Just for others here, this is very misleading:

1) Sailboats (even moderately sized ones) often do not show on radar at all.

2) 30nm is probably way too optimistic, at a height of 50ft your line of sight is only about 8-9nm. Radar is LOS.

3) 11m is a terrifyingly short time, even if this was all correct

4) you can't identify things based on radar alone, and there's no way you can make out what something is even at 5nm.

5) there's no way you can see a boat at 10nm lol