How did you come up with the shape?
Ian McChesney: Well, the brief was pretty prescriptive. They wanted a rotating shelter, driven by a vane pointing into the prevailing wind, in order to provide constant protection from the elements. On the train back from Blackpool, I literally tore off a bit of paper and thought that surely, if it were just to twist, it would have the vane and the shelter. I made up hundreds of models, all of which were slightly different - it became a bit of an obsession.
Of course, I did that thing of trying out hundreds of other ideas, but I came back to my initial response.
Aran Chadwick: I think that Ian is one of those architects who has a very good intuitive understanding of structures.
The only re-nements to the original shape were due to the wind. We wanted to use a wind tunnel, but the client would not go for it because of the cost, so we did it ourselves. You can do this thing with a fan, and if you have got a bit of string and a pencil in your hand you can see if it works. We tried a lot of different shapes with this very simple method. In the end, we came up with one which we suggested for the prototype.
Ian McChesney: We couldn't use any compound geometry.
There are boatbuilders who can do that sort of thing, but it was out of our price range. In any case, we were worried that it would look a bit too fussy.
Aran Chadwick: It's actually quite simple. There is a central spine, an axis of symmetry up the middle, so you can set up perpendicular sections and cut each one. Above the base plate, the structure has a skin and below it the fins just extend down and then cantilever out to pick up the bench.
How quickly does the structure rotate?
Ian McChesney: At the design stage, we just put a paper model in a bowl of water and stuck it down with Blu-tack, then blew on it with a hairdryer to test whether the thing would work.
Aran Chadwick: Later on, we were electronically logging wind speed, wind direction and the speed at which the turntable rotated. We were worried about it moving too sharply and people falling off, so we fitted a damper underneath to stop it turning too fast; a drum of oil with a paddle that moves about inside. The more oil you pour in, the more resistance you get.
Ian McChesney: We have ended up with a speed limit of a 250mm/secat wind speed of up to 20 miles per hour, with a very gradual increase at higher wind speeds. It just sort of nudges around.