Well, you've got quite a challenge there.

Mike Halloran
Pembroke Pines, FL, USA

The picture isn't quite clear to me.  Why would it need to store smaller in both dimensions?

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Rust never sleeps
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available space to retract into is 200mm x 100mm x 1300mm
sorry for the confusion. there is also more space available 100mm back from pool face but is only 75mm high x 350mm deep x 1300mm wide.
how feasible is a stainless hinged shutter system that could fold over and fit into the space mentioned and be strong enough bearing in mind total submersion.

Something like a metal tambour door might work.  It would need tracks on the edges adjacent the storage pocket.  It would have to be relatively thin to roll up in the proposed space.  The thinness would make it flexible, so even if it were strong enough, it might create a perception of weakness, and frighten the users.

Or, you could put in a rigid 1000 x 1300 mm deck, and fold it down into the pool when the pool is in use.  It would require a sturdy hinge/drive mechanism that might fit into the available space, or not.  Again, there might be perception problems that would force use of latches at the distal end.

Did you have something else in mind?

Mike Halloran
Pembroke Pines, FL, USA

Aside from the above mentioned trambore approach here are some different approaches using grills. Another approach might be to use the folding partition panel approach. Some of these stack at at an angle instead of an accordian fold for thin partitions.  

http://www.dynamicclosures.com/

http://accordion-door.com/rolling-grilles-closures.html

Here is another approach. This is just one of many forms of shutter. They may be available in SS.

http://www.stormshutters.com/accordion-shutters/accordion-shutters.html