Surcouf propellers

[Greybeard]

I read somewhere that the Surcouf propellers were not inline, one was forward of the other. Can anyone throw any light on this?

[trout]

Here is a link to plans, it does indeed look like they are not on the same plane. From the rear view the diameter of the props overlap and may be the reason it was done that way.

https://support.caswellplating.com/index.php?/Knowledgebase/Article/View/364/40/the-surcouf-submarine-plans

[Greybeard]

Many thanks.

[Bob Gato]

Great time to clarify this Question in my head-With the propellers offset fore and aft, you would think that the differential thrust would affect the track of the boat...ah, but wouldn't it be possible to offset the thrust bearings to compensate. Is it not so much the placing of the propellers but the placing of the thrust bearings pushing on the structure that determines differential thrust?

[RCSubGuy]

I've yet to have my 48th scale OTW Surcouf on the water, but she has the authentic offset props. I really don't know that the minimal offset would be of notice for something this large, though, as pointed out, there must be some sort of effect, as the props are angled toward the centerline and each would create a slightly different turning moment about the center axis.

I'm going to hypothesize that no effect will be noticeable, but we can certainly experiment once she's completed and taking her sea trials...

[He Who Shall Not Be Named]

I would suggest, to insure a cancellation of any lateral thrust from a two or more shaft running-gear, that all shafts would be toed in so that their respective thrust lines intersect at a common point along the vehicles longitudinal axis. Most ships and submarine see this vector nexus ahead of the c.g. and most who conn these type craft are familiar with the ability to employ differential thrust to effect yaw forces. Those few vehicles with the vector nexus behind the c.g. (type-21 drivers for example) are a special breed, as the same technique is used to yaw the craft -- but it's backwards from the norm.

David

[Kawasaki Monota]

The reason is quite easy: To insure both propellers & shafts are parallelled to the center line of the hull. If both propellers are on the same plane, the propeller shaft will have an angle to the center line, as both shafts are too close to the center line.

Kawasaki

[Albacore 569]

The large 3 bladed props the starboard side is offset forward of the port one aft. the starboard prop is left-handed rotating counterclockwise when viewed from behind. The port prop is right-handed and rotates clockwise The prop shafts as explained above are parallel, and closer. The thrust lines combined are closer to the center line. This should make more noise I'd expect, but the sonar of this period probably would be inconsequential. to distinguish apart but it did allow the prop thrust more concentrated at the center line to flow over the rudder aft behind these props.

Th arrangement was common on French submarines of this period. The Rubis drawings (Saphir class minelayers) are arranged this way tooo. It's a unique feature of French submarines then 1920's to 1940''s.

This practice continued till the Cold War Daphne Class which were separated apart more. the Daphne's were based on the single prop , the 4 Arethuse class subs. The Dauphines were enlarged medium size fleet submarines.

Welcome to French subs...lol







NOTE ON THE SAPHIR CLASS drawing below the Prop OFF SET IS REVERSED! The starboard Prop is offset farther aft in this class. In Surcouf it the Port side.

[gantu]

See here clear shot of the propeller offset.