65- by 32-foot catamaran 3200sqft of living space

Remodel

Super Anarchist
10,235
883
None
ah catwoman....

I'm old enough to know she was hot but which one was that? They kinda fucked up an awesome role.

Adam West, you've got to be kidding, even the most ardent George Michael toilet block recipient wouldn't find him hot.
I'm guessing Julie Newmar. Yowza!

julie+newmar.jpg


 
"given rudder force may result in greater yaw accelerations in a low mass boat than in a high mass boat, all else equal, but the loads on the rudder are identical in both cases"

What you're saying here is X is greater than Y, but then X must be equal to Y.
Na,

what he's actually saying is

if I apply a force X to the rudder, the force on the rudder will be X no matter what size the rudder or boat.

True, but not very useful., since it totally ignores the issue, which is how doe the size of rudder or boat affect the required size of X to achieve a given objective (e.g. turning at boat at a given rate in a given set of conditions).
The force on the rudder will be a combination of the following factors:

-Boat speed (except that is held constant in this exercise)

-Rotational mass moment of inertia of the boat about it's yaw axis. (that's a fancy description of weight and size)

-Hydrodynamic resistance to yaw based on hull shape. (For a daggerboard dinghy this is very low, on a big catamaran it's very high)

The reason that the forces are low on a small boat is that it is easy to turn; light at the ends and a nice pivot point in the middle.

And of course this all assumes the rudder doesn't stall; then there's a peak force equal to dragging a board sideways through the water.
However the force on the rudder can never exceed the force on the rudder.

Yes its a tautology, as was the underlined statement above, a given rudder force and the loads on the rudder are equivalent concepts.

The whole point about all these design cases is that they depend on the assumptions you are making.

In this case if we assume that we apply the same force on the rudder........ what will change is the effect that force has, and NOT the force on the rudder because we assumed that was the same.

Its not a totally irrelevant point.....it is easy to specify a rudder which will not break under normal steering loads if we neglect to specify that it must actually be able to turn the boat effectively.
Here's another irrelevant example:

I'll hold my hand up in the air and you can slap it as hard as you want.

You hold your hand up against your face, and let me slap it.

It's all just one hand slapping another, right?

Well, I agree that the hydrodynamic force on the rudder when the angle is changed may be similar in the two cases (until it stalls), but that's a very specific situation. In the real world, you need to consider all the other factors that come into play... What happens when a big wave slaps the rudder on the dinghy, as compared to the rudder on a massive boat? What about when the boat is already yawing, and you want the rudder to resist that? And as I said once before, there's more to the question than peak force... think energy, or force times time. Add impact loads, fatigue from repetitive forces and other considerations like how rotten the wood is where the hardware is attached, and it gets messy.

One option is to resort to 'Harley Davidson Engineering':

1. If it breaks, make it bigger.

2. If it sticks out, put chrome (or diamond plate) on it.

Except that the problem is that the 'if it breaks' could result in the boat being pounded on a lee shore.

I like the earlier phrase of "Fractal Failure": Doesn't matter if the rudder breaks, if it the boat can't move forward enough to need a rudder.

 

U20guy2

Super Anarchist
12,330
3
"given rudder force may result in greater yaw accelerations in a low mass boat than in a high mass boat, all else equal, but the loads on the rudder are identical in both cases"

What you're saying here is X is greater than Y, but then X must be equal to Y.
Na,

what he's actually saying is

if I apply a force X to the rudder, the force on the rudder will be X no matter what size the rudder or boat.

True, but not very useful., since it totally ignores the issue, which is how doe the size of rudder or boat affect the required size of X to achieve a given objective (e.g. turning at boat at a given rate in a given set of conditions).
The force on the rudder will be a combination of the following factors:

-Boat speed (except that is held constant in this exercise)

-Rotational mass moment of inertia of the boat about it's yaw axis. (that's a fancy description of weight and size)

-Hydrodynamic resistance to yaw based on hull shape. (For a daggerboard dinghy this is very low, on a big catamaran it's very high)

The reason that the forces are low on a small boat is that it is easy to turn; light at the ends and a nice pivot point in the middle.

And of course this all assumes the rudder doesn't stall; then there's a peak force equal to dragging a board sideways through the water.
However the force on the rudder can never exceed the force on the rudder.

Yes its a tautology, as was the underlined statement above, a given rudder force and the loads on the rudder are equivalent concepts.

The whole point about all these design cases is that they depend on the assumptions you are making.

