After all this hullabaloo, I will mention that I am a retired
registered professional engineer. I try to make constructive comments,
but will not attempt to suggest any design when all the facts are not
given.
If the loading is 200#, there are many models of pickup cranes
available that are guaranteed for 1/2 ton or more. Buy one of them.
If you want to use the material you bought, I would suggest an open web
steel joist construction to fit the dimensions of your ?boat? plain
tubing will deflect just as discussed.

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Well, you get the general idea. Properly designed & executed, the joist
structure would pick up a Volkswagen. Look at a commercial construction
crane for inspiration.
Bugs