rickman wrote:
I don't think this design would be a great choice for a kayak antenna,
because the individual coax sections in the "stack" are a
half-wavelength long (at the coax's velocity factor) and there are
usually quarter-wave sections at the top and bottom. The shortest
2-meter collinear (one half-wave section and two quarter-wave) would
be 2 meters in length - over six feet - and a marine VHF antenna
wouldn't be much shorter.

With a collinear of the type shown in the above link, you'd need to
mast-mount it up some distance - the bottom quarter-wave tube is
RF-hot, and if its bottom end is near water (or anything grounded) it
would tend to de-tune the antenna.

As others have noted, the OP really doesn't need a high-gain antenna.

I think the real problem is this antenna for 2 meter operation is 20
feet long! For marine VHF it can't be used on shore, so hanging it from
a tree would not work. When you say using a single half wave section
wouldn't be much different from a marine VHF antenna, what type of
antenna would a marine VHF antenna be? I thought they used a colinear
design.

I wonder, why is the "2 meter band" not called the "6 1/2 feet band"
in the USA? This alternating between meters and feet is getting a
bit funny.