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Author Topic: Twin prop direction  (Read 2416 times)

1275mini

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Twin prop direction
« on: June 06, 2018, 07:58:26 PM »

Ok lads we seeem to have sorted the main drives !
Thanks very much
Next question useing twin props do they have turn counter directions left and right as I am about to order a couple of 4 bladed props why best size to order ?


Have returned to model boating after quite a few year last I was boating it was multi racing I did with comb 90 engines
Spent most of my time after that with large helicopters nitro petrol and turbines
So scale boats are nearly new to me last one I built in the 70s was the Elke
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Fastfaz

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Re: Twin prop direction
« Reply #1 on: June 06, 2018, 08:35:08 PM »

Re prop rotation they need to turn in opposite directions i.e. Looking from the stern forwards the left hand/port prop should be rotating clockwise, right hand/ starboard prop rotating anti clockwise. This is the method that I use on my tugs, you will need a matching pair of props 1 left hand 1 right hand.
     I always use Simon at Protian props (Propshop) he has now set up on his own and makes great props. Regarding prop size of depends what you are going to be doing with your boat, most tugs if used for towing will have 70mmm 4 blade props usually in Kort nozzles.
    Hope this helps.
          Cheers, Pete.





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1275mini

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Re: Twin prop direction
« Reply #2 on: June 06, 2018, 09:46:20 PM »

Looks like they closed down


http://www.prop-shop.co.uk/
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KitS

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Re: Twin prop direction
« Reply #3 on: June 06, 2018, 10:06:07 PM »


Looks like they closed down

http://www.prop-shop.co.uk/


Well that's a pain, for them and we customers too.

The only winners are the insurance people, naturally...........  :((
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Regards
Kit

raflaunches

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Re: Twin prop direction
« Reply #4 on: June 06, 2018, 10:13:08 PM »

Thatís the old company bought by Swan Morton that made a hash of it, Simon Higgins continues as Protean Design which specialises in cast bronze propellers- they make all the difference too! Often creating 25% more thrust than a standard brass item.
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Nick B

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Martin [Admin]

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Re: Twin prop direction
« Reply #5 on: June 06, 2018, 10:19:19 PM »


Yes a s Nick says, very much alive and kicking!

Simon here at last weekend's CADMA show...














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tugboyben

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Re: Twin prop direction
« Reply #6 on: June 06, 2018, 10:21:29 PM »

This May help
Contact details


Jason
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Martin [Admin]

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Re: Twin prop direction
« Reply #7 on: June 06, 2018, 10:58:57 PM »

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Brian60

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Re: Twin prop direction
« Reply #8 on: June 07, 2018, 07:38:29 AM »

On a tug viewed from astern there is some conjecture as to which way they turn is best. If they turn outwards, that is the port side turn anti-clockwise and starboard turn clockwise, the vortices or propwash lifts the stern upwards - it wants to ride on top of the propwash. If they turn inwards the stern wants to squat down - it is being sucked lower by the propwash.


The debate is which is best for towing, squatting down means it sets the props firmly in the water giving greater pulling power, but at the expense of possibly pulling the stern below water - this can be seen on a few youtube videos of anchor handler operations. If it rides the propwash all of the horsepower available will not be given to pulling the towed item.


Of course all this conjecture is largely irrelevant in the modelling world. All you need to remember is port and starboard props need to contra rotate with respect to each other.

rhavrane

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Re: Twin prop direction
« Reply #9 on: June 23, 2018, 09:07:29 PM »

Bonjour,
Thanks to this forum, I was able to reconnect with Simon that I knew from Propshop time. Here are my first acquisitions :
https://www.youtube.com/watch?v=nGRDus7uIJQ
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RaphaŽl
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Martin [Admin]

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Re: Twin prop direction
« Reply #10 on: June 23, 2018, 09:17:38 PM »



   :-))  Love your videos  RaphaŽl   ...... English subtitles PLEASE!   :embarrassed:

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rhavrane

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Re: Twin prop direction
« Reply #11 on: June 24, 2018, 06:55:33 AM »

Bonjour Mrtin,
I know that if I were able to share my videos with English-speaker steam and model RC passionates I would have more followers, but I have not yet found a moment to learn how to integrate e subtitle in a YouTube video. I thought the translation was automatic by clicking on a dedicated button... Promises, I will try to add English words for my video, my English needs to enriched with technical terms, not obvious to speak with Google Traduction on the pond  ok2
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RaphaŽl
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Shipmate60

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Re: Twin prop direction
« Reply #12 on: June 24, 2018, 10:17:32 AM »

With twin props it depends on the rudder(s).
If a single rudder inboard for manouverability, outboard for speed.
Twin rudders it doesn't make much difference.


Bob
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Perkasaman2

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Re: Twin prop direction
« Reply #13 on: June 24, 2018, 05:57:33 PM »

Outwards turning props for best manoeuvring at low speed and inwards turning props best for speed performance. Outwards turning props each have a sideways thrust component perpendicular to the shaft axis which is useful especially alongside when in port. This assumes tank steering/independant speed controllers for each shaft on twin prop installations.
I have always accepted the above as applicable in most situations irregardless of hull type. Both configurations give neutral handling in the straight ahead direction.
Twin rudders on the same axis alignment of the individual props will deflect propwash and vector or deflect their thrust.
These are the rules of thumb I have used.
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Fastfaz

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Re: Twin prop direction
« Reply #14 on: June 24, 2018, 08:30:36 PM »

Perkasaman 2,
      From experience when towing (scale type that is) outward turning props do not work as well as inward turning props. Read the post about stern lift its spot on.
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Bob K

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Re: Twin prop direction
« Reply #15 on: June 24, 2018, 10:18:33 PM »

Whatever may prove best for tugs and towing may not apply to hulls of slimmer and longer proportions.

On warships I have generally found that with multi props they seem to give best effect when the tops of the blades turn inwards.  Perhaps by driving water flow along the hull profile it causes more efficient flow over the central rudder to aid turning.  On a long thin ship the stern is unlikely to be pushed either up or down to any real effect, and towing is not a likely scenario.

Turing inwards seems to work best for me, but I don't have any tugs.

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TailUK

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Re: Twin prop direction
« Reply #16 on: June 25, 2018, 10:32:38 AM »

Let's keep a grip on the terminology, guys.  Two props on two shafts, turning in opposite directions is "Counter Rotation"  "Contra Rotation" is two props turning in opposite directions on the same shaft. (like the props on a torpedo).
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dodes

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Re: Twin prop direction
« Reply #17 on: June 25, 2018, 11:42:36 AM »

Depends if you wish to follow real life tugs or modelling theory. Standard twin screw tug with no kort nozzles, twin or single rudder are always outward turning for manoeuvrability, with a kort nozzle I would not expect much paddle wheel effect. British warships with CP propeller's have inwards turning props for fuel efficiency, Ferries with cp gear have outwards props for extra manoeuvrability. Though as my mate Bob says and I have some sense in practice, that a single rudder with twin shafts and one speed controller the model does steer better with inwards  turning props, as the spiral wash does veer towards the rudder. As a standard prop when turning gives two forces 1. forwards & reverse  2. Paddle wheel effect, it is a small force sideways in the direction of its rotation. That is why a single prop boat always carries about 3 degrees of wheel to counter act.   
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McGherkin

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Re: Twin prop direction
« Reply #18 on: June 25, 2018, 04:58:16 PM »

I think the only theory that really works when it comes to prop direction is fairly simple - Try both because it varies from boat to boat!
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