[myknowledge]

The double hull significantly increases size and weight.

Larger size and weight is not a major concern for the Russian sub builders, because they believe a larger sub is more survivable.

For example, the Oscar II class SSGN (nuclear cruise missile submarine). Its heavy displacement and double hull enables her to take three direct torpedo hits to sink.

The outer hull acts as an armored shell, much like a turtle shell for a turtle.

[lack-of-trust]

the Russians claim that the “double hull enables her to take three direct torpedo hits to sink”

Has the US Navy ever tested that theory?

I remember in the 80’s the Brits sent an Argentine warship (a cruiser, fromerly CL-46) to the bottom with a pair of WWII vintage torpedos.

[Norman Bates]

If the torpedo hits the propeller the sub will sink no matter how many hulls.

[rmlew]

For example, the Oscar II class SSGN (nuclear cruise missile submarine). Its heavy displacement and double hull enables her to take three direct torpedo hits to sink.

The outer hull acts as an armored shell, much like a turtle shell for a turtle.
The crew of the Kursk may have another opinion.