SteveB wrote:
Thanks for your input, Chris. This is going to be mounted at a corner, and
needs to swing in through the handrail, so a stiffleg is out because it
would hit the building.

I get a better idea what you need now. I'm sorry this thread has turned
into a flame war about mathematics with which none of use are entirely
familiar. It does muddy the waters.

I can see that a stiff leg is out of the question. Is your building
wooden, brick, stone or what? 200 lb is not an enormous load and I think
it might be possible to attach the davit to the building without the
long vertical column. If you do a Google image search for "wall crane"
and "wall hoist" you'll see pictures of cranes which are attached
directly to the structure of a building. Some of these are quite hefty.

As I suggested (but it got lost in the argument somewhere) I think the
weakest feature of your design is that the load will be attempting to
bend the vertical column. I'm not a structural engineer, but my
intuition is generally good and this is fairly clear I think. If you
took a long length of box section, clamped one end to the bed of a
pick-up and leant on the other end, it would deflect quite a bit. But if
you push on the end of the section, as if you were trying to push the
pick-up along, it would be much harder to buckle it. So basically you
could build something like one of those wall cranes, but have a column
below which carries compression only. I did a little ASCII sketch (turn
the fixed font on now):

-|\ -|\
| \ | \
| \ | \
-|---\ |---\
| |
| |
| -|
| |
| |
| |
| |
_|__________________________|_______
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

My preference is for the design on the left, as it avoids bending the
column. But I do think my original suggestion of an 8" deflection
without stand-offs is inaccurate. Given Ned's estimate, plus perhaps a
little extra flexibility in the mountings, 1" to 2" seems more
reasonable. But that's still a bit bouncy for my liking as flexing can
cause problems such as pivots jamming, etc.

I'd be interested to see pictures and drawings. Feel free to post them
online or e-mail them to the above address (remove NOSPAM). Good luck
and let us know how you get on.

Best wishes,

Chris