In this case if we assume that we apply the same force on the rudder........ what will change is the effect that force has, and NOT the force on the rudder because we assumed that was the same.

Its not a totally irrelevant point.....it is easy to specify a rudder which will not break under normal steering loads if we neglect to specify that it must actually be able to turn the boat effectively.
Here's another irrelevant example:

I'll hold my hand up in the air and you can slap it as hard as you want.

You hold your hand up against your face, and let me slap it.

It's all just one hand slapping another, right?

Well, I agree that the hydrodynamic force on the rudder when the angle is changed may be similar in the two cases (until it stalls), but that's a very specific situation. In the real world, you need to consider all the other factors that come into play... What happens when a big wave slaps the rudder on the dinghy, as compared to the rudder on a massive boat? What about when the boat is already yawing, and you want the rudder to resist that? And as I said once before, there's more to the question than peak force... think energy, or force times time. Add impact loads, fatigue from repetitive forces and other considerations like how rotten the wood is where the hardware is attached, and it gets messy.

One option is to resort to 'Harley Davidson Engineering':

1. If it breaks, make it bigger.

2. If it sticks out, put chrome (or diamond plate) on it.

Except that the problem is that the 'if it breaks' could result in the boat being pounded on a lee shore.

I like the earlier phrase of "Fractal Failure": Doesn't matter if the rudder breaks, if it the boat can't move forward enough to need a rudder.
BTW if the rudder doesn't break - the transom or hardware holding it will. So why even bother posting about it? As long as FH sits in the mud flats as we start to see lows rolling through it won't matter given the rudders don't have enough water to be put down and the first good blow FH is done. They should have parked it up the Delta a week ago.

 

some dude

Super Anarchist
4,164
158
Na,

what he's actually saying is

if I apply a force X to the rudder, the force on the rudder will be X no matter what size the rudder or boat.

True, but not very useful., since it totally ignores the issue, which is how doe the size of rudder or boat affect the required size of X to achieve a given objective (e.g. turning at boat at a given rate in a given set of conditions).
The force on the rudder will be a combination of the following factors:

-Boat speed (except that is held constant in this exercise)

-Rotational mass moment of inertia of the boat about it's yaw axis. (that's a fancy description of weight and size)

-Hydrodynamic resistance to yaw based on hull shape. (For a daggerboard dinghy this is very low, on a big catamaran it's very high)

The reason that the forces are low on a small boat is that it is easy to turn; light at the ends and a nice pivot point in the middle.

And of course this all assumes the rudder doesn't stall; then there's a peak force equal to dragging a board sideways through the water.
However the force on the rudder can never exceed the force on the rudder.

Yes its a tautology, as was the underlined statement above, a given rudder force and the loads on the rudder are equivalent concepts.

The whole point about all these design cases is that they depend on the assumptions you are making.

In this case if we assume that we apply the same force on the rudder........ what will change is the effect that force has, and NOT the force on the rudder because we assumed that was the same.

Its not a totally irrelevant point.....it is easy to specify a rudder which will not break under normal steering loads if we neglect to specify that it must actually be able to turn the boat effectively.
Here's another irrelevant example:

I'll hold my hand up in the air and you can slap it as hard as you want.

You hold your hand up against your face, and let me slap it.

It's all just one hand slapping another, right?

Well, I agree that the hydrodynamic force on the rudder when the angle is changed may be similar in the two cases (until it stalls), but that's a very specific situation. In the real world, you need to consider all the other factors that come into play... What happens when a big wave slaps the rudder on the dinghy, as compared to the rudder on a massive boat? What about when the boat is already yawing, and you want the rudder to resist that? And as I said once before, there's more to the question than peak force... think energy, or force times time. Add impact loads, fatigue from repetitive forces and other considerations like how rotten the wood is where the hardware is attached, and it gets messy.

One option is to resort to 'Harley Davidson Engineering':

1. If it breaks, make it bigger.

2. If it sticks out, put chrome (or diamond plate) on it.

Except that the problem is that the 'if it breaks' could result in the boat being pounded on a lee shore.

I like the earlier phrase of "Fractal Failure": Doesn't matter if the rudder breaks, if it the boat can't move forward enough to need a rudder.
BTW if the rudder doesn't break - the transom or hardware holding it will. So why even bother posting about it? As long as FH sits in the mud flats as we start to see lows rolling through it won't matter given the rudders don't have enough water to be put down and the first good blow FH is done. They should have parked it up the Delta a week ago.
Exactly, Silly to get all worked up about it. The FH doesn't have any propulsion so you steer by turning the tow boat. Duh. If the mythical outboards ever show up you steer with those. And if any sails ever get put up, the boat will just spin around in circles, rutters or no rutters.

