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200th RAL-DESIGN SANMAR TUG FEATURES NOVEL CAT PROPULSION

Saturday, January 25, 2020 

Turkish shipyard Sanmar and Canadian designer Robert Allan Ltd (RAL) recently celebrated the commissioning of the 200th tug built by Sanmar to a RAL design.

RAL says that achieving this milestone in just over 25 years is remarkable, and a testament to the close working relationship developed by these two businesses in the international tug market. The success of Sanmar reflects commitment to the highest standards, building well-researched designs of high quality from RAL.

The new 2.4m x 11.25m tug will initially join Sanmar’s towage fleet in Izmit Bay, Turkey. It has been built to ABS class, with notation ✠ A1, TOWING VESSEL, ✠ AMS, ✠ ABCU, UWILD, QR, UNRESTRICTED SERVICE, BP (70 tonnes)

The 200th tug, Boğaçay XXXVIII, is the latest evolution of the successful RAmparts 2400-SX design, and this latest vessel bucks the current trend for electric hybrid propulsion by incorporating the newly developed CAT Advanced Variable Drive (AVD) hydro-mechanical hybrid system.

The CAT AVD system consists of a pair of dual input, continuously variable transmissions, located in the shaftlines between the main engines and the Z-drives. The AVDs can accept power from the CAT 3512 main engines, rated 1765kW at 1800 rpm and/or from two 435kW hydraulic motors powered by a single CAT C32 auxiliary engine rated 1081kW at 2100 rpm. The power is delivered to two CAT MTA 627 FP Z-drive units with 2.7m diameter FP propellers.

A primary advantage of the CAT AVD system is the continuously variable transmission which can modulate propeller speed down to 0 rpm like a slipping clutch. It can also spin the propeller up faster than would be possible if the engine was directly coupled to the drive, allowing the engines to operate in their peak efficiency zone instead of operating along the propeller demand curve at higher specific fuel oil consumption, thus resulting in significant fuel savings. With a FP propeller pitched for bollard condition at 0 knots, this feature enables full power to be taken from the engine when free running, much like a CP or Diesel Electric Propulsion (DEP) system. Other advantages include improved response and acceleration as well as lower overall maintenance costs due to significantly reduced operating hours on the main engines.

Nathan Kelly, Caterpillar Marine Product Definition Engineer, said: “This (AVD system) allows propeller speed independent of engine speed so optimal engine efficiency can be achieved leading to fuel savings of fifteen to twenty percent. Basically, all the benefits of a variable speed DEP system at a fraction of the cost and size.”

It is noteworthy that with this system the engines are smaller than would normally be the case in a tug of this power, the additional power to achieve maximum bollard pull coming from the C32 engine, that also drives the firefighting system pump.

On trials, Boğaçay XXXVIII achieved 70.35t bollard pull and a free running speed of 13.3 knots.

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