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NO!...this has been discussed previously; the submerged speed for an extended periscpe needs to be 3 knots or less to prevent tube vibration. AND don't forget to drap your arm over the periscope hand for added steadiness https://www.subsim.com/radioroom//sh...d.php?t=201357

Draping one arm over the periscope handle was a common practice among German U-boat captains, but it wasn't specifically an "Erich Topp thing." This gesture served a few practical purposes:

Stability and Control: By resting an arm on the periscope handle, the captain could stabilize the periscope while making adjustments to its position or while observing. This helped in keeping the periscope steady, especially in rough seas.
Comfort: It provided a more relaxed posture during long periods of observation, which was important during tense situations when the crew was on high alert.
Visibility: The position of the arm could also help in maintaining a better line of sight and reduce fatigue, allowing the captain to scan the horizon for enemy ships or submarines more effectively.
While Erich Topp, a notable U-boat commander, may have been observed doing this, it was not unique to him. Many U-boat captains adopted this practice during their missions.

Also the other factor is going slow to reduce the scope's wake in the water to observant escort vessels : https://www.subsim.com/radioroom/sho...22&postcount=5 https://uboat.net/forums/read.php?20,64127,64136

Originally Posted by walsh2509

he periscope consisted of a long steel tube which extended out to about five meters from the housing. It had prisms and lenses at both ends, for which there was a switch that allowed the commander to toggle the magnification level – either 1x or 6x. Periscopes suffered from two main problems, the most important was vibration. When fully extended, the long unsupported tube created turbulence on a moving U-boat. At 6 knots, it caused excessive vibration which rendered it almost impossible to use. This was dampened by using an extension bracket to reduce the unsupported length and the pointed end was redesigned to minimize the forward hydrodynamic resistance. Nevertheless, vibrations still occurred, but to a much lesser degree. The other problem was fogging of the lenses. Since the damp atmosphere of the U-boat caused fogging, it was especially important that the tube was not only watertight, but was airtight as well. Any fracture on the airtight casing caused by a depth charge attack would result in fogging of the tubes.