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[rathikrishna]

Friends..i told you all that i am going to make one craft with three screws...but now i am going to make a craft with CONTRA ROTATING PROPS...is it possible with such a configuration in water...?   any advices... please...

[Shipmate60]

Rathi,
Most models with 2 shafts have them running in opposite directions.

Bob

[Mankster]

Perfectly possible, losts of model subs (and torpedos) have been built with contra rotating probs. Use a gear box or two inline motors (you have to replace 1 shaft with a hollow one). Not sure why you would wan to do it in surface boat though.

[Shipmate60]

Rathi,
Do you mean 2 props on each shaft contra-rotating or the props rotating different ways with the shaft?

Bob

[HS93 (RIP)]

if they are on ons shaft hear are some ideas if its a small boat

Peter


http://www.pt-boat.com/torpedo/torpedo.html

[rathikrishna]

Yes..friends..i want to make a craft, with contra rotating, means, two props rotates in oppo: directions on a same co axial shafts...i hope it will give me more speed and tourque...is it...?..or a waste effort...?  please..

[andrewh]

rathikrishna

Good for you!  This is quite common in aircraft, and as Mankster says, submarines.

The props will rotate in opposite directions and (if water is anything like air) the second prop that the water comes to (the rear one) will need a much higher pitch than the front one.

The reason being that the first propellor gets a cylinder of water moving backwards, but also rotating and the second prop has to work in this "screw" of water

However don't worry about theory - try it and tell us of your trials, success and things you learned on the way

I am making a contra-prop for an indoor R/C aircraft (a semi-scale supermarine Seagull)

andrew
PS - liked your puffer

[rathikrishna]

Oh..god you are making a seagull...nice...it will work nicely..i done one westland wyvern once..still it works nice..but i lack fuel here in my native...good luck..god may bless you...