* h {\displaystyle h} is the sack.
In geometry, the distance between the middle point of the bow and the middle point of the rope below, or the height of the circular segment, is said to be a sail or arrow or a circumference of a circular arc.
The sack can be calculated with the expression: h = R ⋅ ( 1 & # x2212; cos ( θ 2 ) ) = R & # x2212; R 2 & # x2212; c 2 4 {\displaystyle h=R\cdot \left(1-\cos \left({\frac {\theta }{2}}\right)\right)=R-{\sqrt {R^{2}-{c^{2} \over 4}}}} .
wiki
