Rendezvous Calculations on ship

Cruise vessel – GMT 21 30
Cruise vessel speed – 23 knots
Find out next day sunrise at GMT, so Difference between GMT is the time (hour)
Total distance = time * speed

True course = 260 degree. So, course is SW 80 Degree

Find out dlat in degree. How? 0° 275.022° * cos 80° = 0° 47.76′ S
Find out dep in nm. How? 275.022 * sin 80° = 270.86′
Find out dlong in degree.

Dep = dlong * cos m’lat
M’lat = Initial lat – (d’lat/2)

Initial lat and Final lat same name = dlat (-)
Initial lat and Final lat difference name = dlat (+)
(Opposite formula with dev and variation)

Initial lat and Final lat same name, mlat = (1st + 2nd)/ 2
Initial lat and Final lat difference name, mlat = (1st – 2nd)/ 2

Sinco = (Dep / Dist)
Cosco = (dlat / Dist)
Tanco = (Dep / dlat)
Dep = dlong * Cos m’lat