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[Mark66]

Hi all does anyone know which way a larger center prop should rotate on a triple prop set up, do I get a left hand or a right hand prop, my two outer props are running from the rear as follows.




Left hand clockwise.
Right hand anticlockwise.




It's also a triple rudder if that make's a difference.




Thanks all.


 

[rnli12]

Mark,

I have run several 3 prop set ups and provided the prop sizes are all the same it should make little difference. So two props will turn one way one the other.

But I did notice better handling if looking from the stern the props turn outwards when in ahead, other modellers will have there own thoughts I am sure. PT Boat & eboat.

Either two left handed turning anti-clockwise and right handed clockwise or vice versa, like I said I felt the cavitation was better displaced on mine and trim was better.

On one occasion I increased the centre prop size to see if it ran any better. no change!

Regards,

Rich

[RAAArtyGunner]

Good question?

Seem to recall seeing pics of a three prop "fast" boat with all props the same size and turning in the same direction?

[Jerry C]

As you have three rudders, when looking from astern and turning ahead, port prop anti-clockwise, Center either way and starboard clockwise. When manoeuvreing use only wing engines when doing full speed use all three.
Jerry.

[Mark66]

Thanks all.




So I could use the configurations mentioned to see which the boat suits best.


In order for the outer wing engines to help manoeuvreing would I need the Action electronics mixing unit ???




Thanks you for your reply's. 

[craggle]

Titanic had one clockwise and two anti-clock by the looks of it.
Not sure why though, must have been a reason?


Craig.

[raflaunches]

In my RAF Marine Craft Directorys in mentions that the twin and triple engined and propped launches all turned in the same direction as it was easier to have a common engine and gearboxes that were interchangeable whilst larger ships like Titanic had to have specially made items that had to stay in the ship.


I think it was only the 1950s that the RAF eventually changed to two different gearboxes allowing opposing turning propellers.

[jaymac]

My weisel runs 3 in the same direction and has 3 rudders no problem  doubt you need a mixer what type of boat is it?

[craggle]

I seem to recall the centre prop in the Titanic was driven by a steam turbine and the outer engines were the reciprocating piston engines.
Not sure if that made any difference to the props?

Interesting subject

Craig.

[dougal99]

Thanks all.




So I could use the configurations mentioned to see which the boat suits best.


In order for the outer wing engines to help manoeuvreing would I need the Action electronics mixing unit ???




Thanks you for your reply's.

If you are running both motors from one ESC and you want them to run at different speeds when turning then yes you will need a mixer unit.

[Colin Bishop]

I don't think it has been mentioned but if you have two props running one way and the other in the opposite direction and they are screwed onto their shaft then it makes sense to have the middle prop rotating clockwise as seen from astern as that will tend to tighten it when the model is going forwards.

Colin

[Buccaneer]

Colin, are you sure? I have spent 10 minutes on this with hands going in all directions. If the prop is going clockwise then so is the shaft. If the prop suddenly stops but the shaft continues to rotate it will screw itself away from the prop. If you look at the shaft from the other direction, i.e. forward looking aft, it is like undoing a bolt out of a nut.

Open to comments!!
John

[Colin Bishop]

You know John, you could be right there if the prop is caught but if it is simply rotating normally it will tend to screw itself tighter. I suppose it is a question of which is the bigger risk!

Colin

[Buccaneer]

Sorry Colin but I can't buy that one. All the tightening or loosening force is provided by the shaft and the resistance by the prop. There is no force on the prop to keep it tight or make it want to screw on.

John

[Colin Bishop]

Not 100% convinced at the moment. Turning the prop will result in the thrust tending to wind it onto the shaft I would think but I admit I could be mistaken.

Colin

[RAAArtyGunner]

Think you are both right 

The shaft gives inertia to the prop.  (makes it rotate).

So in theory when the shaft stops suddenly then the prop "continues" to spin until it runs up on the shaft thread and then comes to a stop.

Explains the comments from those who have lost a prop when reversing and the advice to use a lock nut against the prop.

[derekwarner]

This is a complex box of possibilities  ....[all looking on the propeller from the stern]

1. if we consider the Stdb clockwise propeller as tightened up against a propeller shaft shoulder [with a left hand thread] it is the same as torqueing a nut to a bolt
2. the clockwise rotation of the propeller shaft against the set of the propeller maintains the mechanical integrity from the initial torque applied, as the forces on the propeller blades aid to maintain the applied torque
3. if we consider the Port anticlockwise propeller  as tightened up against a propeller shaft shoulder [with a right  hand thread] it is the same as torqueing a nut to a bolt
4. the anticlockwise rotation of the propeller shaft against the set of the propeller maintains the mechanical integrity from the initial torque applied, as the forces on the propeller blades aid to maintain the applied torque

I understand there were always exceptions to the preferred design criteria

Scale models built with standard taper shaft and taper reamed propeller bores, and retained by an external threaded nut 5/8 times the diameter of the actual shaft 

Controlled heating a bronze model propeller [with a taper reamed bore] to ~~ 150 degrees C, then sliding this onto the tapered stainless shaft and contained by the threaded nut will result with an installed joint that will never fail

Modern high speed craft are a different kettle of fish all together

I understand multi shaft vessels such as the Titanic were installed with tapered shaft mountings for her propellers

Derek

[Mark66]

My weisel runs 3 in the same direction and has 3 rudders no problem  doubt you need a mixer what type of boat is it?

Hi, it's the Adolph Bermpohl it's a bit of a resurrection job but i'm enjoying it, running on 40MHz it's 35 years old but I like the vintage boats.

I have read all the comments I must admit I never thought about losing props.

[rnli12]

Hi,
 
All the technical comments are very good but looking back at the original question I have never had an isues with my props in 1, 2, 3 & 4 prop set ups in any direction of rotation!
 
Rich
 
 

[Mark66]

Hi,
 
All the technical comments are very good but looking back at the original question I have never had an isues with my props in 1, 2, 3 & 4 prop set ups in any direction of rotation!
 
Rich

Hi,


It's the first triple prop I've had so I want to be sure everything was rotating as it should, most of the connections I found to be reversed from the motor wires to the transmitter. I just wanted to make sure the running gear was as it should be for a triple prop, just switching props L/R R/L over can cause problems even with the motors running in the right direction.