What is a keel block and how is it used?

Yes, a docking block, they are put in a form and at heights so the bottom of the ship in a dock is supported on its structure, but also is supported over the length of the ship, otherwise the ship could break. They are put in place and as the water level lowers in the drydock divers see if they are in place and adjust with extra wood to fill up gaps if necessary.

Thanks for the invitation.

I agree with answer of Mr. Jetley.

A docking block used to support a ship's keel.