The rig is a liftable boat with accomodations for platform operators
<a href="//www.flickr.com/people/46383895@N00" class="extiw" title="flickruser:46383895@N00">Enrico Strocchi</a>
CC BY-SA 2.0
<a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a>: <a rel="nofollow" class="external text" href="https://www.flickr.com/photos/46383895@N00/1350903785">Rig</a>