Ya, so that boat has radar limiting design elements. This is a typical radar reflector. With 2 surfaces at right angles, the radar signal will be reflected back at the detector, pretty much ensuring detection. You can see this boat has no right angles in the planes where a signal would reflect. Really oblique signal paths won't reflect off the second surface, so the beltline of the boat shouldn't be an issue. If you imagine radar signals hitting this thing, they just won't hit anything big enough to bounce directly back at the radar emitter. Which I'm sure they tested and optimized for.