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Author Topic: Twin Screw Props.  (Read 2916 times)

wingertaz

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Twin Screw Props.
« on: December 01, 2007, 01:10:44 pm »

I have just been asked this question which I must admit I couldn't answer :embarrassed:.
looking from the stern which way should the props rotate and if they should rotate a certain way? why?

Regards Gary
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catengineman

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Re: Twin Screw Props.
« Reply #1 on: December 01, 2007, 01:17:17 pm »

There has been a very large discussion on this subject within this forum.
If you search prop rotation you may come up with the threads

but basically it is probably down to preference by the owner of the model.

Looking at the props turning out at the top ie PORT = anticlock  STBD = clockwise
that is how they went on three of the tugs I worked on (real tugs)
its how I set up my Tito Neri but the Smit Nedeland ran best with the rotation opposite

R,
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DickyD

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Re: Twin Screw Props.
« Reply #2 on: December 01, 2007, 02:08:09 pm »

On my Robbe Scheutze the props turn in as I found it improves the steering ie from the stern the port turns clockwise and the starboard turns anti clockwise. O0
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wingertaz

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Re: Twin Screw Props.
« Reply #3 on: December 01, 2007, 02:43:59 pm »

Many thanks. I just looked at http://www.modelboatmayhem.co.uk/forum/index.php?topic=4702.0  O0

Regards Gary
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Shipmate60

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Re: Twin Screw Props.
« Reply #4 on: December 01, 2007, 04:05:55 pm »

Gary,
On models with twin screws and single rudder it is better for steering if the props turn INWARD looking from the stern and the top of the prop.
Or
From the stern port prop clockwise, stbd anticlockwise.
This maximises the propwash over the single rudder.

Bob
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wingertaz

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Re: Twin Screw Props.
« Reply #5 on: December 01, 2007, 04:33:58 pm »

Cheers Bob. If it's twin rudder is it still the same.

Gary
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DickyD

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Re: Twin Screw Props.
« Reply #6 on: December 01, 2007, 04:47:25 pm »

It made a difference with mine Gary and it has 2 props and 3 rudders. Really depends where rudders are in relation to props.  O0
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Shipmate60

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Re: Twin Screw Props.
« Reply #7 on: December 01, 2007, 04:49:57 pm »

Its not so crucial for twin rudders.
In general outboard for speed, inboard for maneuverability.

Bob
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Powered Boat Mouldings

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Re: Twin Screw Props.
« Reply #8 on: December 15, 2007, 11:53:00 am »

Hi All
        Agreed with Bob rotate inwards for maneuverability + power, outwards for speed.

Regards Rob.

farrow

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Re: Twin Screw Props.
« Reply #9 on: December 21, 2007, 01:58:32 pm »

Full size vessels with fixed pitch screws always turned outwards, this balanced the steering of the vessel and when manoeuvring enabled the paddle wheel effect of the screws to assist in turning the vessel short ie, 1 engine ahead and the other astern.
With CP/variable pitch propellers, the screws still turn opposite, but commercial ships such as ferries have their 's turning outwards for manoeuvrability. But the RN have them turning inwards, the theory  being that the wash join and make a more efficient and cost saving propulsion to the vessel.
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Powered Boat Mouldings

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Re: Twin Screw Props.
« Reply #10 on: December 21, 2007, 04:42:59 pm »

Hi All
       Well thats sure blown us out of the water :o. I made my statement as this is the way I have always set up my models. Perhaps It works for me because I have either driven two screws through a gearbox one motor, or twin screw with twin motor one speed controller. Never dabbled with twin motors twin speed controllers. Will do one day.

Regards Rob.
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