27-year-old Ryan has penned a two-year deal at Huish Park after he left Cambridge United at the end of last season.
The 6’4” striker started his career at Burnham FC where he played nearly 300 games and scored 114 goals.
In 2013 then signed for Portsmouth where he made 20 appearances. Whilst at Portsmouth he spent time on loan at Havant & Waterlooville and Cambridge United.
After leaving Portsmouth in 2014 Ryan re-joined Cambridge United where he made 24 appearances scoring six goals. Towards the end of last season he joined Hartlepool United, where he played six games, scoring twice.
Manager Paul Sturrock said: “Ryan has come out of non-league at a relatively late age. If you look at his goals to games ratio that he has started it shows he has plenty to offer.
“I have watched him over the past few days during training and he certainly has goals in him. And goal scorers are invaluable at any football club.
“He is a big lad and will give us a great option up front. We are pleased with the signing and I hope Ryan pushes himself to be a starter in the team.”