The Frenchman was taking part in the Vendee Globe race when he hit an object believed to be a shipping container on Sunday night.
"The shock was exceptionally violent. It gives me the shivers just thinking about it," Ruyant said in a message posted on the race's website. "I was at 17-18 knots and came to a sudden standstill... the whole of the forward section exploded and folded up."
At the time, he was about 150 nautical miles (280 kilometres) off New Zealand's South Island.
With his yacht in danger of splitting in two, Ruyant stowed his sail and began slowly motoring towards land.
"I'm in helicopter range, which is reassuring," he said. "I just have to push a button and they'll come and get me. The inside hasn't been affected and with my watertight doors, I'm sheltered."
Maritime New Zealand rescue coordinator Mike Roberts told the AFP news agency the sailor was expected to make landfall late Tuesday but bad weather was closing in.
Meanwhile France's Armel Le Cléac'h cemented his lead from Alex Thomson in the solo round-the-world race, leading by 512.2 miles on Monday.
Behind that duo, Paul Meilhat of France was third from compatriot Jeremy Beyou.
The race embarked from western France on November 6 with the winner expected back on France's Atlantic coast by January 20.