The 70th Sydney to Hobart yacht race got underway on Boxing Day, with a massive 117 yachts in contention for the title in the classic ocean race. With no fewer than 13 helicopters over the harbour, Comanche and defending champion Wild Oats XI were followed by Ragamuffin and Perpetual Loyal as they sped from the Nielsen Park starting line.

Pushing into the Tasman Sea, the fast-moving fleet churned waters, with hundreds of spectator vessels of all sizes and classes along for the ride, shadowing as best they could the ferocious supermaxi yachts. But sunshine gave little clue of what lies ahead for the armada, with lumpy waters and winds upwards of 30 knots forecast for Friday night.

Although this year's may be a race for purists and those who have been yearning for a challenger to take on the seemingly unstoppable Wild Oats XI, it was a family affair on the tip of South Head, where hundreds looked out to sea, binoculars held to noses and picnics spread on rugs.

Val De Gica, who had pole position as she watched the boats pass through the heads, was joined by five friends for the spectacle. She said her love of sailing was one of the reasons she moved to Australia from native Argentina.

"It's amazing, I've never seen so many boats together. I've always wanted to do it, we've been planning this for a while," the 32-year-old said.

The visual merchandiser from Kensington said crew tactics were clear to see as those contending for line honours rounded the head.

"It's incredible, you know they are sailing on the edge. We could see Comanche's rudder," she said.

Sydney to Hobart newcomers Lars and Vera Goldstein, who moved to Sydney from Germany, watched with their children from Shark Beach.

"We're not really into sailing, we did it because everyone went," said the architect. "But it was great to see, and in the end I was surprised, I got excited."

An hour into the race and grey skies signalled the arrival of a brisk southerly, whipping the ocean into white caps. While families moved out of Camp Cove, ice-creams in hand, the winds would have been another story for the racing crews.

Telusa Veainu, a professional rugby player from New Zealand who plays for the Melbourne Rebels, watched the start of the race for the first time, looking down from South Head.

"All we hear about back home is the America's Cup. It's impressive to see these boats in real life, you realise how spectacular they are," the 24-year-old said.

As for a go at grinding alongside the crew of Comanche, the union player is happy on land, for the time being.

"I would love to, but it looks like a lot of hard work."