Tidey competed for Ireland at her first Games in Rio last summer alongside the now-retired Andrea Brewster, finishing 12th, and has now linked up with Great Britain's Charlotte Dobson to sail in the 49er FX event.
Tidey, 23, qualifies to race for Great Britain through her father, and admitted Brewster's retirement from the sport proved a decisive factor in her decision.
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"There wasn't an option here in Ireland in the 49er FX with another girl who had the experience to sail at the same level that I had finished up at [in Rio], to be competitive and win a medal in 2020," she said.
"I think that myself, along with Charlotte Dobson, gives us a strong combination going forward to achieve what we both individually want.
"It's not been easy personally for me. I'm so proud to be Irish, I will always be Irish, and I absolutely couldn't have been prouder to represent Ireland at Rio 2016.
"I'm grateful for what has happened, but now I am looking forward to four years of 100% focus on performance."
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