Model Boat Mayhem
Mess Deck: General Section => Model Boating => Topic started by: sunnybob on May 14, 2008, 08:44:13 pm
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Ok, I'm back! The boat has performed well in its sea trials in all but one respect.
Theres not a lot of steering going on!
I have a standard servo, with 45 degrees either side of dead ahead, but I want some more degrees on both sides.
I recall hearing about a gadget that increased servo arc, can anyone point (steer :D) me to it please?
Thanks, O0
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Either extend the length of the servo arm or reduce the length of the rudder arm, both have the same effect.
Bob
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Now, I had just about come to that conclusion, but the servo is connected to the rudder by two brass rods in a "push me pull you" way.
if i increase the length of one arm wont that over stress the rods? If the front arm is traveling further, wont the rods bend?
My brain hurts now :embarrassed: :embarrassed:
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You set it up on the outer holes on the servo arm and closer ones on rudder arm, did you use adjustable links?
Bob
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No, I dont have adjustable links. just 2 straight brass wire rods.
I've just been playing, and think i might get what I want by just making a couple of wider arms, one each for servo and rudder. If I keep them the same length, but further apart, then there will be more travel on the outer edges, wont there?.
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Is this the Canal Boat?
Have you any pics of rudder linkage and rudder/prop.
Bob
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no, its a cabin cruiser.
I think I can achieve desired results with wider bars on servo and rudder.
Attached is the best pic I have of the steering, taken a while ago during mock-up stage.
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sunnybob,
If you use a standard 4 arm servo horn it will be longer than the small one you have fitted.
Just set it up and cut off the 3 unused arms.
Bob
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Hi,
I think if you increase the length of both servo and rudder arms, keeping them the same length as each other, you will only get the same rudder throw as before.The angle the servo turns through is what dictates the rudder throw.
However, if you have a larger radious on the servo arm than on the rudder arm, the rotation of the rudder will be increased relative to the servo. This is because the tip of the servo arm travels further to turn (say) 45deg than the rudder arm tip will to turn for the same number of degrees.
Think of it in terms of the circumference of a circle, a 1" circle has a greater circumference than a 1/2" circle but has 360 degrees, just the same as any circle.
Clear? I hope so!
Ian
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I think I can achieve desired results with wider bars on servo and rudder.
At the risk of making myself unpopular, IMHO the only reason for those push-me-pull-you arrangements is psychological. They are necessary when you have stranded wire cables as connections (so-called "closed loop", such as that system often fitted to RC sailplane rudders) but for stiff, straight pushrods the purpose just eludes me. That's my first point...........
Next, if you think about it, lengthening both the servo and tiller arms by an equal amount will do nothing to increase either the movement or the torque. They both rotate by the same number of degrees now, and they'll do exactly the same even if you double both lengths. Draw a scale picture and work it through (I can feel Bluebird reaching for his pencil as I type!).
The only way you'll increase the throw is by doing as Bob suggests i.e. further out on the servo arm and/or closer in on the tiller arm.
While you're at it, I'd advise you to move the servo back to the next frame aft as close to the rudder as you can get it. Those rods are unnecessarily long and wappy, and need to be as short as possible. Finally, connect one rod from the servo to the tiller. Use model aircraft ball-and-socket adjustable clevises and piano wire of 14 SWG with a threaded adaptor soldered onto each end. If your model shop doesn't stock these then stop going there!
Works for me, but suit yourself.
FLJ
Just seen Ian's post. Nice to think I'm not alone on this one! ;)
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I was thinking exactly the same as FLJ
You only need one push rod, as it is solid. This allows you to move the position of the rod on the servo arm (outwards) and/or tiller arm (inwards), to get the throw you want.
I also seem to remeber that there is another post somewher on here. It says something like 'at speed a rudder angle of more than about 35 degrees is counter productive due to turbuelnce'.
So it might be worth asking - what type of boat is it? how fast is it? do you have probalems at low speed?
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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.
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Looking at the photo again, that is one big model. It may be that the rudder just isn't big enough.
