Tug design adapted for oceangoing and offshore towage

OSD-IMT’s anchor-handling towage vessel design includes an S-bow and additions to the hull for improved stability

Naval architects at OSD-IMT have developed a design for a compact anchor-handling towage vessel with considerable bollard pull. OSD-IMT utilised designs for oceangoing towage vessels from Wijsmuller Engineering and enhanced them for the latest towage requirements.

This created the OSD-IMT7501 design as a modern interpretation of the legacy Tempest design. OSD-IMT managing director Lodewijk van Os believes this design fills a void at the lower end of the offshore and deepsea towage market. It combines the power and performance of larger towage anchor handlers, but is more compact, which lowers construction costs. It has an overall length of 51 m and a maximum bollard pull of 120 tonnes.

“Our Wijsmuller design legacy has been an inspiration for developing this new generation of compact oceangoing tug,” Mr van Os told Tug Technology & Business.

OSD-IMT7501 is suited for project towage and supporting installation and decommissioning activities for the oil, gas and renewables markets.

“Our Wijsmuller design legacy has been an inspiration for developing this new generation of compact oceangoing tug” 

In developing the design, architects at OSD-IMT incorporated an S-bow concept with flexibility that enables engineers to amend the bow’s transverse profile to suit specific performance requirements.

Using an S-bow means OSD-IMT7501 has improved waterline entry angles and smoother vessel motions, which result in higher crew comfort. The S-bow flares out towards the top, giving reserve buoyancy forward in rougher seas and providing a practical forecastle deck.

Another addition to the design is a knuckle at the waterline of the aft- and midship sections of the vessel. This delivers a narrower waterline beam that reduces sailing resistance and provides reserve buoyancy adding to the stability of this tug during anchor-handling operations, or in case of heeling.

The freeboard of the working deck was heightened compare with similar sized vessels to reduces the influx of seawater on the aft deck and add to the stability.

Designers reviewed the layout of working spaces on board to create safe working environments and provide better access to equipment. They also expanded the accommodation to provide space for the 14-20 crew to spend their off-watch time.

OSD-IMT7501 can be tailored to suit different owner requirements and anticipated operational conditions. Working space layouts can be changed and different engineroom and power generation systems added. A hybrid propulsion and power system can be incorporated to reduce emissions and improve operational efficiency.

The knuckle on the OSD-IMT7501 hull features on many of OSD-IMT’s Azistern tug designs and is the result of extensive tank testing. The latest Azistern designs are for tugs with hybrid propulsion. Azistern-e series ranges 20-26 m in overall length and have bollard pull capabilities between 35-75 tonnes.

Azistern 2035e is the smallest of three hybrid propulsion tug designs at 20 m long with a design draught of 3.75 m. It has a bollard pull of around 35 tonnes and is suitable for smaller harbours and inland waterways.

OSD-IMT’s Azistern 2250e has a length of 21.45 m, draught of 4.6 m and bollard pull of 50 tonnes for operations in terminals and harbours. If an operator needs a terminal tug with more power then it could use an Azistern 2575e design with a design capability of 75 tonnes of bollard pull from a 25-m tug.

These designs feature batteries and diesel-electric arrangements for lower fuel consumption and emissions and fewer running hours when compared with diesel-only driven tugs.

* Wijsmuller Engineering became WorldWise Marine and is now part of OSD-IMT. Wijsmuller Engineering designed Tempest in 1976