katysails wrote:

MC,

If you fo to all tht trouble of figuring things out every time you sail, do
you ever get to relax? You should have a hibernate setting on the right
side of your brain.

I think he is hibernating now, that's the best way to explain the flat
brain-waves... cranial nematodes again, maybe?


"Nav" wrote ...

Just for fun why not do a simple engineering calculation for us Doug?

Why, Navvie? Did one of your kids bring home a problem you can't help
him with?


For simplicity let's say the rig has mast without any stays.

Mast 20' vertical Boom 10' horizontal. Gooseneck 3' from base of mast
Vang attched to point 3' from goosneck. 200 lbs to be lifted.

What is the bending moment on the boom at the vang if the load is held
by the vang?
What is the shear stress on the boom the load is held by the vang?
What is the compression force of the boom at the vang attachment?

Is that mast perfectly vertical? Is the boom perfectly horizontal?


Now let me quickly solve for the topping lift case:

If a topping lift is used, the bending moment at the vang is 0.
If a topping lift is used, the shear stress is 0
If a topping lift is used, the boom compression is 200 x 10 /17 = 118

lbs.

??? The compression on the boom depends on the angle betweenthe topping
lift & the mast, thus you cannot solve the problem with the info given.
For the record, the compression on the boom would be the weight
multiplied by the cosine of the angle.

What is the maximum stress at the vang attachment point in each case?

That depends on how hard you're talking at it.

I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you don't
believe me, ask Scout.

DSK

DSK blustered:



katysails wrote:

MC,

If you fo to all tht trouble of figuring things out every time you
sail, do
you ever get to relax? You should have a hibernate setting on the right
side of your brain.


I think he is hibernating now, that's the best way to explain the flat
brain-waves... cranial nematodes again, maybe?


Ad_hominem?


"Nav" wrote ...

Just for fun why not do a simple engineering calculation for us Doug?


Why, Navvie? Did one of your kids bring home a problem you can't help
him with?


Nope.


For simplicity let's say the rig has mast without any stays.

Mast 20' vertical Boom 10' horizontal. Gooseneck 3' from base of mast
Vang attched to point 3' from goosneck. 200 lbs to be lifted.

What is the bending moment on the boom at the vang if the load is held
by the vang?
What is the shear stress on the boom the load is held by the vang?
What is the compression force of the boom at the vang attachment?


Is that mast perfectly vertical? Is the boom perfectly horizontal?


Read the question _slowly_.


Now let me quickly solve for the topping lift case:

If a topping lift is used, the bending moment at the vang is 0.
If a topping lift is used, the shear stress is 0
If a topping lift is used, the boom compression is 200 x 10 /17 = 118


lbs.


??? The compression on the boom depends on the angle betweenthe topping
lift & the mast, thus you cannot solve the problem with the info given.

Are you sure? The geometry _is_ defined.

For the record, the compression on the boom would be the weight
multiplied by the cosine of the angle.


Are you saying it is not 118 lbs in the topping lift case? Are you sure
it's the cosine of one of the angles of the triangle -just for the record?

What is the maximum stress at the vang attachment point in each case?


That depends on how hard you're talking at it.

I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you don't
believe me, ask Scout.

But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.


Cheers

Lot's of excitement but none for you -sorry I'm taken. Losing interest
in CM are you?

Cheers

Lady Pilot wrote:

Have you ever had a girlfriend, Nav?

You are incredibly smart...but incredibly boring at the same time.

Any excitement in your life?

LP (curious minds want to know)


"Nav" wrote in message
...

Just for fun why not do a simple engineering calculation for us Doug?

For simplicity let's say the rig has mast without any stays.

Mast 20' vertical Boom 10' horizontal. Gooseneck 3' from base of mast
Vang attched to point 3' from goosneck. 200 lbs to be lifted.

What is the bending moment on the boom at the vang if the load is held
by the vang?
What is the shear stress on the boom the load is held by the vang?
What is the compression force of the boom at the vang attachment?

Now let me quickly solve for the topping lift case:

If a topping lift is used, the bending moment at the vang is 0.
If a topping lift is used, the shear stress is 0
If a topping lift is used, the boom compression is 200 x 10 /17 = 118 lbs.

