Rotortug Magazine

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If you think good design is expensive, you should look at the cost of bad design



Rotortug magazine, published by Rotortug. June 2018 Editorship Rotortug B.V.

Production, Text & Design FreeLans B.V.

Photography Rick Groen, Jacco van Nieuwenhuyzen, Marijn van Hoorn, Rob Hinton, Damen Shipyards and FreeLans B.V.

Illustrations Sjors van Roosmalen


Segers, Schiedam - The Netherlands

Rotortug B.V. is the company specializing in the design and marketing of the world wide patented Rotortug design. The Rotortug distinguishes itself from the conventional ASD, Tractor or Voith Schneider designs by using a triangular propulsion configuration. The excellent maneuverability of this type of tug is superior to all other conventional designs. The Rotortug has been recognized as the preferred tugboat design in many ports across the world.


ROTORTUG MAKES THE DIFFERENCE Towage is a developed marine service providing control ability to marine pilots. Many misconceptions on our industry prevail. Tug design is often focused on maximizing power in favour of maximizing the effective application of that power. The working principle of the Rotortug relates to the triple Z-drive configuration: two azimuthing thrusters located in the front and one in the back. Since her introduction the highly maneuverable Rotortug has been selected for the most challenging jobs around the world. The choice of the optimized tugboat configuration cannot only make the difference in safety and maximizing operational efficiency. It also makes sense in operational and capital expenses; it could be the difference in winning or losing a contract. We believe in tug designs that overcome deployment hurdles, with high leverage and effective pull, connecting day-to-day experience from the tug crews with our engineering knowledge base and continuously improving on that. By anticipating future client wishes, the flexibility to change when needed and the emphasis on long term relationships with our clients, we are able to continue to grow and prosper in the very competitive tugboat market. In this magazine we start to tell how Rotortug B.V. started in 1996 and developed into an independent company with strong partners to best serve our clients. You can read about tug deployment, the operational gains, our nautical consultancy and about saving costs. And of course you’re welcome on our training tug RT Borkum to experience the working principles of the Rotortug in full operation and discover how unique the Rotortug is! Managing Director of Rotortug B.V.


Evan Willems


How it all started 4 | Tug deployment 9 | How does the Rotortug work? 16 | Saving money 24 | Operational gains 25 | Nautical consultancy 28 | Our business 30



HOW IT ALL STARTED Rotortug was established in 1996 as the shipbuilding and trading arm of KOTUG International, a renowned tugboat company with its head office in Rotterdam, the Netherlands. KOTUG realized how innovative design could impact its towage service on an operational level and how an optimized tugboat configuration enabled KOTUG to provide the same service level with fewer tugs. On these basic premises, KOTUG developed the Rotortug with a triple Z-drive propulsion arrangement, mounted in a triangular configuration. This highly maneuverable tug was designed to escort ships at all speeds ranging from 0 to 10 knots and to assist ships in very confined spaces, without being affected by current or propeller wash. u 5

Since her introduction, the Rotortug has been selected for the most challenging of jobs around the world. After a 10-year period of design and construction of over 20 Rotortugs to strengthen KOTUG’s market position, the Rotortug triple Z-drive configuration was acknowledged by other tugboat companies. To make the Rotortug available for other companies and to secure a ‘Chinese Wall’ between our KOTUG affiliation and prospective clients, Rotortug decided to work together with the best design house and shipyards.

Robert Allan Ltd. Naval Architects To create a more independent position, Rotortug teamed up with the internationally respected Naval Architect Robert Allan in 2012. With the input of 75 years of towage experience, over 100 years of design experience combined with latest techniques available in various fields of expertise, Robert Allan and his team designed the Advanced Rotortug (ART) series with distinguished looks, superior operational performance and maximum safety in mind. u

Simplicity is the ultimate sophistication. 6

Rotortug values long term relations and will always advise with this vision in mind. 8

Long term relations Now clients can obtain a custom Rotortug design with a license fee directly from Robert Allan Ltd. With this custom design, the client can build at their preferred shipyard and with their preferred equipment, serviceable in their respective areas of operation. Before making a final investment decision, Rotortug can be consulted to assist in establishing, or reviewing the preferred tugboat configuration.

