if so where.

I'm sorry if this is too taxing a question for you but I think it reasonable to

ask. Do you know where the photo was taken? Do you know what ship it

is? Let me try and simplify it for you:

Do you have any further information on the photo you posted.

Thanking you in advance for your response regardless of how defensive it

may be.

Tom

 

Hello Tom, no need to loose your good manners.

there is a text above my picture saying that the boat is in Laboe! That is near Kiel (Kieler Woche, Volvo Ocean Race) in northern Germany.
The boat is open to the public and there is a info board aboard (thats two boards).
And the rest was all in my post above the picture! And still is!

I´m not defensive!
Sometimes it would be good to remember that many of the contributors here are not native English speakers, and we are fiddling here with complex subjects (well not in every thread).
Some need about five times longer to type (and often retype) a text than average joe, though their educational level is ten times higher than his!

Hope I could answer your questions sufficiently.

Regards
Richard

 

Richard,

Now I understand, thank you for clarifying.

Regards,
Tom