Sloops, ketches, and yawls have triangular-shaped sails.
Square sails (rectangular) were (are) called four-cornered sails.
Trapezoidal, actually. But the square sails were called square sails. Lateen or square could be referred to as yards.
"Square-riggers" have primarily square sails, but the jib sails are triangular.
The rudder was used to steer left or right, along with the sails.
Square sails are square
They were referred to as "four-cornered" sails.
because if the sails didn't work you would still have the rudder in the back and you would have to control it another way
Square sails are not truly square but rectangular with a longer long side on the bottom perimeter of the sail. They were and are referred to as "four-cornered" sails.
The boat had triangular sails.
foremost sail has triangular shape
One type is the "lateen sail", but there are also jibs; Genoa & spinnaker.