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Author Topic: Submarine Propeller Help  (Read 2715 times)

george

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Submarine Propeller Help
« on: January 06, 2014, 03:43:40 AM »

 Hello

 I have a Two part question for the membership.

 1. What Type / Brand Name / Size propeller would I need for my Darnell Type XXIII ?
 
 2. What Type / Brand Name / Size propeller would I need for my Darnell X-craft?

 Thanks for your help again.

 George

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U-33

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Re: Submarine Propeller Help
« Reply #1 on: January 06, 2014, 06:30:27 AM »

Type XX111...mine has a 50mm three blade brass.
X Craft...mine has a 50mm three blade brass.


Both are Raboesch.




Rich
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Rich

K-157 Vepr. Akula-II (project 971U)
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~~~~~~~  "Motorflotes need love too...."  ~~~~~~~

MotorFlote build log : http://www.modelboatmayhem.co.uk/forum/index.php/topic,15222.0.html

Subculture

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Re: Submarine Propeller Help
« Reply #2 on: January 06, 2014, 10:01:38 AM »

You have a lathe- make your own.

george

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Re: Submarine Propeller Help
« Reply #3 on: January 06, 2014, 11:51:00 PM »

  Hi U-33

 Are they Right or Left hand?

 Hi Subculture
 
 Yes I do have a lathe BUT I am relatively new to metal lathe work. If you were thinking of another how to video, may I request of you a how to make your own brass scale like propeller?

 I know I would download it for sure.

 Thanks Gentlemen

 George

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Subculture

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Re: Submarine Propeller Help
« Reply #4 on: January 07, 2014, 12:06:52 PM »

Prop making has been covered many times over the years. I'm not going to make a video of that.

Here's a good site outlining most of the steps- http://wmunderway.8m.com/cont/prop/prop.htm

If I do any more 'how to' videos, it will be on areas that have had little to no information posted in the past. Sizing endcaps and seals was a big one, and the area that seems to cause problems for a lot of people, so that's why I covered that.

Lathework is a thing you get good at by practice, just like any manual skill, so don't expect first class results the first time you try this.

salmon

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Re: Submarine Propeller Help
« Reply #5 on: January 07, 2014, 03:43:17 PM »

Very nice site, but even though a subject has been done many times each person has their own way of teaching it. How many sites are out there teaching math? A lot. This site starts with " After you have determined the size of the finished propeller, the number of blades and the pitch angle, you are ready to cut metal." We jumped a few steps in the assumption that I know what this just said. How do I determine size of prop, number of blades, and pitch?
I can think of a ton of topics. Sizing motors and props to your sub, brushless motor sizing, figuring out the size of a ballast tank, ....... I could go on and on. You have a great way of explaining things and come from a model submarine background.
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If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

salmon

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Re: Submarine Propeller Help
« Reply #6 on: January 07, 2014, 07:32:45 PM »

I did find an article from an early SubCommittee report, Winter 1992 Issue 11, that describes theory, design, and fabrication written by David Merriman. If you are a member, you might want to look at the back issue. If you are not a member, for $15 you can become a member and get the entire collection of back issues. Talk about a lot of information at your fingertips. There might be other information on props, but this is a good start.
This topic is inspiring me to dig deeper. Might just build a prop for the heck of it.
Andy, you still need to do more videos, just saying. :-)
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If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

Subculture

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Re: Submarine Propeller Help
« Reply #7 on: January 08, 2014, 10:41:31 AM »

If it is a scale model, and you wish to remain as authentic as possible the size and style (blade count, shape etc.) of prop is dictated to you already by the 1:1 version. In the case of very secret modern designs we have to give our best guess e.g. modern propulsors like on Astute and Vanguard.

Assuming we don't have to follow a prototype, then generally speaking a 3-blade prop is usually the best choice for efficiency, with perhaps a two blade for very high speed subs. Larger props are more efficient than small ones, within reason- very large props create a large amount of drag, so there is always a trade off.

With regards to pitch, best efficiency is generally to be found from about 0.8-1.5 times the diameter of the prop, with most props designed for scale electric models tending to be around the area of 1-1.2 pitch.

It would appear that a coarse pitch prop is the best choice, bearing in mind that it will generate more thrust per revolution assuming the same diameter thus allowing a slow revving motor. This is kinder to shaft seals but comes at the expense of generating a larger torque roll effect on the boat, which can be an issue on single screw boats if it happens to have a modest metacentric height for agility. Also coarser pitch props tend to slip more.

In practice, from my own experience and observations of other craft, a pitch ratio of 0.8-1 seems to be about right for model submarines with single screws. Boats with contra rotating screws don't have the issue of torque roll to deal with, so you are free to choose the pitch of your choice.

Subculture

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Re: Submarine Propeller Help
« Reply #8 on: January 08, 2014, 02:00:52 PM »

These are the two books I use as reference for working out propellers.



The larger book on the left is actually for fullsize propeller design, however it is essentially the same, just so long as you remember that model props are a good deal less efficient than fullsize ones. I would say it's of more academic interest than of practical application in this hobby, but I found it an interesting book and learnt a few things.

The book on the right is excellent, and the only type of publication I've seen which deals with model boat prop design. It's takes a very pragmatic approach and is easy to follow, and really covers all the bases IMO.

Sadly it's over thirty years since it was in print, and it doesn't look like it'll go back into print in the future.
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