As the propellers go, nobody who knows will tell you.
But on Microsoft maps there was picture some time of Ohio propeller. That propeller was for sure designed for stealth. And it is based on ww2 design, where the tip of the blade is extended back, so it looks like huge 7 bladed swastika.
I have never seen something like this though. Not on any model, any picture, not in any books on submarine design.
But it totally gives sense. Limiting part of the screw is the propeller tip. The tip moves at maximum possible speed (not to cavitate) and the rest of the blade moves slower then it could. The second screw could rotate faster with same tip speed .. and accelerate that not so well used middle part of the propeller disc. It would be something like propeller which tips moves slower then the blades (ultimate dream of any propeller designer).
Also the second propeller could be counter-rotating, which could help even more. It does not look so from the picture, but AFAIK it is DW's limit and DW can't do counter-rotating propellers.
So it would improve effectiveness - it could achieve better acceleration at same power, and it would need less power to achieve same acceleration. That means it could be even more silent.
Sure it would complicate a gearing, I mean a lot.
|