I'm going to assume you start your radar and adjust it at either 3 or
6 mile range, and when you see these arced targets, they are generally
larger, at relatively close range, or when you are on a lower range.
If so, first step, try increasing sea and/or rain clutter. If this
doesn't get rid of them, retune the set for lower ranges (that you may
be on) and reduce gain and/or intensity .... slightly.
As always, try to stay on the higher ranges ... Id only use 0.75 down,
for docking or running inside a marina (personal experience/choice), for
example, Oak Bluffs, Hyannis inner harbor, Boston Harbor marina.

otn

Jeff Morris wrote:
An interesting explanation, but this isn't the image I see. They appear from
medium sized vessels (tugs, CG, etc). They are roughly a 90 degree arc of a
circle centered on my vessel, and intersecting the target. Thus, the radius
indicates range, and the position of the arc is the approximate direction.
Although I always assumed it was something "active" on the target, I'm beginning
to think it might be entirely my radar. The fact that the arc is on both sides
of the target makes me think that my transmitter is radiating small side lobes
(if that's the correct term) that precede and follow the main beam. If the
target is a large reflector, and my gain is high, that might show as the arc.

-jeff