let

h = the height of the sail, h>= 0

a = the length of the base of the sail, a>= 0

A = 60 ft^2 the area of the sail

the height of a triangular sail is 1 ft less than twice the base of the sail

h = 2a - 1

the are of the triangular sale is A = (1/2)a*h

(1/2)a*h = 60

plug h = 2a - 1 into the last equation

(1/2)a*(2a - 1) = 60

by solving we find

a = 8 ft

click here to see the step by step solution of the equation

h = 2*8 - 1

h = 15 ft

the height and the length of the base are 15 ft and 8 ft.