There is a $4$m by $4$m square pond. You have $3$ straight planks of wood, each exactly $2$m in length.
You need to place the planks so that they go from one corner of the pond to the diagonally opposite one. There is to be no plank overlapping.
The planks must be laid rotationally symmetric around the centre of the pond.
How do you do it, using only a water-compass? (i.e. no angle-ommeters!)