 

167149

Super Anarchist
Rudders, ok here's one Question for the bored injunears, difference and allowances for rudder design between sail, power and motor sailor, given the first relies on waterflow generated by motion be it forward backward or as this case may well be sideways, the 2nd relies on accelerated waterflow via propwash as well as motion while the third is a somewhere in the middle mix of the 2. Oh and Rod, I've already done a fair few bluewater miles on a 50'plus sailing cat so have a fair idea just how self destructing a raft can be

 

JohnMB

Super Anarchist
2,837
609
Evanston
"given rudder force may result in greater yaw accelerations in a low mass boat than in a high mass boat, all else equal, but the loads on the rudder are identical in both cases"

What you're saying here is X is greater than Y, but then X must be equal to Y.
Na,

what he's actually saying is

if I apply a force X to the rudder, the force on the rudder will be X no matter what size the rudder or boat.

True, but not very useful., since it totally ignores the issue, which is how doe the size of rudder or boat affect the required size of X to achieve a given objective (e.g. turning at boat at a given rate in a given set of conditions).
The force on the rudder will be a combination of the following factors:

-Boat speed (except that is held constant in this exercise)

-Rotational mass moment of inertia of the boat about it's yaw axis. (that's a fancy description of weight and size)

-Hydrodynamic resistance to yaw based on hull shape. (For a daggerboard dinghy this is very low, on a big catamaran it's very high)

The reason that the forces are low on a small boat is that it is easy to turn; light at the ends and a nice pivot point in the middle.

And of course this all assumes the rudder doesn't stall; then there's a peak force equal to dragging a board sideways through the water.
However the force on the rudder can never exceed the force on the rudder.

Yes its a tautology, as was the underlined statement above, a given rudder force and the loads on the rudder are equivalent concepts.

The whole point about all these design cases is that they depend on the assumptions you are making.

In this case if we assume that we apply the same force on the rudder........ what will change is the effect that force has, and NOT the force on the rudder because we assumed that was the same.

Its not a totally irrelevant point.....it is easy to specify a rudder which will not break under normal steering loads if we neglect to specify that it must actually be able to turn the boat effectively.
Here's another irrelevant example:

I'll hold my hand up in the air and you can slap it as hard as you want.

You hold your hand up against your face, and let me slap it.

It's all just one hand slapping another, right?

Well, I agree that the hydrodynamic force on the rudder when the angle is changed may be similar in the two cases (until it stalls), but that's a very specific situation. In the real world, you need to consider all the other factors that come into play... What happens when a big wave slaps the rudder on the dinghy, as compared to the rudder on a massive boat? What about when the boat is already yawing, and you want the rudder to resist that? And as I said once before, there's more to the question than peak force... think energy, or force times time. Add impact loads, fatigue from repetitive forces and other considerations like how rotten the wood is where the hardware is attached, and it gets messy.

One option is to resort to 'Harley Davidson Engineering':

1. If it breaks, make it bigger.

2. If it sticks out, put chrome (or diamond plate) on it.

Except that the problem is that the 'if it breaks' could result in the boat being pounded on a lee shore.

I like the earlier phrase of "Fractal Failure": Doesn't matter if the rudder breaks, if it the boat can't move forward enough to need a rudder.
GOOD LORD

my comment was very simple

The poster who made the comment I referenced made a tautological statment

Doug disagreed

There is no point disagreeing with a tautological statement so I said so.

Feel free to keep explaining why the tautological statement is irrelevant, but I thought I had covered that at the start.

If you think its wrong, you need to go back to the original statement and dissect it a little. :)

 

Somebody Else

a person of little consequence
7,638
805
PNW
Feel free to nest as many quotes as IPBoard allows.

We want to re-read everything over and over again and we are too stupit to infer context.

 

Pertinacious Tom

Importunate Member
62,064
1,884
Punta Gorda FL
Autonomous said:
Bizzaro rudder debate. Some here get it. For the others think duty cycle.

"Duty cycle is the proportion of time during which a component, device, or system is operated or stressed.

The more a circuit, machine or component is used, the sooner it will wear out. Therefore, the higher the duty cycle, the shorter the useful life, all other things being equal."

Great. We're talking about rutters and you have to bring up the doody cycle. I'd prefer to think of catwoman as not having one of those.