TUG DEPLOYMENT Optimizing operational efficiency of a tug system requires an in-depth understanding of the assisted vessel’s working principles and capability. This means defining real clearly what is intended by a service and how it relates to the used tool, or deployed tug, especially when it involves multiple tugs working together in a team effort. Tug deployment in this scope relates primarily to ship handling and escort towage to assisted vessels.

Within this scope ‘assisted vessels’ are not dead ships, but have a limited maneuvering capability or

Control ability of sea going vessels at decreasing speed

control ability. This control ability is supplemented by the tug’s propulsive power and/or vector forces (towing on a line, or pushing) projected to the assisted vessel. As such it is imperative to understand how assisted vessels move and pivot at different speeds. The tug system is an integral part of a marine pilot’s toolbox. Individual tugs provide the marine pilot with external vector forces. u 9

Full control with two tugs.


DEFINITIONS Ship handling: Providing direct mode steering- and braking forces and propulsive power at speeds below 6 knots for limited periods of time. l Escort towage: Providing (tethered) steering- and/or braking forces at speeds between 10 to 6 knots. This definition specifically excludes untethered tugs maintaining an exclusion zone. l Bollard pull: Maximum towline force at zero knots speed provided by a tug’s propulsion power. l Steering force: Effective transverse force provided to an assisted vessel by a tug. l Braking force: Effective longitudinal braking force provided to an assisted vessel by a tug. l Tug: A tug providing a ship-handling service. l Escort tug: A tug providing escort towage and ship-handling services. l Tug system: One or multiple tugs providing control ability to an assisted vessel. l Assisted vessel: Vessel with limited maneuvering capability and/or propulsion and assisted by one or multiple tugs. l Direct mode: Using a tug’s propulsion power to provide a towline force. l Indirect mode: Using the leverage between a tug’s skeg, hull form and propulsion power to provide a towline force. l







forward as reasonably possible is using tug designs not suited for

A marine pilot aims to maximize advantageous 2 . Both in relation this position, in adverse (wave) tug leverage and the net effective to leverage and because the tug conditions and not applying a safe vector force. With the assisted vessel propeller wash will avoid the assisted approach to the assisted vessel when under speed this means predomi- vessel mostly. This phenomena is also establishing the towline connection. nantly using an escort tug to provide known as ‘jet-impinged thrust’ from Therefor many tug masters prefer steering- and/or braking forces at propeller wash pushing against the to deploy to the ‘shoulder’ 3 speed. Steering forces are generated assisted vessel’s hull 3 .

position. Very safe for the tug, but

by deploying the indirect mode

not very effective within the scope

relying on hydrodynamic (lift) forces Deploying to the most forward, of providing a control ability to the to generate the vector force 1 . or centre-lead forward position, assisted vessel with jet-impinged Given the nature of hydrodynamic at speed can be precarious when thrust losses and poor leverage. u lift forces the net effective steering force drops rapidly when the assisted vessel slows down during its approach. The marine pilot cares about the provided vector forces only, regardless of speed, and tugs should preferably be designed to provide steering and braking

To benefit from the centre-lead fore position, tug designs should be able to safely

force capability across all speeds.

establish a towline connection

At slow speed the forward tug gains

and work in close proximity to

importance. Maximizing leverage connecting the forward tug as far

the assisted vessel. 13

Full control with two tugs.

We value our tug crews. Tug designs within the bow pressure wave field primary performance capability is should be suited to operate safely of a laden tanker or bulk carrier.

addressed in bollard pull. Bollard

in close proximity to the assisted

pull is the straight pull at zero knots

vessel, to establish a towline The marine pilot demands a vector, speed that a tug can achieve with its connection at high speeds and a force, impacting the assisted towline connected to a fixed point adverse conditions. This means good vessels movement. To this end tugs (representing the assisted vessel). course controllability in the sailing were rated by their installed power At speed, assessing performance direction and the capability to in days past. A feasible solution with characteristics of a tug is generally always move to a safer position. all tugs fitted with similar propulsion associated to the steering and/or From steering clear from an under- technology, but with development braking forces applied as a stern water bulb at 10 knots, to operating of different propulsion concepts the tug. 14

Tugs should be designed to provide steering- and braking force capability across all speeds.

