steering : rudder or not that is my question?

[ED66677]

This came to my mind as I'm designing/building my trans and rudder for my next boat.
I read somewhere that a lot of the drag on our FE boat is coming from the rudder, why wouldn't we get rid of it?
Just an idea...
But as most of our boat use flex drive I don't see (but I might be wrong) any reason why the flexible part between hull and strut/stinger could not be use to steer the prop?

[Simon.O.]

It is always good to see someone thinking about alternatives.
What you are suggesting ( I think ) is what is commonly called a steerable outdrive or strudder. I have one on one of my boats.
They are good BUT there are transmission losses associated with bending the flex cable to steer, not to mention the wear and possibility of early failiure.

Often when I think of "out of the box" ideas I do a pile of searching and find that the status quo is what achieves great results.
This is not to say that we have finished with developments.
New ideas come along from time to time and you may end up with one soon.

Please do not read this as a critisism as it is not meant to be one at all.
I do a LOT of out of the box thinking and have implemented some of these concepts in my builds.

Keep thinking
Keep trying
Keep learning
Stay having FUN !!

I do

[Steven Vaccaro]

All the steering units I have seen have a skeg to keep them going straight. I have shortened them, with no loss of handling, but have never cut one off to see what happened.

[ED66677]

In regards with handling, I think the vectorial thrust is a lot more efficient than a rudder, so IMO skeg is useless, but you pointed it out Steven is it necessary to keep it going straight, regardless of handling?

[G Doggett]

I remember reading in an early copy of RC Boat Modeler an article about a SAW record setting 6 cell mono that used a home built steerable outdrive.
The 'stinger' type drive pivotted on the back of the boat and simply used a flex cable in a nylon tube.
It did however still have a small skeg which I guess helped with stability but would cause some drag.
I'll see if I can find the article, but I have every copy of RC Boat Modeler since the first one in 1987 ( am I a model boat nut or what ) and don't have a clue which one it was in.
Graham.

[Simon.O.]

All the steering units I have seen have a skeg to keep them going straight. I have shortened them, with no loss of handling, but have never cut one off to see what happened.

I did !
The first one was on the OB on my tunnel, that was not a good move as it caused all sorts of handling problems.
The second was on one of my earlier cats, same thing again it was not ideal.
To qualify these experiments remember that the actual setup may not have been very good in the first place.

I believe that steerable drives have an application if done right and used for wide radius turns only, or better still in a saw application as Graham mentioned.

IMO the idea is to minimise drive losses while still getting the correct thrust angles and depths.
This is only achieved with flex or wire drive or in my early boats a uj (not ideal)
With these setups there is always going to be a loss of power.
Adding another vector to the equation will rob more power.

The question is now: What is the drag of the rudder vs power loss of an articlated drive.

Another thing that I consider is that effeciency improvements are more applicable to class boats where power has a set limit so you must get the most out of what you have.
For outright pond rockets (saw riggers) I believe they have more power that they know what to do with and the small drag from the rudder is offset by the massive power handed down by the motor.

I'll stop rambling for now and keep watching this topic.

[ED66677]

If I remember it well the drag is function of the projected (in direction of motion) section of the rudder, so keeping only a tiny skeg to keep it straight is fair and might save a lot of drag, I would be currious to compare the drag of a rudder to the drag of a sponson of a rigger???

My actual drive line is made of two rigid shaft/tube with bushing, one in the endbell that holds the 8XL and comes out of the transom, the other one in the stinger, the stinger is a L shape piece of alu (stinger body) in witch the same shaft/tube with busing goes, between these two shaft is a disposable piece of 4mm flex, the flex is protected with silicon fuel line that also keep it greased.

I will make another stinger body with a vertical shaft on top of it, to allow steering, it should not generate more power loss than without steering, at least in straight run!