Answer:
The equilateral triangle sail has the greatest area.
Explanation:
The area of a triangle is defined by

Where
is the base and
is the height of the triangle.
Notice that we have a scalene triangle, an isosceles triangle and an equilateral triangle.
Scalene triangle area.

Isosceles triangle area.

Equilateral triangle area.

Therefore, the equilateral triangle sail has the greatest area.