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

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.
"Scout" wrote in message
...
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.

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

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

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

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

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

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