Your radar will have "Weather" and "Search" mode. Weather mode is optimised to pick up returns from precipitation and the gain is fixed to ensure a red target on the screen equates to the density of precipitation typical of a thunderstorm. It's not perfect and very heavy precipitation from non thunderstorm cells will also show red.
Weather mode will also show large ships and rigs up to a range of up to circa 60nm depending on altitude and preciptitation. As one gets closer to the target, one has to tilt the scan down which can cause the target to merge into the sea returns if it is rough.
"Search" mode is for ground mapping and detection of small objects. In this mode the gain can be adjusted which will allow sea returns to be reduced and better definition of the target(s). Usually when you select shorter ranges (<20nm) the pulse length will reduce and the repetition rate will increase. This will help create a better defined target. Some units also have different Search modes to cater for different ranges and may have a sea clutter filter. Small fishing boats will show as a very small return but supply boats and larger vessels/installations will show as quite a large target depending on the amount of gain you have selected.
In practice, one has to balance tilt and gain to give the best return. Typically (depending on the type of radar) one should be able to track a target down to approx 1/4nm before it becomes unusable but North Sea rules requires us to be visual with the target by 3/4nm otherwise we must abort the approach and climb back to MSA while at the same time turning away from the target.