"DSK" wrote in message

| Why not? If the boom can take the torsion in one direction, then unless
| it is a very weird asymmetric structure, then it will take the same in
| the opposite direction.

This is where you stray from engineering principal... that is not the case
at all nor is it the rule.

| Sure it is. It's exactly the same in both directions.

No Doug... it is most assuredly not the same in both directions if only by
the points of compression
|
| What I'm saying is the same as saying if you can stand on a beam (let's
| say a 2x6) between two sawhorses, and it doesn't break, then you can
| turn the beam over and still stand on it. You're saying that it doesn't
| work that way, if the beam doesn't break one way then it will definitely
| break the other...

That's not at all what I said and again you are attempting to introduce the
boom as a factor... that is not good methodology for what we are discussing
here.... forget the boom or assume it indestrutructable and unbendable.|

| The max forces are limited by the righting moment of the boat. On a 30
| footer, it doesn't need to be that massive. On bigger boats... take a
| look at the vangs on IACC racers...

Nobody is discussing righting moment here Doug... we are discussing the
ability of basic mathematics in regards to the placement of the vang and the
loads you expect it to encounter.


| Actually, I have. It's not that complicated. Try drawing out a diagram
| of moments. If you need a refresher
|
http://www2.umist.ac.uk/construction...xp/sfbmdex.htm
|

No Doug... it's not that I refuse to seek knowledge but this time you had
better be able to logically explain your theory to me without a jaxxian
reflex to google proof that may or may not have bearing on what we are
discussing.



| No, it isn't... but it is holding down 100% of the leach tension, which
| is very large. It also takes all the load of the mainsheet when hauled
| in tight to go to windward. If it doesn't break when you honk down on an
| 8:1 purchase, then it should hold at least 8X your honking strength

No Doug... it is most certainly NOT holding down 100% of the leech
tension... that load is divided with a bigger factor attributed to the
mainsheet.
|
|
| For using the boom as a lifting device.... you will stress the vang
unduly
| with a set-up located that far back on the load arm.
|
| ???

Well come on now Doug.... it's basic common sense engineering principal!

| ... It's not designed for
| that.
|
| It should be. Anything less would not be safe for sailing IMHO.

No it's not... it's designed as a VANG!


CM

| Why not? If the boom can take the torsion in one direction, then unless
| it is a very weird asymmetric structure, then it will take the same in
| the opposite direction.

Capt. Mooron wrote:
This is where you stray from engineering principal... that is not the case
at all nor is it the rule.

Oh? Are you saying that a symmetric structural member is stronger one
way than the other? If you nail a board into a frame, you have to be
careful to put it label side up or something?




| Sure it is. It's exactly the same in both directions.

No Doug... it is most assuredly not the same in both directions if only by
the points of compression

Well, go explain that to Newton. He had a little to say on the subject.

.... forget the boom or assume it indestrutructable and unbendable.

OK


| The max forces are limited by the righting moment of the boat. On a 30
| footer, it doesn't need to be that massive. On bigger boats... take a
| look at the vangs on IACC racers...

Nobody is discussing righting moment here Doug...

Well, if we're not discussing the strength of the boom, nor the limit of
force on the whole system, then the only thing to complain about it the
compressive strength of the vang itself (which with a proper one, should
not be an issue) or the strength of the connections between vang, mast,
& boom.

If you break the gooseneck, then it probably wasn't strong enough
anyway. The vang connections take greater strain than the gooseneck (due
to the greater leverage) and thus they have to be stronger yet. So that
rules them out.

Now all you're left with is the strength of the vang itself.

How about a hydraulic cylinder? Some are. How about a very thick solid
SS turnbuckle with machine threads? Some are. That leaves the little
fiberglass rod ones (which I agree are not going to hold up much load)
and the spring loaded locking kind. I suggest you take a look at the
specs on several and see if you can't find one or two that look strong
enough to hold up a substantial load. They're there.



... we are discussing the
ability of basic mathematics in regards to the placement of the vang and the
loads you expect it to encounter.

Not really. You were trying to obfuscate the basic point that a vang
needs to be strong enough to stand up to hard sailing, and if it will do
that, it is almost certainly strong enough the other way too (unless
it's one of those wimpy hen-pecked little fiberglass rod ones).

| For using the boom as a lifting device.... you will stress the vang
unduly
| with a set-up located that far back on the load arm.
|
| ???

