Melhor utilização dos rebocadores

Leia abaixo texto original citado na publicação Rebocadores Portuários (pg.42):

In this test, a 57,720 dwt vessel loaded to 33 ft. and a very powerful conventional twin screw tug (7,200 Hp / 220,000 pounds bollard pull) were utilized to illustrate the relative effectiveness of a tug working at the bow, quarter, and transom of a ship making headway. With the vessel at a speed of 5 knots, on a steady heading, and the rudder amidships, the vessel’s engine was stopped and the tug ordered to push at full power at each of the three positions. During each of the three runs the wind was on the port bow at approximately twenty-five knots. Measurements of the rate of turn in degrees per minute were noted. As shown on the illustration below, the rate of turn was 3 degrees/minute with the tug on the bow, 12 degrees/minute with the tug on the quarter, and 24 degrees/minute with the tug on the transom. This clearly demonstrates the superiority of utilizing a tug on the transom during an escort. It also shows that a single conventional tug is of limited use as an escort vessel at higher speeds if it cannot make up on the transom.

During this test, we noted that when the tug was working at the port bow, it could not get out to more than a 30º angle to the ship. This meant much of its force vector was an accelerative force versus a steering force. Very quickly, the vessel’s speed increased to 5.6 knots. After initially establishing a rate of swing of 3 degrees per minute, at 5.6 knots the swing of the vessel to starboard stopped, and the vessel started to swing back to port! The tug was still working at full power, but the vessel was responding in a fashion that was completely opposite to what was expected. While the forces involved in creating this action are not totally understood, the reaction of the vessel was clearly documented. This is an extremely important finding, as placement of an escort or assist tug at the bow is considered by many as the most prudent action.