The Sydney to Hobart yacht race has suffered a double tragedy after two sailors died in separate incidents. New South Wales Police say a crew member of one Sydney to Hobart entry was struck by a sail boom just before midnight.

Crews of more than 100 yachts set sail Thursday on a "boat-breaking" Sydney-Hobart yacht race, with gale-force winds and high seas forecast for the gruelling bluewater classic.

One sailor each on Flying Fish Arctos and Bowline were killed after being struck by the boom, a large horizontal pole at the bottom of the sail.

Favourite Master Lock Comanche has been forced to retire from the Sydney to Hobart yacht race, leaving LawConnect out in front.

LawConnect, which won line honours last year, was first past the turning mark in Australia’s premier yachting event but ran into sail issues.

Silas Nolan is another professional with a foredeck specialty and a résumé that covers racing worldwide. He worked his way up from small boats to the glory wagons, then sailed enough Hobart races to “almost get sick of it” and turn his sights elsewhere.

There have been plenty of “firsts” in the history of the Sydney to Hobart yacht race which was first held in 1945.

LawConnect was first out of the Heads, but a furling issue allowed line honours rival Comanche to grab the lead, while last year’s overall winner, Alive, was forced to retire just three hours into the race.