Buildin Hydraulic Lift for Pool.

Hello All,

I would like to make a hydraulic pool lift that can uplift the seat to the 6 feets from ground and then slide the seat towards the pool (roughly 2 feets on lforward direction) and then put the seat down gradually inside the water.
Pool is 4 feet deeper and 15 feet in diameter.

I want to make this for my grandfather.
Please help me to provide some ideas. Thank you so much.