The turning moment will be a function of the area of the rudder and the angle of deflection. When I made those noisy things that go up into the air I always designed control surfaces with as large an area as looked reasonable and then kept the movements relatively small. Has the same effect on turning as a smaller rudder deflecting more, but much easier on the drag (or turbulence, in this case).
As a very rough estimate I reckon you need between five and six square inches of rudder (balanced) on a beast that size, and 35 degrees each way sounds about right as a maximum.
FLJ
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You need a set up as FLJ and TT suggest with one rod from the servo to the tiller using model aircraft ball-and-socket adjustable clevises and piano wire of 14 SWG with a threaded adaptor soldered onto each end.
Or you could use M2 steel rod with adjustable klick links or adjustable ball couplings.
These are all available from http://www.cornwallmodelboats.co.uk/acatalog/installation_accessories.html
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Hi one and all
Ah, I see me name has been mentioned....the reason I use a closed loop system for the steering, in the beginning our movement originally comes from the single point of rotation from a Servo. Going to the laws of physics for every action there is a re-action, and, in the laws of engineering, with a movement of action you also have resistance to overcome, which creates wear.
In our Servo, we are converting a rotating movement into a back and forth movement and then back into a rotating movement – via a system of cranks. Also in this setup of movement we have a system of leverages. This also applies strain or friction on our single-point of movement.
To reduce wear/strain on our Servo motor, should we not balance the load equally either side of the pivot point? You have the same force pushing and an equal force pulling. The forces around the centre point you will find to be equal. In other words less strain on the servo motor for a given load. Think of riding a ‘push bike’ is it easier to turn the handlebars with one hand and arm or is it easier to turn it with two and balance the load of the front wheel – and before anyone clever says you lean a bike over to turn the corner, we are talking theoretically here.
Here then also are some thoughts which date back to when I designed and built my real boats and I had to overcome calculating sizes and positions of rudders. The rudders when moved one way or the other out of the centre line, have the effect of first of all moving the stern (assuming they are located aft) Athwartships, thereby momentarily causing the fore and aft line of the boat to assume an angle to the path along which the boat is travelling as a consequence the water ahead of the boat, as it is reached, the hull will find a lateral surface presented to it considerably greater and of different form to the usual frontal surface presented in straight running.
It is the action of this water on the hull surface presented that causes the boat to turn. It will be seen, therefore, that in order for the boat to turn rapidly and steadily the area of effective lateral surface presented to the oncoming water must be larger in front of the pivoting point than aft of it. This pivoting point is also dependent to some extent upon the hull form and trim.
In some cases a hull needs the addition of a little additional keel area forward to help turning. A small plate or fin can produce the same effect.
Given good design, therefore, of the hull from a point of view of its lateral resistance to turning and, a good balance of areas before and aft the pivoting point; there should be no need to have rudders particularly large.
Such area as is provided for rudders is, however, much more efficiently employed when placed under the hull as opposed to being hung on the transom. In the latter case the water flowing pas the rudder blade will tend to rise and spill over a deflected blade, thereby reducing the impact pressure tending to make the blade effective. If it is desired to employ an externally hung rudder, it is a good idea to have a plate formed over the rudder blade, which to some extent substitutes for the bottom.
To ensure maximum rudder effect from given blade area, the maximum effect of slipstream from the props should be made use of. This will involve placing the rudder blade near to the propeller and of such dimensions that nearly all of the disc area of the propeller impinges on the rudder.
It will be noticed very clearly, if, for instance, a large prop involving greater shaft angle has only a small portion of its disc area of slipstream impinging on the rudder. A considerable fall off in rudder effect results.
To assist in operating the rudder through the normal form of tiller gear, power-operated servo or similar systems are sometimes employed for the larger fast types of craft, but a substantial reduction of turning effort can be achieved by ‘balancing’ the rudder.
This involves locating a certain proportion of the area of the rudder in front of the vertical or stock axis which helps to balance the effort required to force the rudder blade into the path of the oncoming water and slipstream.
