On Fri, 21 Apr 2017 00:28:47 -0400, rickman wrote:

Starting over from scratch...

A kayaking friend was asking me about antennas for marine VHF radios.

What problem is your friend trying to solve? My guess(tm) is that he
wants more range from what he's getting on his VHF marine handheld
radio. This is a common problem because the typical rubber ducky
helical antenna used on handheld radios has very low gain and is
lacking a proper counterpoise.

The first improvement would be to replace the rubber ducky antenna
with a 1/4 wave vertical stiff wire antenna on 156Mhz. It would be
about 48cm (18.9 in) long. That will provide a little gain and not be
too long and unwieldy. There are various such antenna available that
can be cut down to length. I would need to know the radio model and
RF connector type in order to be more specific.

Then next improvement would be a counterpoise ground element. In ham
radio circles, it's called a "tiger tail".
http://www.hamuniverse.com/htantennamod.html
https://www.google.com/search?q=tiger+tail+antenna&tbm=isch
It's just a length of 1/4 wave insulated wire dangling opposite the
antenna element. You could get fancy and use 3 or 4 such counterpoise
elements, but the improvement over a single element is minimal and not
worth the effort.

If the kayak was of a larger or ocean going variety, it might be
possible to mount a larger marine antenna like this:
http://www.n0lx.com/kayak.html
It's for HF, but would serve as a suitable mount for a VHF antenna.
A key component is the mount:
https://www.westmarine.com/antenna-mounts
I suggest something like this bolted to a backing plate:
https://www.westmarine.com/buy/west-marine--dual-axis-ratchet-mount-nylon--1986645?recordNum=12
The thread fits most larger marine antennas.
https://www.westmarine.com/vhf-antennas

Light reading:
"VHF Marine Antenna Fundamentals"
http://www.boat-project.com/tutorials/vhfant.htm

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558