Radar detection is the same whether the target is a ship or an aircraft, or whether the seeking radar is on a ship or an aircraft. So if you want to make the ship 'stealthy' you just have to apply the same shaping tactics as you would for the aircraft.
On the one hand...The major difference here is that the ship is not as maneuverable as the aircraft and that the ship is limited to 2D space while the aircraft have 3D scope. That mean any for any radar contact with a ship, there will be more time to data process and detect the ship.
On the other hand...Precisely because the ship is limited to 2D maneuvers, any seeking radars on the ship will be limited by the horizon if it is a ship-to-ship engagement, or a shore-to-ship engagement.
Try this...
Horizon calculator - radar and visual
You can vary the altitude (H) as much as you like. But say we have two ships each with the same radar antenna elevation, say 10 meters for example, then each ship would have the maximum radar horizon of about 26 km distance out. So if you have one ship that is shaped for 'stealth', that ship would appear to be a very small target and perhaps small enough to be discarded as a non-threat.
That is why the Zumwalt is alleged to appear as small as a fishing boat -- black squares -- in a ship-to-ship or shore-to-ship engagement.