To the marine pilot, vector force is key. Not how the vector force is

Performance in dierent modes

generated. The Rotortug provides a marine pilot and tug master with two different operating modes to create steering and/or braking forces at all speeds and work within his safety zone.



TUG DEVELOPMENT SINCE 1996 We believe in tug designs that overcome deployment hurdles, with high leverage and effective pull. We connect day-to-day crew experience with our engineering knowledge base and continuously improve on that.

A balancing act

the propeller-wake interaction, or

Advances in computational fluid thrust deduction to predict expected dynamics enable us to assess a bollard pull. It also relates to course tug’s characteristics during the controllability sailing ahead and design phase of a hull form. astern. Evaluating tug-handling Comparing hull forms is not just characteristics over a wide range about evaluating hull resistance, of variables provides increasingly or providing an indication on balanced tug designs. u


Conventional Unstable

ASD (Ahead) Unstable

Z-drive tractor Stable

Tug handling is in many ways a balancing act, characterized by the location of a tug’s propulsion point, the underwater application point of its installed power and towing point, the last towline contact point. With this mechanic in mind, two types of arrangement can be identified:

The stable equilibrium provides the best tug-handling characteristics and safety envelope during a straight pull. 18

Unstable, high concentration Types: Conventional tug and ASD (Ahead) l High concentration and effort l Limited safe working zone l Not suitable for ship-handling

ASD (Astern) Stable

Rotortug Ahead Stable

Rotortug Astern Stable

The stable equilibrium provides the best tug-handling characteristic and safety envelope during a straight pull, also referred to as 'direct mode' and is therefore predominant in modern day ship-handling tugs. Tug designs with their propulsion point on one side amidships (ASD and tractor tugs), therefor have a single feasible ship-handling working end only. The impact of this balancing act is that a tug will be sailing astern depending on whether being deployed as a front – (ASD), or stern tug (Tractor).

Stable, simple tasking Types: Voith tractor tug, Z-drive tractor tug, ASD (Astern) and Rotortug l Always capable of moving to a safer position l Suitable for ship-handling

The Rotortug features a close to midship propulsion point, pulling ahead or astern in a ship-handling capacity, sailing ahead, operating bow first, irrespective of its deployment. u 19

Indirect escorting with Rotortug.

About leverage: Escort towage

For maximum leverage, the towing point is shifted backwards as far as

Marine pilots require a vector force possible, skeg area is increased at to oppose rudder failures for vessels the expense of maneuverability and at speed. Direct mode application of the skeg is moved as far forward as that vector by a tug is not effective possible. Also the generated towline at speeds >4 knots for ASD and force creates a high heeling moment tractor tugs. To create a sufficiently and the tug’s capability to deal big vector force, naval architects with this heeling moment, limits the use leverage and the tug’s hull generated vector force. In other form hydrodynamics and skeg words, size matters, or more arrangement to generate a vector specifically tug displacement and force. This is also commonly tug stability are key to provide referred to as ‘indirect mode’. 20

effective indirect mode vector

forces to the assisted vessel. Tug

Steering and braking force at 10 knots

design follows developments in engine- and propulsion technology. In 1996, when the first Rotortug was developed, the Rotortug provided a cost-effective way to increase the tug’s bollard pull by adding a third Z-drive given the available engine technology at the time. In 2000 the first Rotortug escort trials were conducted with the first generation Rotortug, RT Magic. effectively in direct mode up to such, the direct mode (sometimes A key observation during these trials 8 knots. A key benefit of the direct referred to as combi-arrest at 6-10 was that the RT Magic had the mode is that the towline force does knots) provides tug users with a capability to continue operating not create a heeling moment and as less stressful operating mode. u


Design is not just what it looks like and feels like. Design is how it works.