What is the maximum stress at the vang attachment point in each case?

Cheers

It took about 30 seconds to formulate a simple problem to show Doug the
forces involved. Is that a problem for you?

Cheers

Scout wrote:

Gee whiz Nav,
how long have you been waiting to work that one into a conversation?
Scout

"Nav" wrote in message
...

Just for fun why not do a simple engineering calculation for us Doug?

For simplicity let's say the rig has mast without any stays.

Mast 20' vertical Boom 10' horizontal. Gooseneck 3' from base of mast
Vang attched to point 3' from goosneck. 200 lbs to be lifted.

What is the bending moment on the boom at the vang if the load is held
by the vang?
What is the shear stress on the boom the load is held by the vang?
What is the compression force of the boom at the vang attachment?

Now let me quickly solve for the topping lift case:

If a topping lift is used, the bending moment at the vang is 0.
If a topping lift is used, the shear stress is 0
If a topping lift is used, the boom compression is 200 x 10 /17 = 118 lbs.

What is the maximum stress at the vang attachment point in each case?

Cheers

katysails wrote:

MC,

If you fo to all tht trouble of figuring things out every time you sail, do
you ever get to relax? You should have a hibernate setting on the right
side of your brain.


Well Kook, when you are on a nice reach on a long passage you have
plenty of time to think about how your boat works. This put you in good
stead for emergencies. If, for example, you don't understand the forces
on a rigid vang how would you rig an emergency replacement that will not
break? In any case, the trig is just lioke a Nav exercise...

Geddit? :-)

Cheers

"Nav" wrote in message
...
Losing interest
| in CM are you?

Are you kidding me... she came to her senses long ago and realized I was
truly beneath her considerations!
.... mind you not until she broke her second ice pick!! ;-)

CM

I don't believe you can type that fast.
Scout

"Nav" wrote in message
...
It took about 30 seconds to formulate a simple problem to show Doug the
forces involved. Is that a problem for you?

Cheers

Scout wrote:

Gee whiz Nav,
how long have you been waiting to work that one into a conversation?
Scout

"Nav" wrote in message
...

Just for fun why not do a simple engineering calculation for us Doug?

For simplicity let's say the rig has mast without any stays.

Mast 20' vertical Boom 10' horizontal. Gooseneck 3' from base of mast
Vang attched to point 3' from goosneck. 200 lbs to be lifted.

What is the bending moment on the boom at the vang if the load is held
by the vang?
What is the shear stress on the boom the load is held by the vang?
What is the compression force of the boom at the vang attachment?

Now let me quickly solve for the topping lift case:

If a topping lift is used, the bending moment at the vang is 0.
If a topping lift is used, the shear stress is 0
If a topping lift is used, the boom compression is 200 x 10 /17 = 118
lbs.

What is the maximum stress at the vang attachment point in each case?

Cheers

He uses a secretary ... she types about 120 wpm.

CM



"Scout" wrote in message
...
| I don't believe you can type that fast.
| Scout

I'll bet she just loves being forced into asa ****ing contests.
Scout

"Capt. Mooron" wrote in message
...
He uses a secretary ... she types about 120 wpm.

CM



"Scout" wrote in message
...
| I don't believe you can type that fast.
| Scout

Even so, not including the introduction and the "cheers" that post was 146
words.
That's 73 seconds of typing.
Scout

"Capt. Mooron" wrote in message
...
He uses a secretary ... she types about 120 wpm.

CM



"Scout" wrote in message
...
| I don't believe you can type that fast.
| Scout

Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

I wonder what "formuilating a problem" has to do with typing?

Cheers



Capt. Mooron wrote:
Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

I've nver heard of that part of the anatomy being called a
"consideration" although in contract law that can be money...

Cheers

Capt. Mooron wrote:

"Nav" wrote in message
...

Losing interest

| in CM are you?

Are you kidding me... she came to her senses long ago and realized I was
truly beneath her considerations!
... mind you not until she broke her second ice pick!! ;-)

CM

Nav wrote:
Ad_hominem?

Yep. Couldn't happen to a nicer guy, too.

