[Imp]

All I can think of is the unit class is not recognised by the op filter.
Try changing the unit class, other option is adjusting the unit so its unarmoured.
Maybe try buying a variety of water craft from different OOBs & set up a test.
If you find one that is targeted as you want just modify the unit or look at its unit class & change the rigid raider to that.
Last resort you could try making it a amphib tank or hovercraft class with land speed of 1 (0 if lets you) Land speed of one would let you drag it to waters edge