Wartsila’s Innovative WSD 4628 Anchor Handling Tug Supply (AHTS) Design

Another Stunner from Wartsila

Wartsila launched a fresh, innovative Anchor Handling Tug Supply (AHTS) vessel design at the Sea Asia Exhibition held at Singapore from April 21 to 23, 2015. The company predicts the design to slash fuel use by up to 20-25% vis-à-vis traditional diesel mechanical four engine systems with a proportional trim down in emission levels.

Sea Asia is the premier maritime event in Asia that witnesses the convergence of a cross section of the global shipping community. Sea Asia 2015 was hugely successful with 16,185 participants from 85 countries. Once again, this importance of Singapore as a leading global maritime center stood emphasized.

Efficient and simple, the vessel uses less fuel and leaves behind lower environmental footprint. It is particularly compatible with large and medium AHTS equipped with a 2-speed gearbox. Such a gearbox is a crucial part of large-medium AHTS for it slashes the cost and complications without cutting back on operational safety.

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WSD 4628 AHTS Vessel Design (Source: http://www.wartsila.com/media/news/21-04-2015-wartsila-launches-new-innovative-ahts-vessel-design-at-sea-asia-exhibition)

AHTS vessels tow an oil rig to and from its destination and transport supplies to and from rigs. Sometimes, they serve as Emergency Rescue and Recovery Vessel (ERRV). The winches of AHTS vessels tow oil rigs. Once the rig is in position, the AHTS’ anchor handling equipment drops the rig’s anchor and keeps the rig steady.

Technical & Other Details

Designed for a bollard pull of 180tons, the WSD 4628 AHTS vessel comes with options for 150tons or 220tons of bollard pull. The design boasts of a hybrid propulsion system and a 2-speed gear box built in accordance with American Bureau of Shipping (ABS) and Safety of Life at Seas (SOLAS) norms.

Hybrid diesel-mechanical and diesel-electric propulsion system with 2-speed gear boosts efficiency when operating at fluctuating loads. Directly driven mechanical parts lose less power during transmission at higher loads. Generating power from both main engines and gen-sets with load-optimized engines is advantageous at low loads.

On account of optimization of engines for various loads, this design consumes 17% less fuel as compared to

Data Sheet of the WSD 4628 AHTS

Data Sheet of the WSD 4628 AHTS

twin-engine, diesel-mechanical propulsion system. Special hull contours hike fuel savings to 25%. Engine-Load optimization results from:

  • electric boost during high bollard pull mode
  • smooth load sharing with 4 medium-speed engines and mode selection in Power Management System (PMS)
  • electric propulsion during low power mode
  • steaming on both main propellers from one main engine or gen-set

Design Features:

  • Based on Proven Technology
  • Lower Fuel Consumption and Emissions with optimization of engine with loads
  • Economical
  • Safe and Easy Operations via seamless load sharing through four medium-speed engines and mode selection in PMS
    WSD 4628 design does not require the crew to possess special electrical skills
    The hybrid, 2-speed gearbox PTI (Power Take In) feature enables smooth changeover between different operational modes with equal efficiency in all modes
    The design also ensures zero loss in PTO (Power Take Off) power during change in propeller speeds
  • Higher Redundancy and Reliability without addition of extra parts
  • Minimum Risk through integration of products with design
  • Flexible Selection of AHTS suppliers and equipment

The 2-speed gearbox:

  • Wartsila 6L32 Technical Data

    Wartsila 6L32 Technical Data

    saves fuel via low rpm operation of the CPP

  • diminishes propeller speed without affecting PTO speed and/or nominal engine speed
  • possesses twin screw AHTS with bollard pull up to 220tons
  • has a power range of 2-13MW

Wartsila 6L32 Engines

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Wartsila 6L32 Engine (Source: http://www.kitmondo.com/wartsila-6l32/ref482291)

Compliant with IMO Tier II exhaust regulations, Wartsila 32 engines were developed because the market required 320mm cylinder bore engines. The engines incorporate latest combustion technology for simple, efficient, and infrequent maintenance.

These engines offer great fuel flexibility, fast starting, high power-to-weight and power-to-space ratios, and high reliability.


Greener and cost-effective shipping is the order of the day and Wartsila has once again delivered the goods. You can hardly expect otherwise from an operator with over half a century of experience.