‘Don’t worry about me!’ I called cheerfully as I inched along a long thin metal strut suspended high above the main deck of the boat. It stuck out over the sea like an enormous tuning fork lying on its side.

‘I’ll easily get back’, I added, just in case anyone doubted my balancing skills. I genuinely believed I could reach the other end, turn myself around, and work my way back again.

Then I looked down and saw just how far it was all the way down to the dark waves below. I froze. The only way I would ever move from here would be with the help of a coastguard helicopter rescue team.