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Old 13-06-2016, 19:52   #1
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Curious idiot question #1

Quote:
Originally Posted by deanwright
my dad used to say.
"there's no silly questions, just curious idiots "
So I got this response in my thread "cat question" And while it is fairly insulting to me, I also thought it was a very funny post.
So, I thought I would start a thread series asking my curious idiot questions, since I have about a ton of em.
So heres the first one.
Why is the wheel on a sailboat so big?

Now, in case you're thinking this is some kind of joke, it isn't. I really don't know, and am wondering why.
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Old 13-06-2016, 19:53   #2
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Re: Curious idiot question #1

Why is the wheel on a sailboat so big?

Leverage. Sailboats came long before power steering.
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Old 13-06-2016, 19:55   #3
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Re: Curious idiot question #1

A large wheel allows the helm to sit in the windward coaming and see the telltales.

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Old 13-06-2016, 19:57   #4
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Re: Curious idiot question #1

I don't think it's an idiot question. (Boy, am I contrary!)

If you look at old paintings of ships being steered in storms, you'll see that Turnin'Turtle was right, sometimes more than one man had to be on the helm at the same time.

And another snippet, even with the leverage supplied by a big wheel, if the boat is over powered, she'll round up even with full opposite lock.

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Old 13-06-2016, 20:03   #5
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Re: Curious idiot question #1

Depends on how the steering is set up. If it is manual, then you need either a big wheel for leverage or a smaller wheel with gearing (i.e. lots of turns of the wheel for a a given change of rudder angle) to push a large rudder against the forces involved. The large wheel and less turns is more practical.

If it is a hydraulic system, you can have a small wheel.
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Old 13-06-2016, 20:09   #6
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Re: Curious idiot question #1

I didn't realize the force was that great.
Thanx for the responses.
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Old 13-06-2016, 20:55   #7
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Re: Curious idiot question #1

With a balanced sail plan and a proper rudder, there isn't any helm resistance to speak of.

The only advantage in that scenario is being able to see the telltales as previously posted.
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Old 13-06-2016, 21:06   #8
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Re: Curious idiot question #1

Some of the old sailing vessels had two wheels, The odd one had three,

The two wheels could have four men turning the wheels at the same time, especially in storms,
Yes The force was that strong, Depends on the gearing as well, More gearing, more turns to turn the rudder, Less effort to turn the rudder,
More turns, Takes longer to turn the boat,

Good Example of two wheels, The boat passing Krakatoa when it blew up,
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Old 13-06-2016, 21:18   #9
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Re: Curious idiot question #1

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Yes The force was that strong, Depends on the gearing as well, More gearing, more turns to turn the rudder, Less effort to turn the rudder,
More turns, Takes longer to turn the boat,

Good Example of two wheels, The boat passing Krakatoa when it blew up,
I once sailed on 1939 72 foot wooden gaff rigged ketch. The wheel was 15 turns lock to lock.

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Old 13-06-2016, 21:22   #10
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Re: Curious idiot question #1

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Originally Posted by StuM View Post
Depends on how the steering is set up. If it is manual, then you need either a big wheel for leverage or a smaller wheel with gearing (i.e. lots of turns of the wheel for a a given change of rudder angle) to push a large rudder against the forces involved. The large wheel and less turns is more practical.

If it is a hydraulic system, you can have a small wheel.
Until it leaks out the oil, then you have no steering at all.
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Old 13-06-2016, 22:10   #11
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Re: Curious idiot question #1

We learned a lot over the centuries...

The force on the rudder and thus the wheel of an old vessel from the 1600's was immense compared to a similar size vessel today.
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Old 13-06-2016, 22:56   #12
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Re: Curious idiot question #1

On modern boats a lot of it is for looks (ie; wow mister, you sure do have a big...)

With old ships (and newer boats with old design), the rudder was hinged at the leading edge. As soon as you turn the rudder, the force of the water tries to force the rudder back in line with the keel. At higher speeds and/or sharp turn, this takes a lot of force.

With newer designs (spade style), maybe 40-45% of the rudder is in front of the rudder shaft. When you turn the water hitting that 40-45% tries to keep the rudder turning. Essentially it cancels out 40-45% of the force behind the shaft, so you only need 10-20% as much force from the steering mechanism.

If you really want to sit on either combing to watch the sails, a couple of 18" wheels will do fine. They can be hydraulic or mechanical.
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Old 14-06-2016, 00:31   #13
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Re: Curious idiot question #1

Without looking it up...

Not sure of the hydrodynamics on a rudder... but in aircraft with "flying stabilizers" (the whole tailplane is the control surface) the hinge line is at 25% to 27% because further back will have the control surface force itself to move more than commanded due to aerodynamic loading.

You want a little less area in front than just balancing to where it "wants" to stay centered or you have a very "twitchy" control.

I'd be surprised if the boat rudders are hinged much further back than 27%.

For a lot of forces the hydrodynamic effects are just "thick air" compared to aerodynamics.

Doesn't matter a lot about having the right number.... until someone wants to try to design their own rudder. Then you certainly don't want the hinge line too far back on the moveable surface.
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Old 14-06-2016, 02:16   #14
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Re: Curious idiot question #1

...re wheelsize:
if the lady can look over it - it's too small for her!
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Old 14-06-2016, 02:59   #15
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Re: Curious idiot question #1

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Originally Posted by TurninTurtle View Post
Without looking it up...

Not sure of the hydrodynamics on a rudder... but in aircraft with "flying stabilizers" (the whole tailplane is the control surface) the hinge line is at 25% to 27% because further back will have the control surface force itself to move more than commanded due to aerodynamic loading.

You want a little less area in front than just balancing to where it "wants" to stay centered or you have a very "twitchy" control.

I'd be surprised if the boat rudders are hinged much further back than 27%.

For a lot of forces the hydrodynamic effects are just "thick air" compared to aerodynamics.

Doesn't matter a lot about having the right number.... until someone wants to try to design their own rudder. Then you certainly don't want the hinge line too far back on the moveable surface.
Most planes, with the exception of some jet fighters and high performance models, use the equivalent of a skeg hung rudder with the hinge point at the leading edge of the rudder. In normal flight, the rudder is doing nothing and they don't generally perform a lot of extreme maneuvers, so it's an acceptable trade off. A boat rudder under sail is always trying to create lift, so a good hydrodynamic shape and angle is important.

When you talk about moving the hinge point back, it's almost always in relation to a spade rudder.

It's a little more complicated but in rough terms 50% ahead of the hinge point is the critical point. At that point, it will take no effort to turn the wheel as the turning force in front and the force behind will cancel out. This has a couple of bad results:
- You can't feel the forces on the rudder at all so it's not always clear what position it is in. This makes it hard to sail a straight line as there is no tactile feel.
- In the event of a failure, the rudder will wind up in a random position, so you may be stuck sailing in circles.

If you put the hinge point behind the center, it's even worse.
- As soon as you start turning the rudder, it will want to slam all the way over, so you will constantly be fighting it. While sailing, you always have the rudder turned slightly.
- In the event of a failure, it won't be random. As long as the rudder can move it will turn hard over and stay there.

People with skeg hung rudders often find out about this while backing at higher speeds. As soon as they start to turn, the rudder tries to rip the wheel out of the helmsman's hand and go hard over. (if you try this as an experiment be careful as it can cause damage)
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