After the way you have acted, to get all nose-in-the-air about my poking
fun at your obsessive behavior is rather funny.


Are you sure? The geometry _is_ defined.

You're right. Lesson 1- always look the problem over thoroughly.


For the record, the compression on the boom would be the weight
multiplied by the cosine of the angle.


Are you saying it is not 118 lbs in the topping lift case?

Are you saying it's not the cosine of the angle formed by the topping
lift? Tell you what, go down the hall and ask one of the engineering
profs... if any will speak to you...

I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you
don't believe me, ask Scout.


But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.

Well, it is only a few minutes to draw up a free body diagram. I did a
rough one earlier, but it will take longer to do it on the comuter and
post it. Another job for tomorrow....

I wonder why the boom vang situation bothers you so much, or why you are
*so* sure that a solid vang cannot lift a heavy weight. I've seen it
done several times on several different boats, so obviously it can.

Hey, I got an idea... let's have a little wager on it... no wait, you
don't pay up when you lose...

Fresh Breezes- Doug King

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.

"DSK" wrote in message
.. .
Nav wrote:
Ad_hominem?

Yep. Couldn't happen to a nicer guy, too.

After the way you have acted, to get all nose-in-the-air about my poking
fun at your obsessive behavior is rather funny.


Are you sure? The geometry _is_ defined.

You're right. Lesson 1- always look the problem over thoroughly.


For the record, the compression on the boom would be the weight
multiplied by the cosine of the angle.


Are you saying it is not 118 lbs in the topping lift case?

Are you saying it's not the cosine of the angle formed by the topping
lift? Tell you what, go down the hall and ask one of the engineering
profs... if any will speak to you...

I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you
don't believe me, ask Scout.


But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.

Well, it is only a few minutes to draw up a free body diagram. I did a
rough one earlier, but it will take longer to do it on the comuter and
post it. Another job for tomorrow....

I wonder why the boom vang situation bothers you so much, or why you are
*so* sure that a solid vang cannot lift a heavy weight. I've seen it
done several times on several different boats, so obviously it can.

Hey, I got an idea... let's have a little wager on it... no wait, you
don't pay up when you lose...

Fresh Breezes- Doug King

"Nav" wrote:
Lot's of excitement but none for you -sorry I'm taken.

No need to apologize. You're not my type; I like smart guys, but they have
to be funny, interesting and witty. I haven't seen much of that in your
posts.

Losing interest
in CM are you?

Why do you want to know?

LP

"Capt. Mooron" wrote:

"Nav" wrote: Losing interest
| in CM are you?

Are you kidding me... she came to her senses long ago and realized I was
truly beneath her considerations!
... mind you not until she broke her second ice pick!! ;-)

Forget the ice pick...I've invested in a sturdy axe! ;-D

LP

Excuse me....I did not give you permission to abuse MC...only I am allowed
to abuse him....go back to Mooron...he's got a tougher hide....
"Lady Pilot" wrote in message
news:VUbXc.3970$gl.2552@okepread07...

"Nav" wrote:
Lot's of excitement but none for you -sorry I'm taken.

No need to apologize. You're not my type; I like smart guys, but they
have
to be funny, interesting and witty. I haven't seen much of that in your
posts.

Losing interest
in CM are you?

Why do you want to know?

LP

DSK wrote:
Nav wrote:

Ad_hominem?


Yep. Couldn't happen to a nicer guy, too.

After the way you have acted, to get all nose-in-the-air about my poking
fun at your obsessive behavior is rather funny.


Snort.


Are you sure? The geometry _is_ defined.


You're right. Lesson 1- always look the problem over thoroughly.


Progress!


For the record, the compression on the boom would be the weight
multiplied by the cosine of the angle.


Are you saying it is not 118 lbs in the topping lift case?


Are you saying it's not the cosine of the angle formed by the topping
lift? Tell you what, go down the hall and ask one of the engineering
profs... if any will speak to you...

So you are maintaining it's the "cosine" of the angle and it's not as I
posted, 118 lbs. Interesting.


I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you
don't believe me, ask Scout.



But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.


Well, it is only a few minutes to draw up a free body diagram. I did a
rough one earlier, but it will take longer to do it on the comuter and
post it. Another job for tomorrow....



