Gilles
I saw a ketch in Port Vila which had the AirMarine ontop the Mizzen.

I (and two copied me) chose to mount mine roughly half way up the
mizzen because of cable length/losses on a bracket I designed.

It looks a bit like the left hand side of the capital H with the right
hand
vertical the mizzen and the left leg bent towards the mizzen. The
mountings
are shaped to the profile of the mizzen.

In this position it works very well, cable losses are at a minimum and
more important there is no vibration transmitted down the mizzen into
the aft cabin. My iAir is probably 5/6 years old (the version which
gives
a thump when changing speed). Even the thump is barely noticable.

The proof in the pudding as they used to say is that others have copied
it
with similar reactions.

I placed pieces of tractor tube between the two mounts to give added
anti vibration effect but as the mounts themselves are pop-rivetted to
the mizzen, I wonder if this works.

lozza