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>> Home > Forum > Any Other Questions! > Counter Rotating Props
Counter Rotating Props
(1467 views)
Author Message
none
(Fleet Admiral!)





Forum Posts: 185
1st Apr 2017 10:29  
>> Permalink
mdlbt.com/27179

Counter Rotating Props when fitting do they both go outboard or inboard when rotating.

Not ready to do this yet it is just a question I need to know for later...

Commodore-H
(Sub-Lieutenant)





Forum Posts: 13
1st Apr 2017 16:47  
>> Permalink
mdlbt.com/27187

Props






Props




Props turn outward

Commodore-H
(Sub-Lieutenant)





Forum Posts: 13
1st Apr 2017 16:48  
>> Permalink
mdlbt.com/27188

Make sure they are opposite pitch:-)

none
(Fleet Admiral!)





Forum Posts: 185
1st Apr 2017 17:48  
>> Permalink
mdlbt.com/27191

Many thanks for the the information

4clubs
(Fleet Admiral!)





Forum Posts: 102
1st Apr 2017 18:07  
>> Permalink
mdlbt.com/27192

They are CONTRA not COUNTER rotating and on LIFEBOATS they turn inwards on other vessels they generally turn outwards when the vessel is in the forward direction.


maxferrie
4clubs
(Fleet Admiral!)





Forum Posts: 102
1st Apr 2017 18:27  
>> Permalink
mdlbt.com/27195

CONTRA AND COUNTER rotating Props . Actually both are correct.
Probably counter rotating is more correct for ships.
We could argue for days!! Anyway they both go in different directions. One clock wise when the other is anticlockwise, but make sure they have left and right hand props, not the same type or you will be in trouble.


maxferrie
Dave M
(Fleet Admiral!)





Forum Posts: 1348
2nd Apr 2017 22:32  
>> Permalink
mdlbt.com/27219

Actually for ships with props on separate prop shafts it's counter rotating.
Contra refers to aircraft equipped with contra-rotating propellers with rotation about the same axis in opposite directions. Contra-rotating propellers should not be confused with counter-rotating propellers on separate shafts turning in opposite directions.
I was intrigued by this discussion, possibly because it reminded me of my model flying days.
What would we do without Wiki!
Dave


Live long and prosper

Dave
pmdevlin
(Fleet Admiral!)





Forum Posts: 315
2nd Apr 2017 23:11  
>> Permalink
mdlbt.com/27220

with my 4 foot fireboat, I use contra rotating props, from propshop. I was advised by them to have them turning outwards, as viewed from the rear, there was an explanation, I've forgotten it, however, on the water, at speed, turning was difficult, the boat just wanted to roll. I swopped them over, so turning inwards, and the handling was cured in an instance. Its easy enough to try one way, then the other, see what is best for you, but remember to use some sort of none permanent thread lock or you might lose one of your props

RNinMunich
(Fleet Admiral!)





Forum Posts: 1015
19th Apr 2017 22:49  
>> Permalink
mdlbt.com/27622

Hi from Munich,
basically if you have two props and only one rudder you want to get maximum force (i.e. water pressure) on the rudder. Therefore the props should turn inward to concentrate the flow over the rudder. The Admiral's experience confirms this!! My own experience with a 1:72 scale H Class destroyer (136cm) was the same. 😉 Cheers Doug 😎


"Retirement is when you stop living at work -
and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
Trillium
(Commander)





Forum Posts: 65
20th Apr 2017 21:40  
>> Permalink
mdlbt.com/27630

Inwards or outwards - should the props be turning to meet together above the shaft or below it?

Also from Wikipedia "Contra-rotating is where parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes non-coaxial propellers on separate shafts; one turning clockwise and the other counter-clockwise."
Torpedoes are a marine example of contra-rotating props.
Roy

RNinMunich
(Fleet Admiral!)





Forum Posts: 1015
21st Apr 2017 12:35  
>> Permalink
mdlbt.com/27634

If they're turning inwards they (or better the water flow) 'meet' above the shafts, conversely: outwards = below the shafts where it disperses more easily, and probably also mostly below the rudder 🤔 Of course the hull form at the stern plays a major role. Which is why most modern fast naval vessels have a relatively flat hull at the stern if the only have one rudder. (Spent the last 31 years designing integrated COMMS systems for naval ships so have seen several such plans and GAs and many ships during the build.)
With two rudders (1 per shaft) it's different. Classic example RN vs KM 1935/36 destroyers in WW2: RN 2 shafts 1 rudder; KM 2 shafts and 2 rudders. Giving them much better rudder response & manoeuvrability.
Your comment re Contra is spot on 😉 Cheers from Munich.


