In the NYGM manual they mention that in real subs the scope was unsuable above about 4 knots as it started to physically vibrate making it unusable - the watery effect is an emulation of this as vibration cannot be modded.
At about 6 knots I think it is, the mod auto-retracts the scope as, again in RL, the scope would be dammaged going above this speed.
The mod essentially now forces you to go slow when using the scope.
