What is periscope depth?

[Rick Teskey]

What is periscope depth?
Is it the maximum height a scope can reach above calm seas?
Do they take swells into account ?
As a ball park, what would that be 50-60 feet? Is it measured from the top of the sail or the keel?
Just wondered.

[Slats]

Probably depend on the specific class of boat.
Nonetheless, that's a great question. I have often wondered what the PD depth meant especially in terms of where the scope was (how far it was out of the water) at PD?
J

[greenman407]

Not that my word should be considered the last word but I would say the depth specific to each boat where the periscope functions as a compromise between calm seas and rough.

[NavyICman]

Depending on the class of boat, that depth at which the optics of the scope are clear of the water in a sea state zero to one, with the scope fully extended.

[He Who Shall Not Be Named]

... as measured from the keel of the boat.

The keel (bottom of the hull proper) is the datum line for all boat depth measurements.

David,

[greenman407]

Yeah! What he said.

[He Who Shall Not Be Named]

With the scope up, in rough weather the OOD would instruct the Diving Officer (the Dive) to bring the boat up a bit so the scope head would spend less time in the swells. The command from the stand might be a simple, "Bring it up a bit will ya", or the more formal, "Diving Officer, make your depth ---- feet!".

[639mpa]

It is the keel depth with the scope just out of the water fully extended on calm seas. On the Tautog it was 69.5 feet. Ship handling at periscope depth was mostly done with seas abeam the ship especially in rough weather. If the waves were from the bow or stern direction, the ship tended to pitch alot and depth keeping was very difficult. This made the periscope either too high or submerge making the CO or OOD pretty upset. One night in the NORTH Pacific I was the OOD when we came to Periscope depth in rough weather We kept the seas abeam to control pitch but we rolled so far that one moment I could see the phosphorescence in the water from biologics and the next moment I was looking at stars. This continued the whole time we were at PD. It is among some of my favorite memories. Lot of the crew got sick. On that same trip we took 20+ degree rolls at 400 feet. The ocean is very violent up there in the winter.