In practice there is a limit to this amount, as although quite a large degree of balance can be used to help in the initial angles, after a certain point ‘reversal’ can and does take place, which has the effect of helping the rudder too much too hard over, the oncoming water then holding it thereby a considerable force.
About 22/23 percent of balance is the maximum which has been found to be safe to use.
The shape of a section of a rudder suitable for high speed craft is a subject which has been debated rather widely by the various authorities concerned. There are at least two considerations which have to be taken into account here.
There is the case where the rudder is amidships when the optimum shape will be that which offers least resistance to forward motion. Here the situation could be expected to be similar to that described in the case of the strut, where optimum section beyond a certain speed will probably envisage maximum chord about midway between leading and training edge. Entry and exit should be sharp.
The other consideration refers to the qualities possessed by the rudder from the point of view of turning. Here the situation is somewhat different, in that the flow of water will impinge on the leading edge of the rudder at an angle. For maximum effect here a rather blunt rounded section will probably prove most effective.
Equally, when considering the efficiency of the rudder section from the point of view of turning, it will be found that it is undesirable to reduce the trailing edge to a point; some reasonable width here greatly assists the effectiveness of the rudder.
Aye
John e
Bluebird
I wonder should I have posted this on Nautical strange but true ::)
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Pure poetry John, absolutely wonderful, a stroke of genius, so much effort, put your heart and soul into it. (http://i124.photobucket.com/albums/p8/DickyD_photos/crying2.gif)
So we need two rods and you're not sure about the size of the rudder(http://i124.photobucket.com/albums/p8/DickyD_photos/thinking1.gif)
(http://i124.photobucket.com/albums/p8/DickyD_photos/tumb.gif)
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Hi there
To calculate the size of rudders required; we need several pieces of information first i.e. the total 'wetted' surface area of the hull; at a given speed. The average shape of the hull in a block co-efficient, Also, shaft angles of the propeller shafts, the size of propellers and the blade areas - along with RPM at the desired running speed and shaft horse power. This will help us to calculate the centre of turning reistance on the hull.
A quicker way Dicky is to go to ACTion Electronics and purchase a motor rudder mixer {-)
aye
john
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Good god I've started him off again. :-\ >>:-(
Haven't you got a ship to build John ?
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I am with Bluebird on this one.
With a single operating arm it is possible when going astern that the force of the water forces the rudder too far one way and it ends up jammed as the pivot has gone over centre.
Where possible I always use 2 actuators then this cannot happen.
Does this happen often, not really, but when it does the rudder is jammed one way.
This happened on SteamBoatPhil's springer at Beale. So it can happen to even the most experienced modellers.
Bob
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Just checked the pic again.
Can you confirm she is single screw twin rudder?
Bob
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Judging from the width of the beam and the position of the shaft i would say she is Twin screw with what looks like the ESC between both shafts.
I maybe wrong but thats what it looks like as the shaft looks too far over for a single screw.
Need a overhead pic of the whole set-up me thinks O0 ;D
Jay
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It is not always the case that we need two arms, and in some cases it may not be a good idea.
For example when you want to increase the throw of an arm.
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Just for the benefit of anyone reading who is unfamiliar with the term 'balanced rudder' I have attached a diagram.
It is something that had to be explained to me.
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You are right she is twin screw twin rudder.
A pic of the props rudders would be of great help if possible.
Bob
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I
Where possible I always use 2 actuators then this cannot happen.
Does this happen often, not really, but when it does the rudder is jammed one way.
This happened on SteamBoatPhil's springer at Beale. So it can happen to even the most experienced modellers.
Bob
Not really a good example Bob, isn't SteamBoatPhil into straight running ::)
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hi there all
A quick and easy method which I have used in the past to equal out the length of the steering push rods is to use the ever useful terminal block insert. Basically, one of the pushrods has been made up from 2 lengths which are joined in the middle with the adapting block, to allow adjustment of length of that pushrod.
When we are happy that the pushrods are of equal length, I either, put a drop of solder over the pushrods and brass insert or, some epoxy.
