To answer your questions:

1. While the X Plane configuration is very efficient for plane control (it allows the
individual planes to be smaller yet still exert the same control forces) it suffers from several disadvantages from the US submarine design perspective...
Firstly the interactions between the planes necessary to produce turning and
diving movements is complex and needs computer control.At the time Albacore
was built computers had but a fraction of the power and reliabliity that they have now.US Sub design philosophy is to allways have a back up for any system
on a sub.The X plane config does not allow this...if the computer fails,that\'s it... no
backup.Also computers are only as good as their software and how may rev\'s does software need to go through before its totally bug free?
HMS Upholder was nearly lost on trials when the computer controlled main motor
failed after the Captain ordered an emergency full reverse from full ahead.What
happened was that the motor\'s computer system shut the motor down as it thought the motor was malfunctioning.
Also with the X Plane config you cannot reverse a submarine as the planes cannot exert any control whatever for some reason.

2.The counterrotating propellors were adopted as there was not a large enough
electic motor available to handle the power provided by the Silver - Zinc batteries
which were fitted.To handle the power another motor was installed and it drove
a shaft which was wrapped around the original shaft.There was 1 US SSN with
counterrotating propellors USS Jack a Sturgeon class boat.This experiment was not a sucess due to the complexity of the reduction gearing needed and the fact that the counterrotating propellors actually generated more noise than a traditional
single bladed propellor.The sytche shape of modren sub propellors is designed to defeat a phenomenon called \'blade rate\'.This is when each blade of the propellor
passes through the area of disturbed water caused by the subs sail.This would cause the balde to vibrate,and the vibrations would travel up the shaft and into the hull to be radiated into the sea.The curved blades of modren designs enter this disturbed patch of water more gradually..the propellor blades are like a swept back aircraft wing.The Soviets were unaware of this phenomenon for a long time and this contributed hugely to the radiated noise of earlier generations on Soviet subs.One of the Victoe classes was fitted with counterrotating propellors the Victor 2 i think but no modren design uses this form of propulsion.

I hope this answers you query....

Rgrds

Ger W