Ford's answers to the NHTSA 6.7 Investigation

BenK wrote:
Also remember the Toshiba issue where they were caught selling sub prop secrets

ALL of my systems on the floor, in WIP, fielded, etc had to have all of their
components removed and replaced...

Mainly my military stuff, but the corporate stuff likewise but not a 100% remove
and replace mandate

I loved COTS, as it allowed to NOT have custom part numbers, assemblies, etc

Basically, the fluid dynamics that led to the design is to delay the velocity of fluid flow as one extend out from the center, and by slowing the velocity with the sweep back, slow down the onset of the "bubble point" where vacuum is pulled --- the collapse of which causes the bubbling sound and also ablade the surface (cavitation).

There are, a bit more tricks to the design, include the use of multiple materials to reinforce the device internally and to cast the outer parts around the skeleton, and to not have it come apart under the normal stress.

However, the core reason for the phase out is not that the knowhow is now.... public, but the use of a large shaft with considerable rotating mass, and as such, it is nearly impossible to not have some vibration which, even dampened, emits noise. Shaft failure from a nearby explosion or bending is also a major weak point for vessels.

Then there is the issue of the prop itself, which given its shape, is an excellent reflector that is omnidirectional, making it relatively easy for an active pinger to bounce a signal off it even if its radiated noise is relatively low.

Hence, current designs now is to gradually get the big shaft and props out, put the prop into s propulsor that is ducted, with the outer duct coated and made of flat surfaces to address active return.