I look forward to seeing your solution. While you are at it look at that
"cosine" you so like. Perhaps you will then see why I did use a "cosine"
or any other trig. function to calculate the compression.


I wonder why the boom vang situation bothers you so much, or why you are
*so* sure that a solid vang cannot lift a heavy weight. I've seen it
done several times on several different boats, so obviously it can.


No one said it could not. The question was one of seamanship and
appropriate use of equipment, spars and rigging. Do you deny that a
given weight that will fold a boom in the vang lift will be easily
lifted by the boom if a topping lift is used?



Cheers

Lady Pilot wrote:

"Nav" wrote:

Lot's of excitement but none for you -sorry I'm taken.


No need to apologize. You're not my type;

The feeling is quite mutual and moot in my case.

Cheers

"katysails" wrote:

Excuse me....I did not give you permission to abuse MC...only I am allowed
to abuse him....

Sheeze, that's not fair! I was having fun!

go back to Mooron...he's got a tougher hide....

How do you know? Have you checked out his muscles lately? :-)

So are you saying that MC is all flabby? heheee

LP

"Nav" wrote:

The feeling is quite mutual and moot in my case.

You have feelings? I'm astonished!

LP

Of course you are. Every time you blink it's "Hello world"...

Cheers


Lady Pilot wrote:

"Nav" wrote:


The feeling is quite mutual and moot in my case.


You have feelings? I'm astonished!

LP

On Wed, 25 Aug 2004 20:28:30 -0300, "Capt. Mooron"
wrote:

He uses a secretary ... she types about 120 wpm.

CM

Somebody's tag line from the past.
"I cna ytpe 300 wrods pre mniuet!"
lol
Mark W

And I'm wondering what the formulation time has to do with how long you've
been waiting to work it into a conversation.
Scout

"Nav" wrote in message
...
I wonder what "formuilating a problem" has to do with typing?

Cheers



Capt. Mooron wrote:
Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

Hey Doug,
My physics teaching partner is a lot like MC. He's an engineer, but with a
strong military (Navy) background. He loves to "test me" only he seems a bit
less condescending than MC. I'm sure MC is a likeable guy if you can get
past his need to out-math everyone around him. And of course, if you were
female he'd be a lot nicer (song to the tune of Desperado).
With my partner and I, it's a classic case of engineer versus technician.
I'm not always right, but neither is he. We don't hold back debating in
front of the kids either, as we feel they should see what that people often
disagree in the workplace. Every so often we'll take a low shot at each
other. I might say something like, "yes, but when I design something, it has
to actually work." I won't tell you what he says, lol.
My advice is to not take things/people too seriously in this, or any, NG.

Scout
"Everyone wants to design and build, no one wants to do maintenance." K.
Vonnegut


"DSK" wrote
I gather that you have never heard of a "Free Body Diagram"? Freshman
engineering stuff. That is the way to solve such problems. If you
don't believe me, ask Scout.

But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.

gonefishiing wrote:
refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?

No, IIRC it's the integral of the solid cross section area distance from
the axis. That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.

I can refer you to a pretty good text book.

but this is for rectangular sections right?
how do you calculate this for an oval section?

Personally, I don't. I look it up! But this is also not foolproof, you'd
be amazed how many mfg'rs fudge their specs (or maybe they can't do math).

Hope this helps.

Fresh Breezes- Doug King

"DSK" wrote in message
. ..
gonefishiing wrote:
refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?

No, IIRC it's the integral of the solid cross section area distance from
the axis. That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.

MEANING TO THE EXTREME OUTER FIBERS IN BOTH AXIS?

I can refer you to a pretty good text book.

but this is for rectangular sections right?
how do you calculate this for an oval section?

Personally, I don't. I look it up! But this is also not foolproof, you'd
be amazed how many mfg'rs fudge their specs (or maybe they can't do math).

YEAH BEEN THERE RECENTLY: IT IS ALSO CALLED EXPENSIVE WHEN YOU DISCOVERED
THEIR PUBLISHED ERRORS.

Hope this helps.

Fresh Breezes- Doug King

Nav wrote:
Snort.

One of your more clever remarks.


