As competitors depart our shores today for the longest leg of the Volvo Ocean Race, Auckland firm Southern Spars says they've reaped more than $6 million so far from this year's event.

Southern Spars, which manufacture carbon fibre masts, booms and rigging, has enjoyed a long history with the Volvo and its predecessor the Whitbread and has equipped seven of the nine winners since 1989.

The company, which employs more than 300 staff, was selected as a supplier in the last two "one-design" races, where all boats are identical.

So far, the work for this year's race has been worth more than $6m to the company, says co-founder and sales director Mark Hauser.

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"We were picked as a mast supplier so from that point on we were heavily involved in the design of the boat and supplying the masts and rigging for all the boats, plus spares. And then we have a big invovlement in the servicing of the boats all the way around the world. Our guys are at each port," he said.

Hauser said the race had been a big part of Southern Spars growing its business and its marketing around the world.

"It's has been good us, long may it last," he said.

While suppliers were yet to be decided for future Volvo events, Hauser was hopeful Southern Spars would continue to be involved.

The boats depart Auckland today for what organisers call the "defining leg" of the race en route to Itajai.

The fleet will leave head south past New Zealand's East Cape into the Southern Ocean.

"There will be big waves and there will be big breeze. And icebergs," race officials say.

"This is the one that everyone wants to win. It has more myth and legend swirling around it than the Holy Grail."