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Run some test, and it look like there is no measurable difference in detection range, no mater what target ship RCS is (Nanuchka was able to detect Skjold at max range, the same was true for Nimitz...). Placing target with shore just behind doesn't seem to change anything.
Now, I don't claim what I knew that difference there should be, but why so many navies are investing in ships with reduced signatures if they don't change anything?

These are ship-to-ship detections, right? So your detection range is horizon-limited. At such short ranges the reduced RCS doesn't matter _much_.

Now bring up e.g. a P-3 at high altitude with its surface radar on, and you should notice the differences in detection ranges.

I tried a Tu-95 against a Sovremenny destroyer (detected at 174 nm), Visby corvette (142 nm) and small RHIB (101 nm).

I went and did a similar test with a P-3 against a Freedom LCS and a Type 21 frigate (similar displacements). I detected the Type 21 right at the edge of the P-3's radar range (199.7 NM). The LCS however, didn't show up until 94 NM. Given the P-3's sensor arc of about 240°, that reduction means you've reduced the P-3's effective search area by over 75%!

Well, it explains everything for horizon limited ship radar. But what about OTH ship radar? Nanuchka, from my OP, has one. It isn't horizon limited, and is detecting largest combatant afloat at the same distance as small corvette with RCS reducing features...

Save?

Sure. In B538 Nimitz is detected at 35 nm, Skjold at 34.9, or 35 nm. Haven't tested in different builds.

And to follow up another part of OP - does model allow for environment clutter? Can I expect that stationary (no MTI or Doppler help for detection), very low RCS ship, placed very close to shore (let say below 1nm), and high shore, like in fiords, would be at least a bit harder to spot?
At the moment I haven't noticed that effect. If it isn't there I would stop using "fancy" tactic and be surprised it doesn't work

Possibly the problem is when the detecting unit has both AS and SS sensors or have combined sensors (AEW).
Did a test with a P-3C (SS only) and the detection ranges indeed scale nicely with RCS:

P-3C Orion AN/APS-115]
Desgn Detection (NM) Description
SKUNK #16 20.4 Life raft (5m)
SKUNK #15 34.3 PB Toragh
SKUNK #14 49.5 LCS 1
SKUNK #13 52.0 PB Pegasus
SKUNK #12 51.8 LCS 2
SKUNK #11 53.9 DDG Zumwalt
SKUNK #10 60.7 FFG La Fayette
SKUNK # 9 67.5 PG OSA II
SKUNK # 8 87.3 PG Nanuchka IV
SKUNK # 7 91.7 PG Bora
SKUNK # 6 191.6 CGN 9 Long Beach
SKUNK # 5 199.5 CV Admiral Kuznetsov
SKUNK # 4 199.7 BCGN Kirov


But the same group is being detected by an E-2C grp0 within ~10 miles of each other, also detection order is half random. And even the life raft is detected at +200 nm.

E-2C [Sensors: AN/APS-138]
Desgn Detection (NM) Description
SKUNK #16 215.9 Life raft (5m)
SKUNK #15 219.4 PG OSA II
SKUNK #14 219.4 PB Toragh
SKUNK #13 219.3 PB Pegasus
SKUNK #12 220.6 PG Nanuchka IV
SKUNK #11 220.6 LCS 1
SKUNK #10 221.0 PG Bora
SKUNK # 9 223.2 DDG Zumwalt
SKUNK # 8 223.1 CGN 9 Long Beach
SKUNK # 7 223.1 LCS 2
SKUNK # 6 223.1 FFG La Fayette
SKUNK # 5 226.2 BCGN Kirov
SKUNK # 4 227.9 CV Admiral Kuznetsov


I'd guess the AS sensor is detecting these surface targets as air targets.

Attached the two test scenarios and two saves (just after skunk#16 is detected).

Have registered a ticket on this one, thanks guys [8D]

#Grumble - I guess it is bit more complex. Bear D Big Bulge A is detecting Nimitz at 248nm, Skjold at 212nm, and life raft at 165nm. It isn't AS radar, detection range is scaling in right direction, but effect of reduced RCS is quite different than for P-3C - but it also different from E-2. I am not aware of any technological advantage of Big Bulge A over AN/APS-115 to explain this, but possibly there is something I am missing.

Nice work guys. We think we know what the issue is and will work to resolve it. Not a trivial fix though so could be some time.

Thanks!

Mike

How does RCS factor in with AS radars at very high altitudes. I would think that any ship would have a very large RCS from a high altitude.

A ship has a large RCS compared to a plane, but the ship is sitting on water, so the SS radar must pick her reflection out of the clutter.

ORIGINAL: #Grumble
A ship has a large RCS compared to a plane, but the ship is sitting on water, so the SS radar must pick her reflection out of the clutter.

Thank you. We include clutter in our radar model. This is not HC.

As stated, we are looking into it.