bob smith wrote:
I want to install two posts to hang a hammock. For aesthetic reasons I dont
want to camber them away from one another as typically
suggested. What size steel tube would I need such that deflection is
basically non-existant with a typical 1-person weight on the hammock? (lets
say 200 lbs) The posts would be 6' above ground, 4' below ground. The
hammock would hang from the top of the posts.

I was thinking 3" diameter but I'm not sure if the minimum sidewall (1/8")
would be acceptable or if I should go thicker.

I think that would be marginal depending on how tight the hammock is strung.

What size would be equivalent to a 6x6 wood post for this application? (ie.
primarily bending strength)

Harold's suggestion of 3" sched 40 pipe should be ok but is not quite as
strong as a 6x6 post of good wood.

Note that E is a property of a material and is approx. 30E6 for any
steel. Formulae for I for various geometries are given in Machinery's
Handbook. For 3" sched 40 pipe, I=3 in^4 approx.

Note also that you don't have a simple cantilever beam. You have an
eccentricly loaded column carying both compression and bending.

Ted