Well come on now Doug.... it's basic common sense engineering principal!

It can't be that basic, I have no clue what you're talking about.
Doesn't seem to pertain to vangs, though.


| ... It's not designed for
| that.
|
| It should be. Anything less would not be safe for sailing IMHO.

No it's not... it's designed as a VANG!

I guess a tackle employed as a vang would not be strong enough to use
for anything else?

I do one thing... you can't push a rope.

DSK

Doug,

I mentioned early in this discussion that with a topping lift hoisting
boom, the boom only positions the location of hoist. There is very, very
little force on the boom. The hoist is on the topping lift.

Mooran re-stated this.

You are the one insisting the force is the same on the end of the boom
supported on the other end by a Vang and a gooseneck. We say BS and sign
off.

Ole Thom

Hi Thom

Actually the force is revealed as compression on the boom in the topping
lift case and bending in the vang lifgt case. I wonder how many booms
Dog has bent lifting loads that way??? In our case, the solid vang only
serves to hold the boom up is the sail is dropped (and no topping lift
used). Just another thought, do you suppose Doug thinks that compressive
and tensile strengths are the same in symmetrical structures???

Cheers

Thom Stewart wrote:

Doug,

I mentioned early in this discussion that with a topping lift hoisting
boom, the boom only positions the location of hoist. There is very, very
little force on the boom. The hoist is on the topping lift.

Mooran re-stated this.

You are the one insisting the force is the same on the end of the boom
supported on the other end by a Vang and a gooseneck. We say BS and sign
off.

Ole Thom

Thom Stewart wrote:
Doug,

I mentioned early in this discussion that with a topping lift hoisting
boom, the boom only positions the location of hoist. There is very, very
little force on the boom. The hoist is on the topping lift.

Mooran re-stated this.

You are the one insisting the force is the same on the end of the boom
supported on the other end by a Vang and a gooseneck. We say BS and sign
off.

In other words, you're saying that 100# on the end of the boom supported
by a topping lift is not the same as 100# on the end of the boom
supported by a solid vang?

OK but I'm a little confused... how does the weight know the difference?

DSK

"DSK" wrote in message
| In other words, you're saying that 100# on the end of the boom supported
| by a topping lift is not the same as 100# on the end of the boom
| supported by a solid vang?
|
| OK but I'm a little confused... how does the weight know the difference?

Doug.... the weight remains the same that's not the point. The load bearing
forces between those delivered to the topping lift and the boom acts as a
"spreader"... while with the vang all the load is delivered to the boom and
the vang is subjected to the magnified loads.... in other words the load is
delivered to the vang and the leverage is delivered by the boom. That's why
I mentioned the fulcrum earlier.

When the boom is the spreader the force is compressive and much less than
the forces applied to the vang in such a situation. The topping lift bears
the entire load. The vang supports the boom distal to the load point so as
to magnify the bearing force.

Can you see the point of my argument now??

CM

Capt. Mooron wrote:
Doug.... the weight remains the same that's not the point.

Oh.

... The load bearing
forces between those delivered to the topping lift and the boom acts as a
"spreader"...

You mean the boom takes the load as compression... guess what, so does
the mast, and all the rigging, which transfers it to the hull. The load
is the same, the total amount of stress is the same, except that much of
the rigging is pre-loaded. And the compression on the mast is likely to
be a multiple of the weight involved.


...while with the vang all the load is delivered to the boom and
the vang is subjected to the magnified loads.... in other words the load is
delivered to the vang and the leverage is delivered by the boom. That's why
I mentioned the fulcrum earlier.

OK. It's still not a good explanation and tends to muddy the engineering
points.

The weight is the same... check.

With a topping lift, you seem to think that the boom has very little
stress on it. That is not the case.

Imagine this... replace the boom with your arms. Hang a 100# weight from
a long rope, and then try to push it 12' away from hanging straight
down. Depending on the angle to the point of hoist, you could end up
with more than 100 pounds of force.



When the boom is the spreader the force is compressive and much less than
the forces applied to the vang in such a situation. The topping lift bears
the entire load.

No it does not. Do you think the force magically goes away because there
is a topping lift?


Can you see the point of my argument now??

