Hi Larry

Cant help you with a specific choice. Be aware though that considering
the boat thumps around in the water the antenna will never be always
quite vertical. If you run a "gain" device you may find you'll get a
more choppy signal and max radiation lobe that never quite line up with
the optimum. As an indicator a 5/8 (car mobile) whip in rolling country
can actually work worse than a 1/4 wave. (And also in a city/skyscraper
area, but for a different reason)

FWIW I do remember a 5/8 over 1/4 wave design some years ago where you
could remove the phasing section and above. A handy feature.

Of course if the boat motor is broken and there is no swell it may be
good to have gain!

Cheers Bob VK2YQA

Larry wrote:

I've thought about doing just that. A 1/4 wave on 2m is about 19" and
would not require folding down. I was kinda hoping to find some gain
which would also match the VHF Marine band antenna next to where it
would be, but I can't find anything so far.