ducted or shrouded props need 2 things
they need to be very close tolerance fit prop tip to duct
and the prop diameter changes as thrust characteristics differ
more usually, higher thrust, therefore higher blade loading per smaller area prop disk

it was offered to Collins boats as a variation
the knowledge on hand suggested the noise would be greatest as a 45 degree azimuth from the rear of the duct, but much lower everywhere else

but it would also prevent much unstable blade loading while near the surface
meaning significantly higher efficiency in the transmission of available power
and less wear on bearings and drive due to unequal thrust

for those who wish to experiment,fine
but I would think that after out experiences with 471 working with available technologies in outboard props would be more trouble free and cheaper, because ultimately outboards are well sorted designs for all seas use.