Draft:Bpow46

This problem was suggested by Bill Evans. Thanks, Bill.

The captain of a luxury cruise ship wants to install windshield wipers on the portholes of the ship. The straight wipers are to be attached at a point on the circumference of the circular portholes, furthermore, the entire length of the blade must remain in contact with the flat glass at all times. How long should the wiper blade be so as to clean half of the porthole?

For the more adventurous: What is the optimal design for the blade; that is, what is the largest surface area of porthole which can be cleaned?

Problem by Alberto L Delgado, from the now extinct Bradley Problem of the Week.