What's this called ?

Pete1970

It attaches to the top of shelf in aft cabin to ceiling, I bought a used boat and could only find one but I require two.

NavyCTRC

In the boating world things sometimes have names according to what they do, that is why we have three names for rope.  Line, rope and rode.  It looks like a stanchion, but without a further description of what it is doing exactly, can't help.

aero3113

It looks like it's an expandable cloths hangar?