Reference photo for sketch above https://proporzionedivina.wordpress.com/2003/09/26/ancient-chinese-sail-design-2000-years-old-and-still-going-strong-%E5%8F%A4%E8%80%81%E4%B8%AD%E5%9C%8B%E9%A2%A8%E5%B8%86%E8%A8%AD%E8%A8%88/