Are you sure? The geometry _is_ defined.


You're right. Lesson 1- always look the problem over thoroughly.

Actually, on 2nd look, you're wrong. It isn't, unless you *assume* the
mast is perfectly vertical and the boom perfectly horizontal.


Are you saying it is not 118 lbs in the topping lift case?

Probably not. With the ratios you give (assuming vertical mast & level
boom, since you don't seem capable of defining the problem correctly)
the compression is going to be somewhat less than 1/2 the weight.

And, if you look closely, you'll see that the tension on the topping
lift is *more* than the weight! Hello! How did that happen?

Wait there's more... a mysterious force has appeared on the mast!
Apparently the pulling of the topping lift and the pushing of the boom
has run amok! HELP HELP!


I gather that you have never heard of a "Free Body Diagram"?
Freshman engineering stuff. That is the way to solve such problems.
If you don't believe me, ask Scout.


But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.

I see. You're playing stalker again. Considering that you've never won
even once, is this wise?

Can *you* solve the problem, Navvie? Go ahead, ask for some advice from
down the hall! This mysterious new stress on the mast and the resolution
of forces is not obvious (although it's not terribly difficult either)
and leads to some interesting conclusions, all of which support what I
have said all along.


Well, it is only a few minutes to draw up a free body diagram.

http://community.webshots.com/photo/...79893018mpZKNO

Actually it took the longest to convert the file and upload it. What a
PITA. All to prove a stupid point.

... The question was one of seamanship and
appropriate use of equipment, spars and rigging. Do you deny that a
given weight that will fold a boom in the vang lift will be easily
lifted by the boom if a topping lift is used?

So, I take that you've folded up a boom trying to lift something? Can we
assume that you learned nothing from it, other than "don't"?

Fresh Breezes- Doug King

Scout wrote:
Hey Doug,
My physics teaching partner is a lot like MC. He's an engineer, but with a
strong military (Navy) background. He loves to "test me" only he seems a bit
less condescending than MC. I'm sure MC is a likeable guy if you can get
past his need to out-math everyone around him.

The thing I dislike about Navvie, apart from his condescension, is that
he's so often wrong, and he gives bad advice while pontificating. He has
little clue of how little clue he has, and no interest in learning.

I come here mostly to learn, partly for fun... he's no fun and has
nothing to teach other than dendrite morphology (or is it morphadite
endrology?).

With my partner and I, it's a classic case of engineer versus technician.

That's always a tough line to straddle.

I'm not always right, but neither is he.

Nobody is *always* right. It can be fun to pretend though.

... We don't hold back debating in
front of the kids either, as we feel they should see what that people often
disagree in the workplace. Every so often we'll take a low shot at each
other. I might say something like, "yes, but when I design something, it has
to actually work." I won't tell you what he says, lol.

I can guess.

My advice is to not take things/people too seriously in this, or any, NG.

There is a good bit to be learned here... with guys like Jeff, Oz1, Pony
X, Ol' Thom, Bart, not to mention the pros Rick & Schoonertrash (when he
isn't discussing history) & Shen44 & otn, there are more serious sailing
and cruising discussions here than any other place on the web I've
checked regularly.

But the personality clashes are minor & petty. What makes you think I
take any of it seriously?


"Everyone wants to design and build, no one wants to do maintenance." K.
Vonnegut

That's the honest truth.

Regards
Doug King

No, IIRC it's the integral of the solid cross section area distance from
the axis. That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.


gonefishiing wrote:
MEANING TO THE EXTREME OUTER FIBERS IN BOTH AXIS?

No, all fibers along the tension/compression axis. That's why it's an
integral.


but this is for rectangular sections right?
how do you calculate this for an oval section?

Personally, I don't. I look it up! But this is also not foolproof, you'd
be amazed how many mfg'rs fudge their specs (or maybe they can't do math).


YEAH BEEN THERE RECENTLY: IT IS ALSO CALLED EXPENSIVE WHEN YOU DISCOVERED
THEIR PUBLISHED ERRORS.

I hope nobody got hurt. This is called "letting your customers do your
failure mode testing." It's very popular with software firms, too ;)

Regards
Doug King

"Lady Pilot" wrote in message

| Forget the ice pick...I've invested in a sturdy axe! ;-D

Heh... that's for cutting woody things...