I have attached a sketch/scribble to explain me meaning:
With hindsight, and going back to the original question and also looking at the model - this model may be built with scale rudders - these in past experience do not give the best turning circles on models for some unknown reason. So, by increasing the rudder size slightly; rather than trying to tamper with the throw of the rudder may be of a more successful approach.
Aye
John E
BLUEBIRD
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Scale rudders are never really effective. You cannot scale the density of water.
And while some things are affected by a power of 2 (area = squared/sqrt)
Others are effected by power of 3 (vol = cubed/cbrt)
There is a rule/law to explain this.
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I am with Bluebird on this one.
With a single operating arm it is possible when going astern that the force of the water forces the rudder too far one way and it ends up jammed as the pivot has gone over centre.
Not only possible, but I've seen it done on several occasions. The servos we use may have approximately 90 degrees of travel, but they do not have stops to prevent overtravel from external forces - going astern, collision with underwater obstacles, operator in blind panic mode etc. The closed loop system is an excellent failsafe highly recommended for a vessel which may be sailed on waters from which recovery maybe somewhat tricky.
-Rob
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With a servo going 45° each side, this is more than enough given a rudder that is big enough and in the right place.
Trying for a larger throw by having a longer servo arm / shorter tiller arm usually results in the tiller arm going over centre and locking up sideways, to the embarrassment of the owner.
A single pushrod, assuming it is rigid enough, does the job, unbalance strain being taken by the bearing on the servo output shaft. This is unlikely to wear out in any of our lifetimes, so should not be a problem.
Two pushrods works when both the servo and tiller arms are the same length - otherwise, either the rods bend, or the servo or rudder post are pulled out by the roots. If the pushrod to arm connection has any play, then the longer the arm, the smaller percentage the play.
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Blimey!!! That woke you lot up!! :D :D :D
Ok, I cant possibly answer all that individually, so heres a brief run down and (hopefully) a pic that will explain most things.
Boat is 40inches long, 12 inches across.
twin motors, single esc. ACT distribution board. twin screws. twin rudders. single servo for rudders.
I realised after posting that just extending the arms wouldnt work.
I only want a small improvement in steering. i cant fit bow thrusters, and do realise the limitations of a long ship steered from the rear. I dont want the extra expense of fitting another esc to allow one forwards and one backwards.
I have also found the hard way, that the servo arm to wheel system in the mock up pic is flawed.
The large / small gearing combo would seem to offer what I want, but suerely that would not work, as the distances between the connection points of the arms will change as the arms turn, causing either excessive drag, or sloppiness.
My main reason for starting this was I had heard of a kit that turned a 90 degree servo movement into something closer to 120.
As said before, my budget for this boat is totally expended. Any solution costing more than a fiver will NOT be taken up ::) ::)
I'm going to stick to the push me pull you, for the reasons already listed, and the angle of the boat stern stops me from locating the servo any closer, so I physically cannot shorten the linkage.
Thanks for the interest, keep it coming. O0
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A fiver, can beat that!!
Try adding plasticard each side of each rudder to extend the rudder length.
If possible both fore and aft.
If it is successful extend the rudder by soldering a brass plate to it and fairing in or just make a longer blade.
Bob
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That might work on the model shown Bob ,i tried it on a RTR southampton and it did "xxxxx" all .
The other cheap optoion for sunnybob might be to fit a couple of micro switches on the servo to kill power to either motors ,ie steering port then the port motor is off so the st/board motor has the thrust.50p for a pair of switches O0 .
daz
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Daz,
The rudders look a bit small and half the propwash is passing under the rudders.
Bob
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Your right Bob , they are a bit on the small size A bit of extra meat on them would help .
daz
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Right, I made a new rudder bar, and now heres a pic of the total turn on the rudders.
Excuse the poor quality, i had to lay on the floor with the camera and operate the t/x with the spare hand :o :o :D
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Sunnybob, Hi there
Last question, looking at your photographs - it is difficult to tell whether your propellers, when viewed from the back of the boat to the front, turn inboard or outboard - meaning your starboard or right propeller turns clockwise and your port/left hand propeller turns anti-clockwise.
