Sure they can be used with a bit of a bend in them! Put the long vertical leg with the crown toward the davit arm, and when you load up the davit that crown will magically disappear. If not appear on the other side.
I've been watching this College Calculus & Engineering gab-fest wondering why nobody has suggested a KISS solution - hang a small chunk of I-beam off the porch beams and rafters, sticking two or three feet out over the loading area. Possibly with a couple of added support legs to concrete footings for insurance, or upgrade the area by adding another post and footing that matches the existing porch construction. And you can make a hidden gate in the railing so the loads don't have to go as high.
Use the same hoist for the load but mounted on a roller beam trolley. Convert the overhanging and swinging loads of that davit arm system to purely vertical loads of making sure the hoist beam stays up.
And don't forget a couple of rubber bump stops at the ends for trolley travel stops, impact loads can cause failure.
A proper use of a davit arm crane is outside where there isn't any other structure available, and they normally aren't designed for a support at the top of the post - you transfer all the loads down through a healthy vertical member to a large footing. You have a very handy house sitting there - use it.
If you take down the trolley and hoist, all that's visible is the beam. Ultra Slickness would extend the hoist beam across the porch to the house wall, and you make a convenient little closet that the hoist rolls into, with room below for storing the slings straps and spreader bars. You close a little door and "Presto!" it all disappears.
KISS!
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