Direct escorting with Rotortug.

Improving on this concept, the fifth pleasing tugs provide pride and generation Rotortug, RT Evolution, joy to tug crews, creating an an ART 80-32 design, conducted full engagement between the tug scale escort trials in 2015, pushing fleet and service they provide. direct mode operating speed up Combining our ‘soft’ design touch to 10 knots. The ART 80-32 was with high power leverage and our designed for both direct- and partner's engineering base, we indirect mode (escort) operations, create great tugs. with indirect mode providing maximum steering forces to the assisted There is a fundamental disconnect vessel. The Advanced Rotortug (ART) between what is an effective tug as series distinguish themselves by perceived by the marine pilot (being providing the tug master and one of many tug-users) and what is marine pilot with multiple operating perceived to be a pleasant tug to solutions to suit their preference.

work with by tug crew. Our focus on user-centric design is rooted in

A soft touch, hard power

our operator family background.

Creating user-friendly designs Our commitment is to create tugs improves safety on board, reduces that are: (1) highly effective (2) a crew fatigue and improves opera- pleasure to work with and (3) provide tional


Aesthetically good stakeholder value. 23


Rotortug is designed with a holistic approach to the towage service. The Rotortug excels in all towage services, ranging from escorting, ship handling and confined space jobs. With performance, safety, reliability and happy fit people as part of our holistic approach to towing, considerable cost savings are made by deploying Rotortugs. The investment in and deployment of new tugs should be considered

Three 80t BP tug total life-cycle costs

within this system-based frame. In the end the overall efficiency, reliability and profit resulting in a successful project outcome. This success starts with getting the right tools for the job and the capital expenses (CAPEX) that come with it. CAPEX is important and in that respect a Rotortug over 65 tons should not cost more than any other system with the same bollard pull. The initial costs are divided over smaller engines and smaller thrusters, which saves on CAPEX. Four 65t BP tug total life cycle costs The shipyard however has to install three instead of two thrusters and engines, so the larger part of the savings are consumed in that process. What you buy for CAPEX is more important; a very versatile, reliable and performing tug under all circumstances. CAPEX is a small but important part of the overall costs structure under consideration during the tender phase of a project. The larger part of the calculations of the project price is related to operational expenses (OPEX). OPEX can be considered in two ways; per tug or for the operation in total. More often than not the OPEX is considered per tug, we look at the OPEX


for the whole multi-tug operation. In this way you can achieve considerable costs savings. Three Rotortugs are able to provide the same service level


as four ASD or tractor tugs in most circumstances. High speed escort jobs, low speed escort jobs, ship handling, firefighting, pilot transfer, buoy or


hose handling, can all be done with Rotortugs so no additional or specialized equipment is needed for that. Overall efficiency is accomplished by creating

Fewer, more powerful tugs reduce OPEX

an open mind.

and total life cycle costing.


Tug selection is impacted by all the previously listed considerations, combining nautical, operational and economic impact factors, with (nautical) risk management remaining the principal purpose. The optimized tug fleet provides stakeholders with a lot of added value, which at first may not seem apparent.

OPERATIONAL GAINS The optimized tug configuration times are guaranteed. The marine mode to be effective, to the range provides added value to any pilot’s principal interest is with where they can only perform in nautical operation. Deployment of vector forces supplementing his direct mode, requires repositioning. the suitable tug for the operation vessel’s control ability. Quick vector With the right choice of equipment provide pilots with more leverage force response is key in limiting lost from the toolbox such unwanted and maneuvering possibilities, time when a tug is repositioning, events can be avoided and overall subject to the general conditions improving safety boundaries or nautical safety is increased. u such as geographical or environ- limiting additional precautions. mental constraints. Typically a push pull job, requires

Ship handling: Vector response

constant repositioning of the tugs. Also a job with decreasing speed

The marine pilot doesn’t have to from the range that ASD or Tractor compromise and quick turnaround tugs have to perform in indirect 25

Picture above: ASD/Tractor operation. Picture below: Rotortug operation.

