Charlie,
My main VHF antenna is not mounted on the arch. I hesitated posting this reply, because the antenna I have is expensive and hard to get. It is a Celwave 19' antenna, mounted on the starboard side of the flybridge. The base is screwed into the side you access from inside the head. I have talked to people in Two Harbors (Catalina) on my night runs down to the dumper and lower 500. This antenna works so good, when the Customs boat broke it, I cut up some old outriggers and fiberglassed it back together.
My secondary Icom is in the galley and the antenna is mounted on the arch. It sucks too.
Here is the pdf (web link) to the antenna I have on my primary flybridge Icom.
http://www.marconi-marine.com/produc...ave/pdf/04.pdf
Glenn (Wizard)
"The Reel One"
26' Billfisher