Close open poly surface

This hull was imported from MaxSURF as an open poly surface, I am having trouble closing it and editing it as an object. Any help?

3DGA.3dm (326.2 KB)

Hello - there is not enough there to close, unless you intend to add thickness to what is there - also,there is some noticeable messiness here:

I think I’d explode, Untrim and re-intersect, trim and join the surfaces.

-Pascal

I think I have followed your instructions so far, if I wanted to add a thickness to make the surface an object, how could I do so? This is my first project in RHINO so I may have made some mistakes.

3DGA.3dm (1.5 MB)

The project was an export from a different software, so certain edges are less than ideal for accuracy, unfortunately.