Apologies Nerys. For the first time in 50 years I have just had to steam the middle of a plank!
I am currently building a live steam tugboat which has a curved strake running round the stern. An obvious candidate for bending from the centre.
I used part of that previously cursed plastic tube with an end cap forced on, rather than glued. I stood this up in a jug to catch the leaks this time! Filled with boiling water, dropped in the plank and placed a piece of tape over the top to stop the plank floating out. After 5 minutes most of the 400mm plank was extremely flexible.