This is not my field at all, but I know that an earlier collague of mine did some research on a tugboat propeller with ducted tip. His research is published in
Hordnes, I. and Green, S.I., “The Ducted Tip Propeller”, ASME Fluids Engineering Conference, Vancouver, June 1997 (15 pages).
and
Hordnes, I., and Green, S.I., “Sea Trials of the Ducted Tip Propeller,” ASME Journal of Fluids Engineering, Vol. 120(4), pp. 808-817, December 1998
I think Prof. Green at the UBC has done quite a lot of research in this area.