Yes, can you see the error you're making? You should make a diagram of
the forces involved. It will help you visualize the situation properly.

With a solid vang, that the force on the boom vang is greater than the
weight is not (or should not be) a problem, no more than the compression
on an old-timey noodley boom is. They're designed for that. If the gear
is designed & built properly for it's use, then it is fine.

Ever notice how on modern boats, the boom is not just s shorter section
of the same type extrusion as the mast? There are engineering reasons
for that (plus it looks cool).

Fresh Breezes- Doug King

CM

"DSK" wrote in message
| You mean the boom takes the load as compression... guess what, so does
| the mast, and all the rigging, which transfers it to the hull. The load
| is the same, the total amount of stress is the same, except that much of
| the rigging is pre-loaded. And the compression on the mast is likely to
| be a multiple of the weight involved.

No Doug.... I believe that assumption to be incorrect... you fail to
incorporate the dispersion of the load from the mast head to compression of
the mast and delivery of portions of the load to the shrouds. When you
transfer the load to the vang alone [ via the boom].. the mast is only
subject to a side load from the vang fitting and all the force is supported
by the boom/vang. None of the load is distributed to the entire mast or the
shrouds. In other words any portion of the mast above the boom is not
utilized in the dispersion of the forces generated by the bearing loads.


|
|
| ...while with the vang all the load is delivered to the boom and
| the vang is subjected to the magnified loads.... in other words the
load is
| delivered to the vang and the leverage is delivered by the boom. That's
why
| I mentioned the fulcrum earlier.
|
| OK. It's still not a good explanation and tends to muddy the engineering
| points.

The only thing muddy here is your refusal to approach this with an open
mind..


|
| The weight is the same... check.
|
| With a topping lift, you seem to think that the boom has very little
| stress on it. That is not the case.

I never stated very little stress.. I stated much less stress by a greater
margin than with the vang based option.

|
| Imagine this... replace the boom with your arms. Hang a 100# weight from
| a long rope, and then try to push it 12' away from hanging straight
| down. Depending on the angle to the point of hoist, you could end up
| with more than 100 pounds of force.

Ridiculous... the force required to push it away would be far less than the
force required to keep the arm level while applying force to a point just
aft of my elbow!
|
|
|
| When the boom is the spreader the force is compressive and much less
than
| the forces applied to the vang in such a situation. The topping lift
bears
| the entire load.
|
| No it does not. Do you think the force magically goes away because there
| is a topping lift?

It does not go away nor did I say it did... I said the load is more evenly
distributed over a greater span.. Mast, Boom, Topping lift, Shrouds... etc.
This of course increases the ability of the rig to undertake the bearing
forces. Gawd forbid you would ever be required to calc break-out forces
generated by excavators.


|
|
| Can you see the point of my argument now??
|
| Yes, can you see the error you're making? You should make a diagram of
| the forces involved. It will help you visualize the situation properly.

I am most definitely not in error here Doug... you are... swallow your pride
and look at this problem with an eye to structural engineering. I am
visualizing the situation and after much thought and further toying with the
idea I came to the conclusion that you are not correct in your theory
regarding forces delivered to the vang. You have yet to present a viable
defense for your position on this while I have offered several sound,
reasoned, and logical counterpoints to your pretense.

|
| With a solid vang, that the force on the boom vang is greater than the
| weight is not (or should not be) a problem, no more than the compression
| on an old-timey noodley boom is. They're designed for that. If the gear
| is designed & built properly for it's use, then it is fine.

No Doug... it's not the case at all.... the vang is badly situated to handle
the loads you intend to place to it. The topping lift offers a much better
and more efficient distribution of the load ... thus increasing it's ability
to handle much greater loads.

|
| Ever notice how on modern boats, the boom is not just so shorter section
| of the same type extrusion as the mast? There are engineering reasons
| for that (plus it looks cool).

Quit toying with the damn boom.... look think of it this way... how many
lifting devices utilize a support located under the boom at less than 25% of
the boom length? NONE!
Now how many utilize a cable [topping lift] to the end of the boom?? MOST!

You are dead wrong on this Doug... really!

CM

DSK wrote:
And the compression on the mast is likely to
be a multiple of the weight involved.

Oh boy! I though you said you knew some engineering. The vertical force
is _exactly_ the weight of the lifted object Doug.

Cheers