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Author Topic: Propellers  (Read 2035 times)

tugger

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Propellers
« on: October 22, 2009, 09:43:07 PM »

what is the benefit of using a 4 blade prop over using a 3 bladed one?
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craftysod

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Re: Propellers
« Reply #1 on: October 22, 2009, 10:18:29 PM »

A four blade prop provides more thrust than a 3 blade.
That is why tugs and boats that require power but not speed use them.
For fast boats they use 2/3 blade,because they spin faster for more speed.
The pitch and blade design play a big factor to what the boat in question requires.
Hope that helps
Mark
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Martin [Admin]

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Re: Propellers
« Reply #2 on: October 23, 2009, 05:49:44 AM »

You can also user smaller diameter 4 blade than a three blade and still get the same amount of thrust.... in theory!
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richo

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Re: Propellers
« Reply #3 on: January 22, 2010, 02:21:27 PM »

I am building a PBM County class destroyer kit from the 70's but have misplaced one prop and shaft. Need to get a pair of brass(or nylon) 1" dia props with 2mm shafts 175mm long.
What I want to know is with twin props, do they need to be opposite(left and right hand) and which way do they need to spin (with the blades coming up in the center or going down)?
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Martin [Admin]

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Re: Propellers
« Reply #4 on: January 22, 2010, 02:48:53 PM »

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rsm

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Re: Propellers
« Reply #5 on: January 22, 2010, 03:24:58 PM »

Hi richo,
I would contact George Sitek  (www.gsitek-props.co.uk) as he manufactures a complete running set for the county class destroyer in various scales and may, therefore, be able to do one for your kit and answer your questions. He's very friendly and his work is first class.  :-))
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Mark47

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Re: Propellers
« Reply #6 on: January 22, 2010, 07:09:11 PM »

I am building a PBM County class destroyer kit from the 70's but have misplaced one prop and shaft. Need to get a pair of brass(or nylon) 1" dia props with 2mm shafts 175mm long.
What I want to know is with twin props, do they need to be opposite(left and right hand) and which way do they need to spin (with the blades coming up in the center or going down)?

It's better to have them turning in different directions, never tried both the same way but I believe they will cause the ship to list to one side if same. As a rule of thumb, turning downward will give better maneuverability. Although long slim models may not be able to turn at full speed with this configuration if they are top heavy.

Hope this helps. :-))
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Perkasaman2

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Re: Propellers
« Reply #7 on: January 22, 2010, 07:35:38 PM »

Twin props are best when they are 'handed' and should spin outwards rather than inwards  - looking from the stern forward.... LEFT PROP ANTI CLOCKWISE and RIGHT PROP CLOCKWISE for optimum power and neutral steering/handling. This arrangement is considered optimum in efficiency since wasteful  side thrust from either of the props is cancelled/minimed.  :-)
We are spoilt for choice with brass prop choices but 'The Prop Shop' produce superb, highly efficient, smaller size props and it's worth paying extra for their performance. Link below - researching their site is well worth the time spent.  ok2

http://www.prop-shop.co.uk/index.php?id=37&section=store&sub_section=products&product_type=37
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richo

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Re: Propellers
« Reply #8 on: January 24, 2010, 03:20:22 AM »

Thank you all for your advice, help & comments.  I found a length of brass rod at the Hobby Habit store near me and the suggestion was to use the prop I have as a template and cut a second one from sheet brass.
The prop will be soldered to the shaft and then the 40 year old PBM destroyer will sail the seven seas (local lake).
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