"Retirement is when you stop living at work -
and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
reilly4
(Lieutenant)





Forum Posts: 6
22nd Apr 2017 01:01  
>> Permalink
mdlbt.com/27649

An excellent discussion with very valid arguments. I have always had my twin shaft/prop vessels with outward turning propellers, but I will now reverse one of them to inwards turning to see how much difference it makes. Always learning...

Trillium
(Commander)





Forum Posts: 65
22nd Apr 2017 03:30  
>> Permalink
mdlbt.com/27650

Now here's a question for the experts.
I have two identical waterjets for fitting into a model; same size and same rotation for forward motion.
Will I see the same effect as if I had two open water props which were the same?
Roy

Dave M
(Fleet Admiral!)





Forum Posts: 1348
22nd Apr 2017 10:26  
>> Permalink
mdlbt.com/27653

Simple answer is no as they use a totally different way to provide power.
Water jets suck water into a tube and eject a high pressure jet of water. My water jets have a steerable nozzle to control the direction of the water jet and a bucket to reverse the flow for reverse, exactly the same as on the full size Shannon lifeboat.
You will see a much greater speed using water jets as they are optimised for high performance at the design stage.
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1015
2nd May 2017 01:01  
>> Permalink
mdlbt.com/27973

Not much more to add is there ? 😉 Just ...
I once had the experience to be on board a navy Fast Patrol Boat (AKA FPB) for sea trials. She was waterjet powered and went like s... off a shovel 😉 Only problem; she was hard too keep on a straight course 🤔


"Retirement is when you stop living at work -
and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
reilly4
(Lieutenant)





Forum Posts: 6
2nd May 2017 05:35  
>> Permalink
mdlbt.com/27979

The US Navy Arleigh Burke class destroyers have outwards rotating propellers and the Ticonderoga class cruisers have inwards rotating propellers, so nothing definitive to be learned there.

RNinMunich
(Fleet Admiral!)





Forum Posts: 1015
2nd May 2017 09:51  
>> Permalink
mdlbt.com/27980

Hi downunder, might be interesting to compare the hull shapes!? 😎
Could give a clue.


"Retirement is when you stop living at work -
and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
RNinMunich
(Fleet Admiral!)





Forum Posts: 1015
6th May 2017 08:12  
>> Permalink
mdlbt.com/28180

Hi Reilly, both ships have twin rudders, one per screw, so the direction of rotation hardly matters. See also ma comment re KM 'Narvik' destroyers.
Cheers 😎


"Retirement is when you stop living at work -
and start working at living!" i.e. boat modelling!" 舰队的海军上将 😉 Doug
Delboy
(Chief Petty Officer)





Forum Posts: 20
10th May 2017 22:07  
>> Permalink
mdlbt.com/28596

Sorry to be pedantic but I do like to be specific. Counter rotating props will always be turning inwards whichever direction they turn.

I am assuming (!) that turning inwards in this context means that, seen from aft looking forward, the port screw is turning clockwise and the starboard screw is turning anti-clockwise.

Correct or no?

pmdevlin
(Fleet Admiral!)





Forum Posts: 315
11th May 2017 00:05  
>> Permalink
mdlbt.com/28608

no, they can turn outwards or inwards, as per my previous post, its trial and error whatever suits that application, its an easy job to swop them over, and just try it, by just swopping them over left to right, and reversing the motors. The blades just have to turn the correct way to drive the boat forwards

epmbcmember
(Chief Petty Officer)





Forum Posts: 14
12th May 2017 22:18  
>> Permalink
mdlbt.com/28759

I have always know propellers as left or right handed and on a single screw ship they nearly always turn clockwise looking from aft. Can be very handy if you know which is which as when approaching a berth on the port side at an angle with a right handed prop a good kick astern will put you flat alongside if you time it right. Done it many times with the real thing on all sizes of vessel. Can very often upset the Captain!!!
but if timed right it works a treat.

onetenor
(Fleet Admiral!)





Forum Posts: 166
13th May 2017 22:12  
>> Permalink
mdlbt.com/28817

Experiment is my suggestion to see which suits your boat best. Goodluck👍