Between tugs, which position provides more leverage at slow headway?

Master the Navigation, Seamanship, and Shiphandling (NSS) – Officer of the Deck (OOD) Phase 2 Exam with engaging flashcards and multiple choice questions, complete with hints and explanations. Prepare comprehensively for your test!

Multiple Choice

Between tugs, which position provides more leverage at slow headway?

The main idea is turning moment: the yawing effort a tug can produce is the thrust times how far that thrust is from the vessel’s center of gravity (CG). The farther behind the CG the force acts, the larger the turning moment for a given thrust, which is especially valuable when headway is slow and the rudder is less effective. Placing the tug at the stern gives the thrust a long lever arm behind the CG, creating the greatest yawing moment to rotate the ship. A forward-positioned tug acts ahead of the CG and provides a smaller turning moment, tending to influence the bow more than the hull’s heading. A midship tug is closest to the CG, giving the smallest lever arm and therefore the least effect on heading. With no tug, there’s no additional moment to change direction.

The main idea is turning moment: the yawing effort a tug can produce is the thrust times how far that thrust is from the vessel’s center of gravity (CG). The farther behind the CG the force acts, the larger the turning moment for a given thrust, which is especially valuable when headway is slow and the rudder is less effective.

Placing the tug at the stern gives the thrust a long lever arm behind the CG, creating the greatest yawing moment to rotate the ship. A forward-positioned tug acts ahead of the CG and provides a smaller turning moment, tending to influence the bow more than the hull’s heading. A midship tug is closest to the CG, giving the smallest lever arm and therefore the least effect on heading. With no tug, there’s no additional moment to change direction.

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