It soon became clear his estimates for the boat’s speed had been wildly optimistic: He had estimated an average of 220 miles per day, whereas the reality was about half that, on a good day. There was no way he was going to catch up with the other competitors or win either of the prizes, unless something extraordinary happened. 

And so, just five weeks after setting off from Teignmouth, Crowhurst started one of the most audacious frauds in sailing history: He started falsifying his position. Beginning December 5, he created a fake log book, with accurately plotted sun sights, working back from imaginary positions. To make it look convincing, he listened to forecasts for the relevant areas and wrote a fictional commentary as if he was experiencing those conditions. It was quite a feat of seamanship, and only someone of Crowhurst’s brilliance could have carried it off convincingly. 

Colin Firth stars in the The Mercy as solo sailor Donald Crowhurst.

After a few days’ practice, he felt sufficiently confident to send his first “fake” press release on December 10 claiming he had sailed 243 miles in 24 hours, a new world record for a singlehanded sailor. In fact, he had actually sailed 160 miles, a personal best perhaps, but certainly no world record. And so the great deception began. As Crowhurst slowly worked his way down the Atlantic, his imaginary avatar was already rounding the Cape of Good Hope and heading into the Indian Ocean. Gradually, partly through misunderstandings and partly due to the spin added by his agent back in the UK, Crowhurst’s positions became ever more exaggerated, until it looked like he might win the race after all.

Meanwhile, the real Crowhurst was pottering around the Atlantic, “hiding” in exactly the same area he had, only a few weeks earlier, jokingly suggested a sailor might hide to falsify a round-the-world voyage. To make sure his radio signals weren’t picked up by the wrong land stations, he maintained radio silence for nearly three months, from the middle of January until the beginning of April, which he blamed on his generator breaking down again. Unbelievably, he even put ashore in a remote bay near Buenos Aires in Argentina to buy materials to repair one of the hulls which had started to fall apart. Despite being greeted and logged by local officials, this rule-breaking stop remained undetected. On March 29, he reached his most southerly point, hovering a few miles off the Falklands, 8,000 miles from home, before starting his ascent up the Atlantic.

Finally, on April 9, he broke radio silence and exploded back into the race with a telegram containing the infamous line:  “HEADING DIGGER RAMREZ,” suggesting he was approaching Diego Ramirez, a small island southwest of Cape Horn when in reality, he was just off Buenos Aires. By this time, Moitessier had had his “moment of madness” and had dropped out of the race and sailing to Tahiti “to save his soul.”  The only other competitors left were Knox-Johnston, who was plodding slowly up the Atlantic and on track to be the first one home, and Tetley, racing in his wake to pick up the prize for the fastest voyage. It seems likely that Crowhurst was planning to finish a close second to Tetley, which would save him from financial ruin without drawing too much attention to his fraudulent log books.

But his reappearance in the race had a dramatic effect on the course of events. Already nursing a broken boat up the homeward leg of the Atlantic, Tetley worried he might lose the speed record to the resurgent Crowhurst, and started pushing his trimaran faster towards the finish line. Some 1,100 miles from home, the inevitable happened and Tetley’s boat broke up and sank, and he had to be rescued by a passing ship.