I know....I know.....whoda thunk 18" would be a problem.....

But...for that extra 6" you get.
Better horizontal resolution 5 Deg vs 7.5 Deg.
2 KW vs 1.5 KW peak power
NEMA inputs which will give a lollypop on your way points if
tie in your GPS. That alone makes it a lot easier to sort out
returns when you are busy.

The weight seems to be the same... about .5 kg...The mount probably weighs more..

It would seem from all the replies that very few have attempted to install radar on our beloved vessels