Thank you to everyone. This project is only temporary. I'm building a new floating dock on top of my old dock. I just need to raise and slide it ever so gently into the water. You know what they say. It only costs a little bit more to do it yourself.
I need to erect a hoist beam with a 10' span using square tubing. Which is stronger, 3"x3" 1/4" wall or 4"x4" x 3/16"? Also, how much weight could I lift at the center?