Hello Robert,

Whether it will be successful, depends heavily on the path profile
between you and the harbor. When there is a (small) hill between you
and the harbor, you will probably not get reliable reception, even
with a moderate sized directional antenna. Also increasing the height
(to practical values) does not have a large effect (when there are
hills in between).

When the profile is flat (as in most parts of the Netherlands where I
live) it must be possible. However when there are many obstacles
(buildings) close to you (in the direction of the harbor), you also
might increase the height of the antenna (be aware of higher risk of
lightning strikes).

I do not know the "scantenna", maybe some other people can tell us
that. When it is really good, you need a directional antenna to get
improvement. If you want to experiment with antennas, try to arrange
with the vendor that you can bring it back as it doesn't work.
Unfortunately, there is a physical relation between gain of antennas
and size: the more gain, the bigger the antenna.

Other issues
What about the noise floor and interference? Where I live, you cannot
use most scanners without a selective input filter when raising the
antenna.

With respect to using one cable for 2 antennas, yes, theoretically it
can be done, but I don't know whether there are good splitters/filters
in the market for your application.

Best regards,

Wim
PA3DJS
www.tetech.nl