 

tls

Anarchist
693
0
You fellas keep trying to intuit what ought to be deduced; not unlike how HR engineered his cat.

Oh so now Newton's 2nd Law is "intuition"?

What cow college did you study injunearrinck at?

You fellas keep mistaking a textbook method for deriving how strong a rudder should be for the real-world forces on the rudder.

At the risk of repeating myself- this is why clever engineers often build stuff that breaks...

FB- Doug
Ah, back from 3 days of camping to see the ignorance has not abated. Glad to see you guys can keep the fires burning even if I am not around to stoke them.

At the risk of repeating myself, the force/work/energy needed to turn the boat is irrelevant, at least to a estimation to three or four significant digits. You just need the maximum V and the area distribution. There is a physics limit on how much force the water flow can impart to the rudder for a given flow velocity. In practice, virtually all boats will, at one time or another, apply that maximum force to the hull regardless of hull mass. This is because the rudder can almost always be turned at a higher angular rate than the boat can be turned (usually by an order of magnitude or so). So long as the rudder structure is appropriate for that force it will not break no matter what it is attached to. If the structure is not appropriate, it will break at some point no matter what it is attached to.

FB-Doug - explain to me the "real world forces on a rudder" that would allow it to impart more force than could be achieved at the max force AOA at a given velocity? The Fmax AOA is the AOA that yields the maximum length vector when the lift and drag components are vector added. How exactly does the rudder exceed that force without more velocity?

 
Ever'body's wrong, and I'm amazed no one's pointed it out yet.

As Rod stated, the FH has "ruTTers", not "ruDDers". All previous "rudder" posts are irrelevant.

Back to proposed sail plan.

 
Autonomous said:
Bizzaro rudder debate. Some here get it. For the others think duty cycle.

"Duty cycle is the proportion of time during which a component, device, or system is operated or stressed.

The more a circuit, machine or component is used, the sooner it will wear out. Therefore, the higher the duty cycle, the shorter the useful life, all other things being equal."
Perhaps. I was under the impression this discussion in particular was more of a doodie cycle.

 

tls

Anarchist
693
0
Autonomous said:
Bizzaro rudder debate. Some here get it. For the others think duty cycle.

"Duty cycle is the proportion of time during which a component, device, or system is operated or stressed.

The more a circuit, machine or component is used, the sooner it will wear out. Therefore, the higher the duty cycle, the shorter the useful life, all other things being equal."
I am not sure I understand your point. Obviously, a rudder that needs to be turned to large AOAs on a regular basis will have higher duty cycle. All else equal, a given rudder would have a higher duty cycle on a larger vessel. However, no one here is speculating on when the FH rudder will "wear out." The issue is structural failure from loads exceeding the structural strength in the "new" condition. In general, the rudder components that actually wear from high duty cycle are usually maintenance items (bearings, pintles, gudgeons), and the rudders themselves have no appreciable "wear" at all. If you were building the rudder from material that shows significant fatigue (certain aluminum alloys, or some types of composites in which the resin and fibers were poorly matched), then its duty cycle would be relevant. Building with wood or steel you will find that so long as forces are kept below yield, they maintain their structural properties for millions of cycles. If they exceed yield then they begin to break immediately. All that matters is whether peak loads stay under the yield strength of the rudder.

 

some dude

Super Anarchist
4,164
158
Autonomous said:
Bizzaro rudder debate. Some here get it. For the others think duty cycle.

"Duty cycle is the proportion of time during which a component, device, or system is operated or stressed.

The more a circuit, machine or component is used, the sooner it will wear out. Therefore, the higher the duty cycle, the shorter the useful life, all other things being equal."
Perhaps. I was under the impression this discussion in particular was more of a doodie cycle.
he said doodie

 
GOOD LORD

my comment was very simple

The poster who made the comment I referenced made a tautological statment

Doug disagreed

There is no point disagreeing with a tautological statement so I said so.

Feel free to keep explaining why the tautological statement is irrelevant, but I thought I had covered that at the start.

If you think its wrong, you need to go back to the original statement and dissect it a little. :)
I think you need to say "tautology" a few more times, cause it'll make you look smarter.

I notice you didn't take me up on the 'slap test'.

 

Monkey

Super Anarchist
10,885
2,504
Ever'body's wrong, and I'm amazed no one's pointed it out yet.

As Rod stated, the FH has "ruTTers", not "ruDDers". All previous "rudder" posts are irrelevant.

Back to proposed sail plan.
When a rutter breaks in the middle of a muddy bay, and no one's around to hear it, does it make a sound?
 




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