What is it with German carmakers and four-door cabriolets? Our discovery of patent drawings for a topless Porsche Panamera is the latest in a series of wild proposals that started with the very limited run Maybach Landaulet.

In 2007 Mercedes revealed the Ocean Drive, a true four-seater convertible with a folding fabric roof. The global crunch probably but paid to that S-class based idea, but there are also rumors around that Audi would like to do something similar on its upcoming A7 big four-door fastback.

Aside from a signs of a weird fascination with classic four-seat, four-door convertibles such as the 1960s Lincoln Continental, the German carmakers seemed to be doing nothing more useful than making life very difficult for their engineers.

Trying to make a respectably stiff car out of a structure with no roof pillars and two door apertures on each side must be close to impossible. A secondary bulkhead directly behind the front seats has to be a possibility.

And then imagine designing a roof long enough to stretch from boot to windscreen that’s also neat enough to be bundled up without robbing all the boot space.

It’s no surprise that the Maybach retained its roof cant rails and rear roof pillars and had a secondary bulkhead in an attempt to retain some semblance of rigidity.

The engineering challenges involved in converting the Porsche will be complex and expensive. And is what would inevitably be labeled a Monaco cruiser really be a suitable addition to the Porsche stable?