Here are the speeds and distances your sonar man is telling you in the language your mother taught you in.
CONTACT RANGE IN METRES
Short range: 0-1,000
Medium range: 1,001-3,000
Long range: 3001-20,000
CONTACT SPEEDS IN KTS
Slow: 1-7
Medium: 8-18
Fast: 19-34
Very Fast: 35-
This holds true for everything except Merchants and Convoys medium and fast speeds which are:
Medium: 8-11
Fast: 12-