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[sunnybob]

Bluebird... a man after my own heart.

KISS has always been my favoutire acronym (Keep It Simple, Stupid).
With the boat on its stand, the prop tip is about a quarter inch BELOW the bottom of the rudder. With the prop blade turned to the top, it is on a level with the rudder top.

So, if I read this correctly, the rudder needs to go downwards a half inch, and upwards a quarter inch.

Yes?
Is there a similar rule of thumb to determine the width (depth?) of the rudder? the pivot is not central, measuring the whole rudder front to back, the pivot is at the 3/4 mark, with a quarter to the prop side, and 3/4 to the rear of the boat.

I can make new blades for the rudders quite easily, as they are bronze sheet, soldered into bronze pivots.

Ta, 

[John W E]

So, if I read this correctly, the rudder needs to go downwards a half inch, and upwards a quarter inch.

Yes?   yes - IF YOU have a look at the scribble that I have attached this would be the ideal rudder.  Where Gap 'A' on the drawing is close to the tip of the propeller, but, not close enough that it fouls the propeller.

and   'B' the overall length of the rudder is slightly larger than the diameter of the propeller only by say 1/8 of an inch.

- - - - - -

Is there a similar rule of thumb to determine the width (depth?) of the rudder? the pivot is not central, measuring the whole rudder front to back, the pivot is at the 3/4 mark, with a quarter to the prop side, and 3/4 to the rear of the boat.     To say there is a rule of thumb, there is and there is not - there are many different types of rudder as you will already know and also many shapes too.  So, rather than going down another 'hair raising path' and becoming confused - we will stick with the path we know and try these methods first.

I can make new blades for the rudders quite easily, as they are bronze sheet, soldered into bronze pivots.    My advice to you will be it is easier to stick on pieces of Plasticard for a trial - this will give you an idea of the size you require for your rudders and the performance you will get from them - then, when you are happy with that you could possibly manufacture new rudder blades from bronze or brass.

Aye
John e
Bluebird

[DickyD]

If you didn't spend all day sleeping John you could have saved us all a lot of hassle.   

[sunnybob]

from that drawing, these rudders are never going to work well.

Strange, I have the original plans for this boat now, and they are built to the plan in almost every way.

But what you say makes sense, so i may well end up altering them just because I can! ::) ::)

This is the best pic i can get tonight of the rudders,

[grasshopper]

Are the plans of a real (as in 1:1 scale) vessel - because although you may have replicated the real ship and it's hardware exactly to scale, it will handle differently because you haven't got scale water - or am I just being stupid?

[John W E]

hello there Sunnybob

This is for information and interest only; the plans look familiar or should I say the model looks familiar - are they from the Vic Smeed category of drawings? Just out of curiosity.

If the model is based on a 'real' vessel there has been some, shall we say, builders' licence used regarding the angles of the propeller shafts & the distance from the hull.

The angle of a propeller shaft does alter the characteristics of any boat's performance and I notice you have a fair gap between the tip of your propeller blade & the bottom of the hull.  Now, on a real boat/ship the distance between the top tip of the blade and the bottom of hull normally eqates to 5% of the diameter of the propeller.  This has been found to be the optimum gap.

One of the reasons which come to my mind for the angles of your propeller shafts being so steep is, it does look to be a fairly 'old' hull/plan design - dating back to somewhere to the 1960s.   If we think back to then - electric motors were of a rather large size, thinking of Taycol and soforth. With such large motors, you could not get the propeller shaft close to the hull without some form of gearings.

There may have been the possibility that the model was originally built with no radio control in it.  In its original life it may have had a ratchet system on the rudder, this was for setting the rudder at a set position, and then one would let the boat away and sail under its own course - hopefully to return to the owner.  Just food for thought.

aye
john e
bluebird

[malcolmfrary]

Actually I think you will find changing a single prop from clockwise to anti clockwise aint going to make a jot of difference Malcolm. Undecided

Rudder. I meant RUDDER.  Silver moment.  I wil go and stand lean in the corner.

[farrow]

With a standard screw arrangement, real vessels have a maximum movement of rudder set to 35 degrees any more rudder has no extra effect and can brake the vessel movement through the water to an extant which slows her turn and damages the rudder assembly. Design of rudder and vessels trim play a greater role in turning than putting on more degrees. There are some special designed rudders that will go alot further but they are for turning at slow speed and too complicated to talk about here.

[sunnybob]

Bluebird, youre very close on a couple of points.
With the invaluable assistance of Colin Bishop on here, I have found the history of this boat, which I helped my dad make in the late fifties.

iT IS based on a real boat. the "Gwen Eagle". The boat was built in 1949, and the drawings were on sale in 1951.
This boat WAS designed for R/C, and I remember the huge heavy parts on the shelf in my dad's workshop.

