what is it?

[Schakel]

Upside-Down cake?

The material before shaping it to a surf board.

 

[G. Brandt]

:lol:  No, it´s not a cake, not even the sculpture in the movie A Clockwork Orange and not the yellow canoe.  
Sorry to be boring, it´s only the bottom of a 3D printed hull maybe the biggest 3D print of a sail boat ever done so far, with a concave hull.
We have now started to built the sail boat in full scale and it will hopfully be sailed into a lake during the spring 2020.