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Author Topic: Normand Oceanic -weird prop set up  (Read 1558 times)

Brian60

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Normand Oceanic -weird prop set up
« on: March 03, 2017, 03:11:34 pm »

OK so I was on my favourite offshore page today and this photo was posted. Look at the two outside screws, its easier to make out on the starboard one, there are two contra rotating blades.

Now, wouldn't they work against each other considering their profiles?

gingyer

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Re: Normand Oceanic -weird prop set up
« Reply #1 on: March 03, 2017, 03:14:05 pm »

Aircraft such as the fairey Gannet  russian Tu-95 bomber used to have contra-rotating props.
they produced more thrust and stopped torque rotation.....
lots of torpedoes were fitted with contra-rotating props too  :-))
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Brian60

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Re: Normand Oceanic -weird prop set up
« Reply #2 on: March 03, 2017, 03:32:31 pm »

It just seems to me that having them that close together all you are going to do is produce a lot of cavitation between the blades. I've seen similar but on opposite ends of the azimuth pod, so that there would be 3 metres or so between the blades, but these are so close

gingyer

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Re: Normand Oceanic -weird prop set up
« Reply #3 on: March 03, 2017, 03:36:25 pm »

I am no designer but on aircraft and torpedoes they are only inches away from each other......
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John W E

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Re: Normand Oceanic -weird prop set up
« Reply #4 on: March 03, 2017, 04:04:43 pm »

here you go Brian some interesting reading about contra-rotating props :-)

http://www.joules-project.eu/Joules/technologies/consumption_propulsion
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JIM WORNER

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Re: Normand Oceanic -weird prop set up
« Reply #5 on: March 03, 2017, 05:06:33 pm »

If you think on it, the fluid flow from the leading prop will be accelerated onto the second prop, which uses the acceleration to increase output. Always assuming that the first prop is not cavitating.
On aircraft with contra props and 2 engines (Fairey Gannet, Bristol Brabazon) you could shut down one engine and feather it's prop for economic cruise.
PS I have just read the last sentence and realised how old I am, (I watched the first flight of the Brabazon as a lad!)  Heigh Ho.
Cheers
Jim {:-{
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dougal99

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Re: Normand Oceanic -weird prop set up
« Reply #6 on: March 03, 2017, 05:35:04 pm »

Ah! Jim but inside your still a lad  :-))
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Brian60

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Re: Normand Oceanic -weird prop set up
« Reply #7 on: March 03, 2017, 08:09:28 pm »

here you go Brian some interesting reading about contra-rotating props :-)

http://www.joules-project.eu/Joules/technologies/consumption_propulsion


Interesting read. A payback of 7 - 10 years for the technology :embarrassed: a lot of these ships are being scrapped at the moment with less years on them than that.

JIM WORNER

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Re: Normand Oceanic -weird prop set up
« Reply #8 on: March 04, 2017, 03:29:55 pm »

Just a final thought, on single seat  aircraft the main reason for contra props was to reduce the propeller disc diameter, hence shorter undercarriage. 
I wonder if the same applies to a ship?  Letting it work in shallower water?
Cheers
Jim {:-{
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ballastanksian

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Re: Normand Oceanic -weird prop set up
« Reply #9 on: March 04, 2017, 11:27:48 pm »

What is she Brian? That implement on the stern in yellow looks very big. I am wondering if the contra prop arrangement is for quick response in geostationary positioning roles?
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DavieTait

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ballastanksian

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Re: Normand Oceanic -weird prop set up
« Reply #11 on: March 04, 2017, 11:59:07 pm »

That's a lovely looking crane. Any model of it would need lots of stuff on deck to make it visually interesting, though the crane detail would be a serious project in its own right.

Thanks David  :-))
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derekwarner

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Re: Normand Oceanic -weird prop set up
« Reply #12 on: March 05, 2017, 12:13:41 am »

The American DDG51 Airleigh Bourke Class destroyers traileded contra rotating propellers >>:-(  during a Hydrodynamic underwater assessment trials
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