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