Why can a twin-screw vessel often berth and unberth with less tug assistance than an equivalent single-screw vessel in similar conditions?

A. The independent control of differential thrust between the two shafts gives the Master direct control over turning moments and limited lateral movement without relying on rudder effectiveness (which requires forward/aft speed) — capabilities a single-screw vessel typically cannot replicate without bow/stern thrusters or tug assistance

B. Tug assistance is never required for any twin-screw vessel under any conditions

C. Twin-screw vessels are inherently lighter and therefore easier to manoeuvre regardless of propulsion configuration

D. The reduced tug reliance has nothing to do with propulsion and is purely a function of vessel size

A. Twin-screw vessels are always faster than single-screw vessels of the same size, which is their only real advantage

B. Twin-screw vessels are unaffected by wind or current, unlike single-screw vessels

C. Differential thrust — running the two propellers at different speeds, or in opposite directions, generates a turning moment independent of rudder angle or forward speed, giving far greater control in close quarters, including the ability to turn the vessel almost in place

D. There is no meaningful manoeuvring difference between twin-screw and single-screw vessels

A. By running one propeller ahead and the other astern with both rudders turned toward the same side (often "outward" relative to the direction of intended lateral movement), the resulting forces can largely cancel fore-and-aft motion while combining to push the vessel sideways — the exact technique and rudder angles vary by vessel, but the principle is using opposed thrust plus rudder deflection to convert rotational/thrust forces into a net sideways force

B. It requires both propellers to run at identical speed and direction with rudders centred

C. Twin-screw vessels cannot move sideways under their own power under any circumstances and always require tug assistance

D. Walking sideways is achieved purely by wind effect and has nothing to do with engine or rudder configuration