prop thrust enhancement, tubes

[trilight]

I am hoping to power my big trimaran with several high thrust 9.9 4 strokes. I have seen and read of short tubes which are mounted around the props of tugboats to enhance the thrust, I believe they are formed with a hydrodynamic foil cross section. Any experience with these devices, I have also seen them on outboards. Thanx

[boats.net]

No I haven't had any dealings with them.

[robert graham]

I've seen those metal rings around the props on special boats, but maybe they're more for steering thrust/control and prop protection than actually increasing thrust? There are protective metal rings that can bolt on a lower unit to help keep weeds and grass out of props...maybe that's what you're thinking about?