Dave wrote:

a solid ground plane would be more efficient, but is of course bigger,
heavier, and more wind load if you are worried about it blowing around. the
3-4 radials bent down gives an easy way to fine tune the impedance... of
course if they aren't stiff enough they can get bent if slapped around in
waves.

Why would a solid ground plane be more efficient? What's the loss
mechanism in radials?

Roy Lewallen, W7EL