OUCH!

CM

I'm wondering what you are talking about.

Cheers

Scout wrote:

And I'm wondering what the formulation time has to do with how long you've
been waiting to work it into a conversation.
Scout

"Nav" wrote in message
...

I wonder what "formuilating a problem" has to do with typing?

Cheers



Capt. Mooron wrote:

Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

DSK wrote:

Nav wrote:


Are you sure? The geometry _is_ defined.



You're right. Lesson 1- always look the problem over thoroughly.


Actually, on 2nd look, you're wrong. It isn't, unless you *assume* the
mast is perfectly vertical and the boom perfectly horizontal.


Assume nothing. If it were not vertical or horizontal the angle would be
given. One wonders if you ever took any engineering courses...
Introducing "perfectly" shows a clear lack of engineering expertise and
an attempt to smoke screen. It's pretty clear you can't do it can you?


Are you saying it is not 118 lbs in the topping lift case?


Probably not. With the ratios you give (assuming vertical mast & level
boom, since you don't seem capable of defining the problem correctly)
the compression is going to be somewhat less than 1/2 the weight.

And, if you look closely, you'll see that the tension on the topping
lift is *more* than the weight! Hello! How did that happen?

Wait there's more... a mysterious force has appeared on the mast!
Apparently the pulling of the topping lift and the pushing of the boom
has run amok! HELP HELP!


Yes, you need help -the diagram is pretty much worthless and you've not
shown your incorrect "cosine" anyway . I'd say you just failed freshman
engineering.


I gather that you have never heard of a "Free Body Diagram"?
Freshman engineering stuff. That is the way to solve such problems.
If you don't believe me, ask Scout.



But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.



Actually it took the longest to convert the file and upload it. What a
PITA. All to prove a stupid point.


The point being you can't draw a proper free body diagram or solve the
problem?

... The question was one of seamanship and appropriate use of
equipment, spars and rigging. Do you deny that a given weight that
will fold a boom in the vang lift will be easily lifted by the boom if
a topping lift is used?


So, I take that you've folded up a boom trying to lift something? Can we
assume that you learned nothing from it, other than "don't"?


Such vivid imagination. Assume what you like but it's obvious from this
thread to any engineer that you don't even begin to understand basic
engineering.

Cheers

DSK wrote:

gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?


No, IIRC it's the integral of the solid cross section area distance from
the axis.

Perhaps term you are groping for is "section moment"? You can look it up
on the web.

That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.

I think you may be confusing a truss with a section. For bending in
plane, the most rigid section per unit weight is close to a T
section with the top under compression and the bulb (or smaller bottom
plate) at the bottom in tension. If the direction can be up and down
this becomes the familiar I beam. For compression, a circle (tube) is
generally best as again, it places most material away from the axis for
all planes containing the axis. This important as the failure mode is
almost always buckling and not material compression. For a combination
of compression and bending the best solution lies between these cases so
we see egg shapes and ovals but the object is always to place as much
material from the axis as needed to contain the stress well below a
yield stress.

Hope this helps.

Cheers

gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

You can use a simple rule of thumb. If you know the moment of intertia
for a box section of the same wall thickness and outside dimensions the
moment of inertial of the tube or ellipse that has the same dimension is
about 14% less.

Hope this gives you what you want.

Cheers

as the tune
gonefishiing wrote:
nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:


refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

So, I take that you've folded up a boom trying to lift something? Can
we assume that you learned nothing from it, other than "don't"?


Nav wrote:
Such vivid imagination.

Well, I have seen booms supported by rigid vangs that didn't fold up, so
obviously it can be done... if you do it right.

You think it can't be done, why? Conclusion: you did it wrong, and
decided it was impossible.


.... it's obvious from this
thread to any engineer that you don't even begin to understand basic
engineering.

Funny you should say that, since you show no comprehension of how to
read the diagram, yet you pass judgement on my competence. The
resolution of forces is not obvious but it's also not rocket science.

If OTOH you *do* have some clue what you're talking about, tell us what
the mysterious symbol next to the mast represents.

DSK