Non-Congruent alternate interior angles

This sailboat has a pair of interior angles that aren't congruent. For two angles to be interior angles and to not be congruent they must be on two different lines that aren't parallel, and are cut by a tansversal. the sum of the angle measures also can't equal one another. This sailboat has a mast, boom and sprit  poles (which hold up the sail) all of these combine to form non congruent alternate interior angles. The top sprit pole (colored green)and bottom boom (colored red) are not parallel and the mast (colored blue) cuts through both of these up and down as a transversal. The angles on the interior of the boom and sprit pole that alternate across the mast aren't equal. As you can tell angle 1 and angle 2 are not congruent, they are alternate interior angles. A mast, boom and sprit pole are needed to make a small dinghy sail.  Larger sailboats need just a mast and boom, but some are designed to use sprit poles as well.  Professional sailors, collegiate sailors, club sailors, sailboat designors all use mast, boom and sprit poles in the sport of sailing.

This image can be found on: http://intheboatshed.net/2007/06/03/jims-canoe-gets-new-sails/