It happened on the B3081 near Verwood - he had to be cut free by firefighters.
Tributes At Olympic Sailor's Funeral
Sir Ben Ainslie has paid a poignant tribute to Olympic sailing gold medallist Andrew "Bart'' Simpson today.
The four-time Olympic sailing champion spoke outside Sherborne Abbey ahead of Simpson's funeral, and described the father-of-two as "a friend to us all''.
Hundreds of mourners - family, friends and fellow sporting champions - attended the service in Simpson's home town of Sherborne in Dorset.
Sir Ben, a long-term friend, said:
"We are all devastated by Andrew's loss and it has been a very difficult period for all of us as we come to terms with his passing.
"Andrew was a devoted husband, adored father of Freddie and Hamish, son, brother and friend to so many of us.
"The fact that so many people have come here from all over the world speaks volumes of the kind of person Bart was.
"Whether Andrew met a young kid learning to sail or a four time America's Cup winner, everyone loved Bart because of the person he was.
"He always had a smile on his face and that is the way we will always remember him.
"One of the things Andrew was truly passionate about was helping young sailors get into the sport and for that reason we are looking at setting up a charity in the near future in Bart's memory.
"Leah especially sees the day as a way to celebrate Andrew's life and to remember Andrew as we all knew him.
"In many ways Bart was understated in life, this is really the occasion to celebrate his life and to remember what a huge impact he has had on us all.
"This is a fitting tribute to the person who gave so much.''
Sir Ben was a pallbearer at the funeral, along with sailing greats Nick Harrison, Chris Brittle, Paul Goodison MBE and Anthony Nossiter.
Winchester's Iain Percy OBE, Simpson's sailing partner, best friend and best man at his wedding, also carried his coffin.
Sherborne, where Simpson, 36, lived with wife Leah and their two young sons, has been dressed with red, white and blue bunting in honour of its sporting hero.
Simpson, respected at home and abroad as a talented but fierce competitor, was killed while training for the America's Cup in San Francisco Bay on May 9.
He died after being trapped under his super fast AC72 catamaran when it nosedived, capsized and broke into pieces while training with Artemis Racing.
The father-of-two won gold alongside Percy at the Beijing 2008 Games and silver at the London 2012 Olympics in the Star discipline.
Percy gave an emotional tribute to his best friend and sailing partner at the funeral. He spoke after readings by Miles Bradbury, James Donaldson and Sir Ben and a chant of Coldplay's Fix You.
Percy tearfully told the hundreds of mourners Simpson ``spent his life giving to others''.
He said: ``This is going to sound like a bit of an explanation. Everything sounds fantastical about Andrew, bigger, brighter.
``But all of us that experienced him the most will know that it is all true.
``In fact, no words will ever do him justice. He was more loved and in love, more jolly and outspoken, more kind and generous and compassionate.
``Andrew was not normal, he was special in so many ways. He was an example to all of us that met him and for the next generation too.''
Percy said Simpson did not ``shout about his greatness'' but was determined and dedicated.
``I know no man who was loved more than Bart,'' he said.
Simpson loved sailing but would always make time for his parents and sister - and wife Leah, he added.
``Andrew never looked back, he fell in love with Leah more completely than I have even seen. He was always a fun, happy person but over his time with Leah he became complete.''
Percy tearfully told mourners how much he missed his best friend.
``I have to say I have never needed Bart's guidance so much,'' he said.
``He was the man I always turned to for friendship and advice and I miss that terribly.''
Before the emotional tribute, Sir Ben read Bishop Brent's What is dying?
Mr Donaldson read The Book by Paul Meadows, while Mr Bradbury gave an extract of 1 Corinthians. Hymns were sung and One Day Like This by Elbow was performed, before prayers.
The mourners stood to sing the final hymn, Jerusalem.
Final prayers and blessings were read by The Right Reverend Dr Graham Kings, Bishop of Sherborne.
An arrangement of Sailing by Gavin Sutherland was performed as the coffin left the Abbey.
Crowds who had lined the streets of Sherborne as Simpson's cortege was brought through to the Abbey listened to the service outside through loudspeakers.
They watched as the distinguished pallbearers carried Simpson's Union flag draped coffin out of the service.
Leah Simpson, mother to their two boys Hamish and Freddie, released a tribute to her ``loving husband'' after the service.
In a statement, Mrs Simpson said: ``Andrew was a wonderful person. He was a loving husband and a devoted father to our two boys.
``I am so pleased that so many of his friends and family are here today to celebrate his life and achievements.
``He will be forever in our thoughts and hearts.''
Speaking to the Press Association before the service, Simpson's sister Amanda said he was her "inspiration for 33 years''.
"As many people have told me in the last few weeks Andy has accomplished more in his 36 years than most people do in their lifetime.
"We have been deeply moved by all the beautiful tributes received during this immensely sad time.
"When we were young I annoyed him as all younger siblings do, but as we matured our relationship changed. He would look out for me at sailing events and would always be there to help pull my boat up the beach and we would discuss tactics.
"I look forward to teaching both Freddie and Hamish how to sail so they can also share in our passion for sailing.
"Andrew's presence will be greatly missed by our whole family and we look forward to setting up the charity to carry on inspiring grassroots sailing in Andrew's memory.''
Following a private burial, there was a celebration of Simpson's life at Sherborne Castle.
Mourners were asked to bring photographs of Simpson which will be used to create a memory wall.
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