The idea is to extend the mast of the Spar above the deck, and then to hang a lightweight deck as a tensile structure, akin to a bridge, off the mast. This is a good idea because tensile structures are cheap compared to compression structures.

The cables would probably be fairly light, and number in the thousands, rather than having a few big cables – better to spread the support. The deck would probably have a few major masts extending NSEW to hold the deck in place horizontally, possibly also supporting tensioning cables.

This structure would be open decking, so waves would pass through it, and primarily be intended for low-value activities – rented housing, farming, solar energy collection. Things which are either not destroyed by a big wave, or can be cheaply rebuilt afterwards.

If one was expecting big weather, people would lash all loose objects to the deck, and then retreat to the mast until it was over. In an emergency, I suspect the deck could be jettisoned at a relatively low cost compared to the spar itself. Envisage things like lightweight construction practices.

Conventional spars were built for heavy equipment, not for maximum cheap surface area, so I suspect nobody ever had the need that would give rise to a design like this.