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[Barney Magrew]

I have a twin screwed boat which has a single rudder.  The boat goes fine in a straight line and will turn on a sixpence (per decimal!!!) with one ahead and one astern.  However, when going forward and into a turn, the boat turns OK to the left but won't turn right at all.  I have changed the direction of the props, no difference.Any ideas please?

[captain_reg]

Do both the props rotate in the same direction? I've always run twin props with each rotating in a different direction and never had any issues. Looking back at some photos it seems I have the bottom of the props turning in towards each other. I know there is some debate as to which is the correct way but I can never remember. I've always had one rudder per prop so this may not apply to you.


You always have the option of electrickery to slow & speed up the correct shafts to get good turning. Some transmitters can do it I believe or Action electronics sell a box.

[jaymac]

Obviously  you have checked what is happening Out of the water is the rudder perhaps  only moving properly in 
one direction the  turning ok using tank steering the rudder irrelevant but whatever you are using to achieve that may have some bearing a wrong connection can cause problems. I  vaguely recall  a problem with an action device the rudder control  did the magic on the motors either slowing and or reversing one for  manoeuvring almost sunk the fleet. This was a large tug built my a late great builder on here if you describe your setup should help

[Akira]

A few ideas to consider:Test the rudder function out of water. Does it move to the same extent in both directions? Is the grub scrw tight on the rudder shaft? Did you file or machine a flat on the rudder shaft for the grub screw to seat upon? Were your transmitter controls in neutral when you set up the rudder mechanical conections? Does your transmitter allow you to adjust the throw of a control in it's programming, and if so, is it set equal for both directions? Does your rudder swing freely in both directions and to the same degree when disconnected from the servo? Are there any electronic devices included in the steering circuit of the radio receiver/servo connection that might effect the rudder's response?I hope you find a simple answer.

[Capt Podge]

It sounds like the rudder isn't catching the wash from the starboard propeller, so... Is the rudder absolutely central to the props?
Are you getting the same rudder throw (angle) to Port and Stbd?
Is the tiller on a closed loop (2 rods of equal length) and utilising the same hole on both sides of the tiller arms?


Here's hoping it's something simple...


Ray.

Oops, sorry, didn't see Akira's post at the time of posting this response.

[Barney Magrew]

1.The props turn inwards at the bottom.2. The rudder is dead central and turns equally in both directions.3. The props appear to turn at the same speed.4. Everything is tight and loctited in place. 5.  Other than the ESCs and the rudder servo there are no other electronics fitted.

[Capt Podge]

Hmm, I'm pretty much stumped now.
What type of esc are you using?


Ray.

[Barney Magrew]

Quicrun1060, but I can't see what difference that would make as both props appear to be turning at the same speed.

[Capt Podge]

Ah ok, I've no experience with those anyway.


Sorry, can't come up with anything further.


Ray.

[tonyH]

What sort of boat is it: Slow and steady displacement hull or fast and furious powerboat? Does she lie flat side-to-side and is the rudder perfectly vertical to the waterline and heel into a turn to the same extent both ways? If she leans more one way than the other it can certainly be that or even the ballasting that affects the steering as I found recently with this. 

[Barney Magrew]

It's a tug about 30ins. long.  Sits perfectly upright in the water and doesn't heel, to any great amount) when turning.

[tonyH]

Sorry Barney, events overtook me but I added the bit about the rudder. A bit irrelevant in your case

[John W E]

hi there


When you set the model off on the lake in a straight line; both transmitter throttle sticks set the same; does your boat tend to wander off on one side?

Just out of interest - propellers only thrust on one side, when going forward & in reverse.   So, if you put your model in the bath and put your hand gently behind each propeller MAKE SURE YOU DONT GET YOUR FINGERS CAUGHT IN THE BLADES - IT HURTS - you will find which side of the prop the thrust is on.

If it is the outer segments (in other words close to the outsides of the model) your single rudder will not be in any thrust wash of the propellers onto the rudder.

The best/easiest way if you don't have a rev counter; to check you are getting the same input to each speed controller & therefore the same input to each of the motors/propeller shaft - is to replace the speed controllers with 2 standard servos (one for each channel) and move your throttle sticks up to full forward and full reverse to ensure that you are getting full movement on both servos.   If you are, you know you are getting the same on your speed controllers.   I have had a transmitter which the left channel and the right channel give slightly different throwns on the servo.

Have you got one of these fancy speed controllers which are a one button press set up?   Because some speed controllers only work in 50% astern and you may just have one of them set up wrongly.   Easy remedied, if it is this, just swap the wires around on your motor.

Last but not least ensure that both propeller shafts turn freely.

Going back to the thrust on the propellers though, if it is thrusting on the outside try different handed props - so that it now thrusts on the inner side of the prop blades.


Hope this helps.


John

[tonyH]

Do the props actually match? You wouldn't notice going straight forward/reverse because you've probably trimmed the rudder on the tranny. Nor are you likely to notice it if you're "spinning" on the ESC's or with a mixer. You'd only probably notice it when you do a normal turn because one prop is more efficient than the other.Are both sides of the hull exactly the same hydrodynamically, even down to the smoothness of the paintwork! That would also be adjusted out when you trim on the tranny.
Probably a load of Dingos'..........but it's fun speculating about forces and resistances in the hydrodynamic equations

[Barney Magrew]

The rudder has been removed from the boat and surprisingly all is well, especially with tank steering.   Very, very manoueverable.  May play with the size of the rudder, both in length, and in height.  Who knows.Thanks to those who took the trouble to post.

[Capt Podge]

Glad to hear you've got the problem resolved - let us know how you get on with trials with any reworked rudder, should you decide on changes please - it'll be of interest anyway.


Ray.

[Akira]

Tank steering works wonderfully. That said, I'm still stumped by your issue. I have three, twin screw, single rudder boats, two destroyers and an icebreaker, all 1/48th scale. While none of them turn on a dime, the full scale version did not either, all respond well and equally to rudder commands in either direction.I have read that while your prop rotation set-up is prototypical, reversing the prop rotation direction can sometimes make a difference.Lastly, a rudder extension, not even a big one, can make a huge difference.

[jaymac]

How are you managing tank steering don't see how that esc can operate the motors independently

[NickelBelter]

How are you managing tank steering don't see how that esc can operate the motors independently

I think he has two, he used the plural form earlier. 

It's a perplexing problem, but all signs point to a rudder malfunction, either physical or electronic.  If it goes straight with the rudder admidships and turns to port on rudder alone when commanded, that would indicate the rudder is properly centered and has enough hydrodynamic force to turn the hull.  If the props are counter-rotating (whichever way, tops turning inwards or outwards) and the model goes straight that would indicate that both motors are turning at the same speed and the counter-rotation is cancelling out propwalk.  Thus, the only way it could not turn right on rudder alone would be if the rudder was physically not moving to the right. 

[jaymac]

OK  but with tank steering why use the rudder and if you want to bit awkward without another hand  even then
 the Rx might  not like sending out 3 signals at the same time. Barry have you tried  reversing the  motor signal  from the Rx   see if it then only turns right. Also are the Rx's powered via Bec or its own Battery