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Caterpillar Marine has announced a collaboration with Sanmar Shipyards in Istanbul, Turkey, to build a tugboat with a hydraulic hybrid propulsion system - the patented Cat Marine Advanced Variable Drive (AVD).

The AVD system is designed to provide improvements in both fuel efficiency and vessel performance through a fully integrated hydro-mechanical propulsion system.

"Different from a typical Power Take In (PTI) solution, the AVD incorporates a planetary gear set allowing seamless clutch engagement of main engines, auxiliary engines, or both to provide a scalable power installation to meet any customer need in terms of maximum vessel speed, power, or bollard pull," explained Nathan Kelly, product definition engineer for Caterpillar Marine. "This also allows propeller speed independent of engine speed so optimal engine efficiency can be achieved leading to fuel savings of fifteen-to-twenty-percent. Essentially, all the benefits of a variable speed Diesel Electric Propulsion (DEP) system at a fraction of the cost and size."

The AVD system is built to be flexible and to accommodate multiple configurations. According to Caterpillar, Auxiliary engines can be utilized to accommodate low load or transit operations greatly extending time to overhaul and reducing service costs on main engines. Electric motors can be used instead of hydraulics if required. Diesel engines can be substituted by natural gas engines as the AVD system provides superior vessel performance regardless of engine load acceptance. Main engines can also be downsized with supplemental power provided via auxiliary engines or generators if electric motors are used.

The Sanmar hydraulic hybrid tug will be a Robert Allan-designed RAmparts 2400SX harbour tug incorporating an integrated Caterpillar AVD system of 3512 main engines, a C32 auxiliary engine, Cat MTA 627 fixed pitch tug thrusters, and bridge controls. The vessel will carry Fifi 1 designation with 70T metric bollard pull.

The AVD system will also include a fully integrated controls system with customizable operating modes and display panels at the bridge.

Compared to a conventional tug with equivalent bollard pull, the return on investment (ROI) is estimated at three years or less based on projected fuel and operating cost savings.