i understand ...it's OK and thanks for the criticism!!!
I think M/S ( Motor Ship) it's used general for all motor propelled ships!!! ...there are also some specific prefixes such as :
B/C = Bulk Carrier
F/B = Ferry Boat
C/S = Cruise ship
C/V = Container Vessel
M/T = Motor Tanker
and more...
But i thing u have right ...they are more specific prefixes which the most people do not know...so it's better to use the M/S for the next drawings general!