Francis Joyon, the French yachtsman, has looked to be on course to smash Dame Ellen MacArthur’s 71-day nonstop solo round-the-world record for weeks. But this weekend what had seemed straightforward suddenly turned serious as Joyon’s boat suffered rigging damage that could cripple his yacht and ruin his chances.

The gentle giant from Brittany has enjoyed an almost perfect run since setting sail from Ushant 50 days ago. Joyon has had superb weather and his 97ft beast of a boat – the blood-red trimaran IDEC II – has romped along at breathtaking speed, breaking all MacArthur’s records.

Then, on Friday, Joyon got a shock and found himself having to climb and then reclimb his enormous mast as his boat thrashed around beneath him. This came after he discovered that one of the main rigging wires or “shrouds” holding up the rig had worked loose and was about to come off. Should it have done, the 105ft carbon-fibre mast, effectively the boat’s engine, would have come crashing down and with it Joyon’s dream of recapturing the record he held before MacArthur beat him in February 2005 in her 75ft trimaran B&Q.

The drama for Joyon began just after the Frenchman recrossed the Equator on his 48th day at sea as he headed north in the Atlantic, at which point he was 12 days ahead of MacArthur’s equivalent position. The first problem was that the rope holding up IDEC II’s mainsail broke, requiring her skipper to scale the mast to replace it. It was while he was up the rig that he was alarmed to find that the starboard shroud had worked loose and was about to come off.

After what his shore team described as a “hellish night” for Joyon as he tackled squalls and difficult seas, he made two dangerous mast climbs on Friday and then a third on Saturday, sustaining heavy blows to his body and injuring his ankle in the process.

Like all great solo sailors, Joyon is a tough and resourceful character but even he has struggled to find a solution to the wayward fitting swinging around in the air so high above him, especially as he does not have the right tools to make a proper repair. He has managed only a temporary fix using ropes and is praying it will hold out for the remainder of his voyage.

Joyon’s trials at the Equator are similar to those endured by MacArthur, who was forced to climb B&Q’s rig twice about 1,600 miles south of Joyon’s position to repair damage to the boat’s mast track, that holds the sail against the rig. For the first time, her French rival is having to proceed with caution and at least one more dangerous climb is still required with Joyon planning to try to strap the shroud to the mast to limit the stress on it.

“I’ll be trying to find the compromise between risk and performance,” Joyon said as IDEC II sailed north in 20 knots of easterly wind. “I should be experiencing these conditions for three or four days, then it will be time to take the crucial decision about changing tack to get around the Azores high [meteorological feature] and pick up the westerlies.”

Jean-Yves Bernot, Joyon’s weather guru who speaks to the Frenchman every day on a satellite phone to discuss his routing choices, says the damage will slow IDEC II’s progress.

“I’m now working on the basis of 75 per cent of the boat’s theoretical polars [optimum speed],” he said. “ IDEC is sailing at 14 knots upwind, while she should be doing 18. The good news is that strong winds are forecast right up to the finish and Francis won’t need to hoist all his sail . . . the only unknown factor is the boat’s behaviour with the wind astern, considering the damage.”

Hopefully for Joyon he will make it, though probably not by next weekend as he had hoped. However, after what is already being seen as one of the greatest solo voyages of all time, he is still on course to take more than ten days off MacArthur’s time.