Must be an FAA regulation.
Found this in CAP 778:
Omnidirectional departures shall be promulgated in the UK IAIP Part 3
AERODROMES (AD) AD 2.22 in accordance with the following example:
Climb straight ahead MAG track 051° to 1500ft then
turn on track climbing to enroute safety altitude/ MSA.
PDG 3.3%
For Isle of man no such info is published.
