Ch. 8 Flashcards
What hydrodynamic pressure zones are caused by the ships passage through the water?
High pressure at the bow, lower pressure alongside the ship and suction at the stern.
What are the hydraulic effects on the tug as it makes an approach close to a ship underway?
It draws the tug toward the ship by the suction aft and it pushes the tug away from the ship forward.
How should the tug handler compensate for these effects?
By pacing the ship long enough to see how the tug is affected and then gently easing the tug alongside. An experienced operator lets the tug be drawn in slowly by the suction aft with the helm turned slightly away from the ship, working the tug in from the hydraulic forces forward.
What is stemming?
Stemming can occur when a tug takes a towline from the bow of a moving ship. If the tug comes in contact with the ships sides it may loose steerage, in which case the tug may be caught by the ships bow and rolled over.
What are two common cases of stemming?
Misjudgment of the tugs set in towards the ships bow or oversteering as the tug transits through the ships pressure zones at its bow.
Should a tug ever back its engine when coming alongside a ship?
The tug operator should avoid backing when a tug is overtaking the ship to get into position to push or pull. When the tug backs its engine, the tug may not respond and can cause damage to itself and to the ship.
What three factors must a tug operator balance when maneuvering around ships?
Tug hull resistance, opposing forces, application of force to ship.
Hydrodynamic interaction between ship and tug are a function of which three factors?
Ship speed, displacement, and hull shape
