Periscopes

[Maverick30]

In real life the kaleun used the periscopes at submerged high speeds (ex: 7knots above)? The periscope didn't suffered from high vibrations caused by hydrodynamic resistance?

[JScones]

Periscopes were fitted with "helical rods" (or "helical wires") that broke the water flow into general turbulance so as not to create any resonating eddies in the water (more on what an eddy is here http://en.wikipedia.org/wiki/Eddy_%28fluid_dynamics%29).

Note that this did not fix the vibration of the scope tube itself, just the conical part. The vibration in the scope tube was removed by adding an extending bracket which increased the tube's natural resonant frequency.

Some examples:

http://img529.imageshack.us/img529/5685/image2nx8.gif
http://img529.imageshack.us/img529/3726/image3sd7.gif

[Maverick30]

Periscopes were fitted with "helical rods" (or "helical wires") that broke the water flow into general turbulance so as not to create any resonating eddies in the water (more on what an eddy is here http://en.wikipedia.org/wiki/Eddy_%28fluid_dynamics%29).

Note that this did not fix the vibration of the scope tube itself, just the conical part. The vibration in the scope tube was removed by adding an extending bracket which increased the tube's natural resonant frequency.

Some examples:

http://img529.imageshack.us/img529/5685/image2nx8.gif
http://img529.imageshack.us/img529/3726/image3sd7.gif

Thanks for replying, now I understand :)

[Brag]

Excellent question and fantastic reply. One learns something new every day :D

[geosub1978]

In the type XXI submarines there was a switch which automatically lowered the masts including periscope at speeds > or = 9kts because the vibration was imposible to be removed. That switch could be ON / OFF / SURFACE MODE.

[_Seth_]

In the type XXI submarines there was a switch which automatically lowered the masts including periscope at speeds > or = 9kts because the vibration was imposible to be removed. That switch could be ON / OFF / SURFACE MODE.

True!:yep:
(IIRC, all schnorkel-equipped subs had "speed limits", so that the strain from the water would not break the equipment.)