What are "mid-ship hoops"?

Midships (that's the proper term) simply means in the middle--not at the front, not at the back, but in the middle.

Now, this is going to take two images because they just don't make river boats like that any more. This is an image of a river boat with a canopy:



But that canopy is not supported by hoops. The hoops referred to look the ones in this image of a 19th century wagon:



So, imagine that boat, with a canopy supported by hoops like this.

If this is Burmese Days again, Orwell is showing that he's not much of a nautical person. There is a term, midship, but it is not commonly used, and almost certainly not by sailors. I didn't find it with a hyphen, but even if you did, that's not what a sailor would say. There is a noun, midships, meaning the middle of a boat or ship; and there is an adverb, amidships, meaning the same thing. Midships can also be used as an adjective. but it is uncommon.

Midships as a noun:

The waisters are the unskilled crewmen who congregate in the midships, ready to haul on a rope or to push the capstan bars, as they're ordered.

Amidships as an adverb:

They're called waisters because waist is another term for the area of the deck located amidships.