In this rotation mode, they would move the boat forward. Now, if the propellers rotate in the opposite direction e.g. starboard one turning anti-clockwise and the port one turning clockwise to move forward - this may have some bearing on the steerage of the boat. Some vessels have a poor turning circle when the propellers turn inboard. But, having said that there are one or two vessels which having the propellers turning inboard improves the steering.
Now that has opened a nest of hornets :D :D
aye
John e
bluebird
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What I want to see is a picture of the model, the whole model, with the cabin on. It looks a real beauty.
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well, I had to go start it up to check that. Viewed from the rear, the starboard prop turns clockwise, and the port prop turns anti-clockwise.
Is that good? or bad? :D :o
I am much happier with the steering now i have made two equal length arms. I shall give it another bash around the lake as soon as it stops raining and report back, but I think it will do, for the limited amount of time this boat will actually be in the water.
attached this time is the boat on her maiden voyage, as requested (lol) The water is very muddy due to heavy rain in the stream the day before.
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VERY pretty model. The accepted wisdom is that with twin rudders it makes very little difference whether your twin props turn outwards (like yours) or inwards (which gives better steering with a single rudder). My preference is for outward turning on high speed models and inward on the slower longer ones which need as much help to steer as they can get, even with over-scale rudders.
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I get better turning on my minesweeper with inward turning props O0
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I cant change that can I? Even if I swap the props and reverse the motors, those props will always push the same way?
(I never could think in 3D)
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You've just said it swap the props and reverse the cables on the motors. Your props are handed. O0
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DickyD,
Rotation of props wont make a great difference if most or rudders are out of the propwash.
There isn't enough water being pushed against the rudders unless you increase the speed through the water considerably.
Inward turning props assist single or triple rudder.
Bob
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Bob I was just following on from cdsc123's posting and explaining to sunnybob how to change from outward to inward turning props.
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so can someone clarify this for me please.
Is it worth the effort of reversing the props?
or not?
Ta. :)
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Well it is the cheapest option in that it is not going to cost you anything so I would give it a go first.
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But while down there, I would check that the rudders were actually in the area where propwash can be expected, and extend them as suggested before with plasticard. If this shows an improvement, it becomes worth doing a prettier, permanent job.
As you have two rudders and two props, changing rotation probably wont make any difference, as some have said, this only changes things where there is a single prop.
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Actually I think you will find changing a single prop from clockwise to anti clockwise aint going to make a jot of difference Malcolm. :-\
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Okay, i think I'm going to leave well alone here.
The boat is not going to get a lot of water time in, so I think what I have will work for the time intended.
If I were going to use it more, and try manouvering trials, I might get more interested.
Thanks to all for yet another learning curve. O0 O0 :D
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hi there
Forget all about that has been said by these part time modellers :P .... listen, think of this....
Swap your propellers over; then, go to your transmitter. The channel you use for your throttle (speed control) should have a reverse function switch; depending on the transmitter, it should be in a small panel in the back or in a small panel on the front.
Flip the appropriate switch that corresponds with your throttle; this will now reverse your motors through your speed controller, so that you do not have to swap the wiring around on your motors. When you do a trial with the model, if you do not find any steering improvements - then, look at increasing the size of the rudders in overall depth.
Make sure that, when you look at your propellers with one of the blades facing downmost (downwards at its lowest point in the revolution) that the edge of the rudder is below this. This is the correct size in length for a rudder. If it is short, increase the depth temporarily with Plasticard then retry the steering of the model. This should improve the steering.
If it does improve the steerage; you have several options then of either manufacturing new rudders or cladding the existing rudders with Plasticard and fairing in to shape.
Try that. :D :D KEEP IT SIMPLE
Aye
john e
bluebird
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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, O0 O0
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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.
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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
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If you didn't spend all day sleeping John you could have saved us all a lot of hassle. >>:-( >>:-(
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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,
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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?
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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
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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.
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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.
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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. :D
Thanks for all the info, I have learnt a lot here.
Bob
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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
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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
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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
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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.
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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.
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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