Caged propellers

[kistinie]

A fast multihull like Provu a F40, is motoring 4/8 Knts with an electric or ice motor, but will sail up to 30 Knts, 15/20 being most common

Of course a VPP is THE solution but i do not think such prop is available for power under 10Kw, and price I'm afraid is stratospheric

With such a variation of speed, propeller will be bad on on side of use.

Can a ducted prop, under pitched be an help for low speed, bringing less total drag and vibration at very high speed ?

[FAST FRED]

With a kort nozzle there is no need for 10% or 20% tip clearence.

The ring can be at the hull bottom.

10% down angle is 10% loss of efficiency FOREVER!

FF

[jehardiman]

FF is correct; build the nozzle into the hull to increase the wheel size as much as possible and for a 1.2m wheel I would make tip clearence no more than 1-2mm on a kaplan bladeform with a real good dynamic balance.

[Landlubber]

Yes thanks fellas, I realise the nozzle prop has very littlke tip clearence, I actually work in a shipyard at present, but being Chinese, it is very hard to get anyone there that knows anything to be able to communicate effeciently.

That is why I asked the world at large, I see kort nozzled tugs and workboats, but very few freighters with nozzles.

I do tend to think that a fine sectioned section could certainly improve general performance as our top speed is 15-16 anyhow, and certainly do not expect to be doing that sort of speed much as it cost more than double a nice cruising 10 knots.

Thanks so much for all your comments

[DMacPherson]

"Contributions of a nozzle in ducted propeller performance"

[Landlubber]

Thanks Mac, short and sweet, but certainly interesting info.