The hull was completed around 1960 but sadly never fitted out. I have just completed the project almost 40 years on, and it sailed under its own steam (so to speak) for the very first time only 2 weeks ago, hence this discussion now.

As the boat has huge sentimental value, due to my dad hand building the props and rudders, as well as the hull, I'm not going to fart around with them. If I need tighter steering, I shall just have to perfect my 3 point turns.

Thanks for all the info, I have learnt a lot here.
Bob
 

[Shipmate60]

Sunnybob.
There is no need at all to change the rudder/prop set up, but it will cost more than a fiver.
Either use seperate speed controllers on individual channels on your transmitter.
OR
Fit the new ACTion P94 mixer/twin speed controller unit.
You can see in my video of Prinz Eugen Finally Gets Her Bottom Wet.
This unit will turn a 10 foot cruiser hull in its own length.
The beauty of this unit is its size and you can transpose to other models, so can work out cheaper in the long run.
This would give you a very manouverable model without modifying any of your dads work.

Bob

[John W E]

Hi there Sunnybob

I think you have got it spot-on when you say leave well alone. Even if the steerage is not that good; sometimes when we try and improve things with adding bits and pieces and new electronic Gizmos it does tend to spoil a model.

In an ideal world, and, of course if money were no object - it would be nice for you to try a 1960s style radio control - to go with the model.   Obviously, the radio would not be half as good as today's radios - but, It would be well within the character of the model.   Also, it would have been just as your dad wanted it finished.  To do the model as you have done is, in my eyes, a nice tribute to your dad.

aye
john e
bluebird

[Colin Bishop]

I agree with Bluebird. It's a vintage model design, probably not intended to turn on a sixpence but to make its way across the pond in a stately and sedate manner, just like the prototype. Enjoy the vibes!

Your Dad would have been very pleased to know that you have completed his project and that she is afloat and moving under her own power at last.

Colin

[BarryM]

Just to throw something else into the pot, it isn't the rudder itself that turns the boat, it is the hydrodynamic imbalance it imparts to the hull - a sort of leverage effect. As TT says, once you go beyond a certain angle of throw, and 35 degrees sounds about right to me, the rudder justs acts as a brake.

Colin, Unless all I was taught in those Naval Architecture classes is wrong, the rudder most certainly does steer the ship by creating forces on the hull which cause it to pivot around its longitudinal center of rotation. A rudder works in exactly the same way as an aircraft wing. When it is central, the water passes over both sides and no thrust is created in either direction. When the rudder is put to port or starboard, a  low pressure area is created on one side acting at the center of pressure and the rudder naturally moves bodily in that direction, pushing the stern in the desired direction. The steering force will increase with the rudder's angle of incidence until at a point between 35 deg and 45 deg (depending on design) it will stall just like an airplane's wing when the nose is pointed too high for the prop thrust. Thus most rudders are limited to 35 deg. It's not a question of drag, just that a stalled aerofoil will not steer - how does a pilot regain control of a stalled aircraft?

There are 'high-lift' rudders which utilise greater angles (I am struggling to remember the name of  one which was very effective in full size use which had an unusually thick aerofoil). There are also the flap rudders such as Flettner and Becker which use trailing flaps to increase the steering effect while reducing the load on the main rudder. Even more exotic are rudders with inbuilt thrusters permitting the rudder to act without requiring the main propulsion to provide water flow over its surface.

In our model world I doubt if different aerofoil shapes or flaps have discernible effect (shoot me down somebody) and it all comes down to blade area, position and water speed over the blade.  

[Colin Bishop]

Barry, that's more or less what I meant, I'm not technically qualified so didn't express it very well - Bluebird explained it much better in Reply 14. Moving the rudder alters the hydrodynamic forces acting on the hull causing the ship to turn. On a model I think it's probably true that too great an angle results in drag in practice if not in theory. If the rudder is close to the prop then the water will tend to be thrown out to one side which will bodily push the stern the other way. Full size yachts make use of this effect to move the stern around when maneuvering in marinas and I use it to waggle my single screw scale boats around on steering courses.

[sunnybob]

Thanks for the kind words, folks, I hope my dad would have liked what we've done with his boat.
The internals were just rotted, and all had to be dumped, so I dont feel bad about fitting the latest motors and control gear.
But the outside is all his own work, so that is not going to be mucked about with.

I have the whole "family launch" thing next sunday, with my mum performing the renaimg ceremony, so I'll report back on how the boat performed.

Thanks to all for advice and help.

Sunybob