WWII German U-Boat Bow Planes

Very interesting. I imagine the location of the bow planes was due to experimentation and evolution. It may have been a way to reduce the time it took to dive to avoid detection. The longer a boat stayed on the surface, the more vulnerable it was to detection and attack. They may have been trying to utilize forward motion to aid in diving, but I think the main reason was for a quick dive.

Your comment about being able to dive quicker is a very interesting point.

I have to think the Allies would had analyzed the German U-boat design approach; however, I cannot find anything.

Thanks Again

in the absence of sophisticated Under water detection system during WW2 the argument of quick dive sounds logical.

crm

Not quite true.

I believe in late 1943 the complete "Squid" system came into usage in the RN and the German U-Boats had as a result a hard time escapimg, you will find (if I remember correctly) that from 1943 onwards, detection and anihilation of U-Boats took a dramatic turn for the better (Allies point of view).....

From 1942 the Hedgehog was in usage but was not quite as good as it needed contact, whereas the Squid exploded at a programmed depth.

The main fix was that the U-Boat could be "seen" underwater and as the Hedgehog and Squid bombs were fired to a point, ahead of the ship, allowing the Sonar to still "see" the target. The Squid had a mid range of 375 yards. Therefore the attacking ship did not need to sail over the sub (which often turned away sharply at that point as the Sonar of the time could not look directly downwards....

I had colleagues with Hedgehog experiences that were downright dangerous. I also looked after a 6 barrel Squid system on HMS Puma in the 60's it worked very well and was extremely accurate.....

The Mark 10 Mortar which came later used the same bombs, bur without cables for depth setting, they used a type of hypodermic needle instead.....reloading was much easier and relatively dry as the loaders could stay under cover!!! Bomb Range was vastly improved and was variable too....

Good sources of far more detailed info can be found here and here.

I believe you already said it.

The fins are oriented in a slightly downward angle so that the slight positive buoyancy of the boat is negated by the fin directing the boat downward. That means you won't need so much adjustments on the bow planes to keep the boat at an even keel.

Next, when you need to make a fast dive (to escape detection or evade depth charge), the downward orientation of the fixed planes adds to the downward orientation of the bow planes allowing the boat to dive more steeply. Going deep is a boat's best defense.

regards,

Vulcan

My opinion is the the forward part was to protect the movable plane from getting snared on a cable. You'll see the wire from the bow to the conning tower serving the same purpose.

Exactly what I was thinking; you beat me to the comment.

Thanks everyone for your comments.

I cannot believe how this question has taken over my life.

I am asking this question both here and at http://www.boatdesign.net/forums/boat-design/question-about-wwii-german-u-boat-bow-planes-29813-2.html

It was brought up that 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.

Another thing I notice that on US and British Submarines their bow planes were above the waterline when on the surface; whereas, the Germans U-Boats bow planes were below the waterline then on the surface.

The following are the applicable excerpts on Diving Planes from Friedman, Norman; Submarine Design and Development; Conway Maritime; London; 1984; pp122-126:

• Diving planes perform three very different functions; diving, surfacing, and depth and trim control. The latter must be quite precise at or near periscope depth.
• At greater depths, it is more important for maneuvering, so that the rate of changing depth is more important than the ability to maintain a particular depth.
• Bow planes located underwater (when the submarine was fully surfaced) would be effective as soon as they were inclined, and so would (in theory) make for fast submergence, but they were also a source of resistance, making for reduced surface speed. Planes above the waterline would not slow a submarine, but they would not take effect until it reached the awash condition; i.e., until some considerable flooding had occurred.
• Bow planes were also notoriously subject to damage when coming alongside or docking. One compromise was folding planes employed by many navies. However, it was argued that the extra mechanism increase their chance of failure.

On the latter bullet, it is my opinion that the fixed fin wouldn't provide enough protection from damage and would still require repairing the bow planes.

The following link is to Design Studies done on German Submarines. They actually call them "Bow Plane Guards"

"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."

Another thing I notice is the German WWII submarines had their bow planes always submerged even when the sub was surfaced; whereas, the US and British submarines bow planes were either at the waterline or above the waterline when not retracted. From what I had read this was done by the US and British to reduce drag while running on the surface

One thing I noticed in the design study is that on the Type IXC-40 the bow planes are rigged at a 7 degree rise (design was for a 5 degree rise) and because it is submerged while the submarine is running on the surface would provide lift such that it would reduced wetted area. I am thinking that the reduction in skin friction drag maybe significant enough to offset the drag associated with the bow plane being submerged.