Formally, course is not commanded using compass directions (north, south, east, west) in mil-speak, too long and too easy to mis-interpret. You rather give the course in degrees, 0° heading north, going clockwise 90° east, 180° south and so on. So in a proper military order, the terminology would be

Neuer Kurs: 0 Grad!

Or, even more snappy:

Kurs 000! (null-null-null)

See here: https://de.wikipedia.org/wiki/Kommandos_in_der_Schifffahrt

Kurs Nord and Richtung Norden would be fine, but don't really sound professional. The "German friend" who said "Segeln Norden" should undergo a thorough background check - He might be spying for some foreign power, because that is definitely not German.

Formally, course is not commanded using compass directions (north, south, east, west) in mil-speak, too long and too easy to mis-interpret. You rather give the course in degrees, 0° heading north, going clockwise 90° east, 180° south and so on. So in a proper military order, the terminology would be

Neuer Kurs: 0 Grad!

Or, even more snappy:

Kurs 000! (null-null-null)

See here: https://de.wikipedia.org/wiki/Kommandos_in_der_Schifffahrt

[Neuer] Kurs Nord! and Richtung Norden! would be fine, auf Nordkurs gehen as well, but don't really sound professional. The "German friend", however, who proposed "Segeln Norden" should undergo a thorough background check - He might be spying for some foreign power, because that is definitely not German.