Page 44: of Marine News Magazine (September 2015)

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BOAT OF THE MONTH

Figure 1: Thrust Vector Diagram for Carrousel-RAVE vs. Figure 4: CRT can be used in any Attitude

Conventional VSP Water Tractor with Equal Effectiveness or side tug and how in the ? rst two scenarios line ten- sion remains essentially constant regardless of tug po- sition or attitude. As a bow tug, the CRT is uniquely capable of safely braking the tow in the manner illus- trated. Critically, the heeling forces are mitigated by the action of the Carrousel system. The hydrodynamic forces created during such maneuvers are very high, with the result that thrust delivered by the engines and drives can be signi? cantly reduced at towing speeds, thus reducing fuel consumption and emissions. Model

Figure 2: tests demonstrated that a compact 32 meter CRT with

CRT as a Bow Tug.

Gross Tonnage below 500 can generate a line force in excess of 160 tonnes at 10 knots with a maximum heel angle of approximately 15°, in which case only 2,800 kW (3,753 bhp) is applied.

Figures 5 and 6 illustrate how the line forces devel- oped by the CRT compare to a conventional VSP trac- tor as a function of propeller pitch setting. Another very unique feature of this design is the fact that in en- closed or con? ned waterways such as locks and canals, the VSP drives adapt almost instantaneously to turbu- lent ? ow conditions, such as those induced by combina- tions of ship and tug wash, as well as the wash re? ected off the con? ning walls. The longitudinally symmetrical propulsion con? guration can also be used to control a tow in the con? ned environment of a lock, by placing the tug perpendicular to the tow and then precisely di- recting the propeller wash as required to keep the tow

Figure 3:

CRT as a Stern Tug.

off the lock walls. Combining all these features with the very fast (approx. 4 seconds) thrust response time of the

VSP drives compared to a typical 12–14 second time for thrust reversal of a Z-drive makes the CRT concept extremely reliable and ensures the highest possible stan- dard of ship control in such con? ned conditions.

As a consequence of this detailed research and study, a complete new design has evolved, which was intro- duced to the tug industry in London in May 2015.

Announcement of a construction contract for the ? rst of class CRT 3200 is, according to Robert Allan Ltd.,

September 2015

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