Parkinson dived into the water and under the yacht to help the woman. However, the force of the tide meant she was trapped by her lifejacket on the prop shaft of the yacht's propeller.
He managed to get her head just above the water.
"I knew if I let go of her she would be straight back under - she was losing consciousness as well."
Cdr Parkinson directed the other member of the couple's crew to call an ambulance and get him a knife. He went under again and managed to cut away some of the lifejacket.
Then, using ropes from the yacht he secured the woman, so she wouldn’t sink or get carried off in the fierce current.
Parkinson feared the ambulance would not arrive soon enough.
"The colour had gone from her face. Her lips had turned blue. She was obviously not in a good way at all."
Paramedics spent 10 minutes stabilising the woman before transferring her to hospital. One of the South Central Ambulance Service team, William Pammenter, was in no doubt that Parkinson's actions had saved her life.
"I believe that Andrew made the utmost difference to Linda that day and without him being there the situation would have been very different."