"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