Ok, now what makes you think this is a boat group??? Please refrain
from posting boat related stuff in here!

Ok, seriously ... what matters with VHF is antenna height and having it
properly tuned....

I also have a 4 foot antenna and in an emergency IF you have the time I
can unscrew it and hold it higher or duct tape it to a paddle and hold
that high up.

The same you can keep an 8 ft antenna and use that for emergencies

Both isnt ideal and only for non time critical emergency.

The other thing you have to ask yourself is how far you wil be away
from the shore? If not too far then 4 ft may be just fine.

Matt