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