Sanmar delivers first tug with CAT AVD hybrid solution

Written by Nick Blenkey
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Tug is the latest evolution of the highly successful RAmparts 2400-SX design

Turkey’s Sanmar Shipyards has delivered the Boğaçay XXXVIII, its 200th tug built to a design by Robert Allan Ltd. The delivery marks both a milestone in a working relationship of 25 years and a further advance in tug technology.

The Boğaçay XXXVIII is the latest evolution of the highly successful RAmparts 2400-SX design and incorporates the newly developed Caterpillar Advanced Variable Drive (AVD) hydro-mechanical hybrid propulsion system.


The tug is joining Sanmar’s own towage fleet in Izmit Bay, Turkey, where it will not go unnoticed. It has been painted with a bright green hull and colorful flowers on the deckhouse inspired by pop artist Andy Warhol’s “Flowers” print. Sanmar says the paint job is “reflective of the changing trend towards reduced environmental impact from tugs” and “is bound to attract much attention in the usually moribund world of tugboat aesthetics!”

Particulars of the new tug are as follows:

  • Length overall: 24.40 m
  • Beam, molded: 11.25 m
  • Depth, molded: 4.38 m
  • Maximum draft: 5.40 m

The vessel is classed by ABS with the notation:


Tank capacities are:

  • Fuel oil: 72.4 cu.m
  • Fresh water: 10.8 cu.m
  • Fi-Fi foam: 6.6 cu.m


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 at 1,765 kW at 1,800 rpm, and/or from two 435 kW hydraulic motors powered by a single CAT C32 auxiliary engine, rated at 1,081 kW at 2100 rpm. The power is delivered to two CAT MTA 627 FP Z-drive units with 2.7 meter diameter fixed pitch 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 fixed pitch propeller pitched for bollard condition at 0 knots, full power can be taken from the engine when free running, much like a controllable pitch or diesel electric system.

In the words of Nathan Kelly, Caterpillar Marine Product Definition Engineer: “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 Diesel Electric Propulsion (DEP) system at a fraction of the cost and size.”

Other advantages include improved response and acceleration as well as lower overall maintenance costs due to significantly reduced operating hours on the main engines.

Notably, with this system the engines are smaller than would normally be the case in a tug of this power (3512 vs. 3516 engines). The additional power to achieve maximum bollard pull comes from the C32 engine that also drives the Fi-Fi pump. The machinery configuration and power flow scenarios for the four operating modes are illustrated below:


Towing gear consists of ;

  • DMT Type TW-E 250KN electric double drum hawser winch with a pull of 250 kN at 0 – 9 meters/minute on low speed and 80 kN at 0 – 28 meters/minute on high speed
  • Data Hidrolik tow hook
  • Data Hidrolik 5 tonne aft capstan


The vessel has been outfitted to Sanmar’s usual very high standards for a crew of six people. The main deckhouse contains the galley, mess, two officer cabins, and a common WC. The lower deck contains two double berth cabins, a laundry, galley stores, and a common WC space. The wheelhouse provides all round maximum visibility and exceptional visibility to the bow and side fendering. The engine room features a small, sound resistant switchboard room.

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

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