Thanks for the help!
As I'm not able to access the house today ( flying back home to Boston from St Thomas)..... I'm really thinking that I'll be needing the 21" version.... here's my theory.... the arms are about 8 1/2" from pivot to pivot.... now, there is that 4-5" section that bridges the window where it attaches to window, Soooo.....16-17 plus the 4-5" would make it around 21 or so.... think so?..... thanks VERY much.... these things don?t last a long time as it is about 1/8 of a mile from the water!
Best regards,
Corbin