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.