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TOPIC: Need a screw?

Need a screw? 7 months 2 weeks ago #5484

  • Icare
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Drawing a screw is a daunting task, isn't it? :S But I made it. It's 5 meters wide (~16.5 fts) and has four blades. B)

Well, I didn't use any technical data to do it, but you can use it to make your models looking more realistic.

How to use it?
1. Open the file, EXPORT the screw's layer as a PART file.
2. Open your model's file, IMPORT the screw PART.
3. SCALE it, MOVE it ROTATE IT, modify it as you like.

Notes:

1. The insertion point (coordinates 0,0,0) is at connexion of the shaft's axis and the screw's axis.
2. I made it using an old version of Delftship, I hope it will work with the new version...

Enjoy!
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Need a screw? 7 months 2 weeks ago #5487

  • Maryak
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BZ Icare.

My method has been to draw a screw in CAD, export as VMRL1 file.
Import into DS and save as part.


3BProp.jpg


YeltaProp.jpg


DDGPropMOD.jpg



HTH
Regards Maryak
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Need a screw? 7 months 1 week ago #5493

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But as you can see, Maryak, it's possible to do it using Delftship's software, too.

And now, as it's said in french: "Who can the most can the least": After the four-blades screw, I made a three-blades screw (still using an old version of delftship ;) ).
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Need a screw? 7 months 1 week ago #5494

  • iosif
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Thank you both :)
Especially the 3 blades :)

Best wishes
Iosif
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Need a screw? 7 months 1 day ago #5496

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Yep! The 3-blades screws are more common than the 4-blades.

Now, you have a 7-blades screw... Just in the eventuality of somebody wishing to draw a submarine B)
(It's strange, the file is not bigger meanwhile the drawing is more complex... :huh: )
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Need a screw? 6 months 4 weeks ago #5497

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I have two questions:

1. Why a sub needs more blades?

2. Icare, do you have 2 blades prop also?

Best wishes
Iosif
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Need a screw? 6 months 4 weeks ago #5499

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The blade count has an effect on Underwater Noise i.e. the idea being to reduce pulsation between each blade and thus the amount of noise generated, particularly at low propeller revolutions as this usually when a submarine is at its most stealthy and is harder to hear coming or going.
The requirements to keep the reactor cooled in Nuclear boats means they generate more noise than a battery powered (Conventional) boat. The latest French design is a pulse system where the propeller is inside the hull and draws water in and out through a duct. Cavitation and accoustics are theoretically reduced compared to a conventional external propeller.
HTH
Regards Maryak
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Need a screw? 6 months 4 weeks ago #5500

  • tegolf
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Hi iosif.

I am a retired submariner, so I may be able to answer your question, though I'm not a marine engineer.
For a given thrust, more blades allows you to reduce shaft rpm. So during the development of the modern submarine propellers, it was not uncommon to see five- or six-bladed propellers. Early subs, due to their limited number of shafts, required much higher shaft speeds than modern boats to attain the required speeds.

However, other factors contribute to propeller design and the number of blades. The larger the blade diameter for a given shaft rpm, the higher the blade-tip speed, and thus the more likely tip cavitation will occur. Since subs rely on acoustic stealth, cavitation is avoided at all costs with submarine propellers. This is one of the reason the previous generation of subs had large, highly-swept, low-pitch screw blades.

Finally, the prime-number of blades is a trade-off on maximizing propulsion, taking the other factors into account, and limiting the generation of certain acoustic signals that permit classifying the vessel as a submarine. Going any further than that gets into classified information. Virtually all the major nations with subs today use 7-bladed screws. The next generation of boats are moving to ducted thrusters, to further reduce radiated noise.

Below is a model I made of a 1980s-vintage SSN propeller, using Blender.

Blender7-BladedProp.jpg
Be very, very careful what you put into that head, because you will never, ever get it out.
Thomas Wolsey
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Need a screw? 6 months 4 weeks ago #5501

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Thank you both Icare and Tegolf

Best wishes
Iosif
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Need a screw? 6 months 3 weeks ago #5508

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As far as I remember, I never saw any 2-blades screw except on toys, however I know they exist... with folding blades (The blades unfold when required due to the centrifugal force). But it isn't the point of this topic. I offer you only decorative screws.

Here you have one, Iosif, but I ain't satisfied with its look. There's something odd. I'll try to draw an other one as soon as possible.
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