Great design is not just a solution, it’s the elimination of the problem. 26

Confined spaces: Vector force

or indirect mode at all speeds. Providing sustained- and higher

The marine pilot operates a vessel vector forces compared to ASD

Bollard pull (-%) at zero speed under different towline angles Bow

anywhere between 0 and 10 knots. or tractor tugs in all working To create a balanced tug design, conditions, while enabling crews tugs provide the assisted vessel to work within their comfort zone. with control ability anywhere in this range. Sometimes the marine The ability to always move to a safer pilot is happy that tugs are capable position and consequently deploy of providing a control ability at all. to the most effective centre lead Confined spaces restrict ASD and fore and aft configuration, creates


tractor tug’s capability to provide a a systematic advantage using fewer vector force. Rotortugs can provide tugs to provide the same service a vector force independent of tug level. A focus on overall operational heading and sailing direction.

efficiency on both the system and individual tug level, creates

This signature Rotortug feature increasingly effective tug systems. enables the Rotortug to provide a vector force within the beam of the assisted vessel. Providing the marine

Bollard pull (-%) pushing at zero speed in different directions

pilot with sustained vector control during lock or bridge transits and full control of the assisted vessel.

Control ability The Rotortug offers marine pilots a tool that can be used in either direct 27

Terminals or ports are multimillion investment decisions. Most of these decisions relate to (wet) infrastructure and land based equipment, to accommodate the vessels who visit to load or discharge valuable cargoes. Mitigating navigational risk in relation to these investments is thus the principal purpose of a towage service. The selection of the optimized tugboat configuration contributes to this principal purpose.

NAUTICAL CONSULTANCY Risk assessment and navigational expensive or not effective to different solutions and barriers to simulations are often only included complete the job at hand, would mitigate the associated hazards in a back-end phase of a project you ever find out? Risk assessment and top events involved. development. Sometimes even only does not provide a true or false after tug procurement! Now if some statement in relation to an opera- Substantial value can be added consultant would recommend you tions safety (or risk aversion). Instead by integrating our maritime toolover-powered tugs, too big, too it should identify and quantify box during early infrastructure 28

development with high impact on maneuverability, various towing nautical consultancy can benefit infrastructure optimization and techniques, to optimize the total your project. In cooperation with decision-making. A structured and terminal package.

the various partners Rotortug can

transparent approach exploring

advise and assist in the marine

your options beyond international These are but a few of examples of side providing as a total marine guidelines. Smaller turning basins how a structured and transparent package. save your dredging expense. Short breakwaters by making fast at higher speeds impact capital expenses. Smaller channels, or bigger vessels calling your port because of better steering force capability, due to the best tugboat configuration, exactly determined with the relevant parameters such as bollard pull,

Assisted vessel, Basic MET conditions, Basic Bathymetry, Serviceability level Advanced bathymetry and Advanced MET conditions

TIer 1 Desktop calculation Tier 2 - Fast-time simulations

Scenario-driven Non-normal operations

Tier 3 - Real-time simulations, human factors

Towage solution


Rotortug is a networked partner. In this business for the long term we favour long lasting client relations over short term third-party gains. We also believe in the strong relationship with our partners. Transparency is another important issue; no third-party cash-flows! Any stakeholder or direct client can commission a Rotortug design with our naval architect partner Robert Allan Ltd. To benefit from our knowledge and experience and use the collective intellectual property of the Rotortug system they will also have to purchase a one off per Rotortug License fee.

We secure an extensive knowledgebase about towage, the towing industry, her operations, stakeholder interests and the operational restrictions of existing tug types. By connecting our operator history and experience-base feedback with research data gathered from full scale, and model tests and CFD studies, we create the best possible fit for purpose tug designs. We provide our clients with a substantial level of operational assistance and guidance during the design and construct phase of a project and can connect you with any company in our industry, from Z-drive and main engines manufacturers, to certified tug master training. Simulator and/ or on the job training can be provided through our partner TTC BV (Tug Training and Consultancy BV), an iso certified tug training company specialized in Rotortug training.



If you think good design is expensive, you should look at the cost of bad design and engineering. 31

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