There are several ways to get the radar or even radars revolving.
I myself modify mini servos to run constantly (1.5volts) then if I need two radars I fix drive wheels to shafts and have an elastic band between them.
There are very small motors on sale (I think if you contact 1 Mr FLJ) he may steer you in the right direction for those
Then there has been use of a "toy" disco light thing stripped down for the drive system.
So as you can see the possibilities are almost endless, the big question is where on your vessel do you want the radar because that will influence the type of drive
R.