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TUGTECHNOLOGY25-26 October 2021London

Day 2 | Paper 8

IntroductionSeaways 24 (IMO: 9768576) is an anchor handling tug delivered for multipurpose offshore duties to Seaways International in August 2016 by Keppel Singmarine, a wholly-owned subsidiary of Keppel Offshore & Marine.

Designed as part of the RAmpage 5500-ZH class of Infield Support Vessel by Robert Allan Ltd, the 55 m loa vessel is equipped for a variety of offshore duties, including tanker handling and berthing, SBM holdback and floating hose handling. It features Class 1 and 2 fire-fighting capabilities, as well as Class 1 oil recovery capabilities.

Delivered as the fifth in a series of tugs by the builder, the capabilities of Seaways 24 were upgraded at the request of charterer BP, during the build phase, significantly increasing bollard pull from 100 tonnes to 120 tonnes-plus to fulfil service requirements in deep water operation in Block 31 west of Angola.

In order to meet these raised performance needs with minimal disruption, Berg Propulsion undertook a review of propulsion options in combination with its design, build and end-customer partners before recommending the integration of a novel hybrid diesel-electric solution.

In the resulting set-up, propulsion is provided by the original two 3,000 kW MAK 9M25 (750 rpm) main engines and Caterpillar gensets coupled to two Berg Propulsion MTA8 Z-drives. The drive trains turn two CPP propellers of 3.4-m diameter in nozzles.

However, power is boosted by additional electric motors positioned in the drive train to achieve 120-tonne bollard pull in ahead and 15 knots in free running, hybrid mode. The vessel is capable of 7 knots under electric propulsion alone.

After five years of almost continuous service in deep water, the 9,548 bhp vessel has accumulated approximately 30,000 running hours per main engine and 40,000 running hours per azimuth thruster – working for more hours than most harbour tug thrusters put in over the course of a vessel lifetime.

This paper outlines the considerations driving the original decision-making process, but also the experience gathered over a five-year period in consequence of decisions made. It focuses on a distinctive solution which achieves the integration of diesel electric propulsion fuel efficiencies with minimal disruption.

SYNOPSISOn an early Saturday morning in August 2016, the multi-purpose hybrid tug, Seaways 24, set out to break a bollard pull record in Singapore. As the tug featuring the largest hybrid propulsion solution azimuth capability installation in the world at that time, the newbuild delivered a remarkable 124 tonnes of bollard pull during trials, before being deployed straight into 24/7 operations supporting a FPSO operation for a five-year period off the coast of Angola.

This paper provides a review of the circumstances which required Berg Propulsion to undertake a significant upgrade in tug power after the start of the construction phase. It covers analysis of build options, challenges and benefits, and results gathered from five years of operating experience which offer key insights into the future optimization in tug performance.

What were the lessons learned from building a first of its kind vessel and, based on five years of working experience, how have the operational benefits come to life?

Emil Cerdier (speaker/author), Jonas Nyberg (co-author), Berg Propulsion

A practical review: five years of 24/7 hybrid tug operations

Figure 1: Seaways 24, delivered in 2016

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1. Upgrade optionsInitially envisaged to fulfil a bollard pull requirement of 100 tonnes, expectations for the performance of Seaways 24 were upgraded in response to charter requirements part-way through the construction project, to 120 tonnes-plus. The requirement came after the engines and azimuth thrusters had already been sourced by the yard (Keppel Singmarine), creating a specific challenge for the owner and the installation, of fulfilling a higher specification with minimum changes to the vessel configuration.

As the relevant provider of control, automation and propulsion technology, Berg Propulsion deployed its VesselCalc analytics software (Figure 2) in support of a rigorous evaluation of alternative concepts to weigh up the pros and cons of different options.

VesselCalc takes inputs from contractual requirements, the vessel’s operational profile (hours of operation per year, percentage of time anticipated operating in standby, dynamic positioning, transit modes). These inputs are refined with reference to details such as the resistance data for the hull, propulsion system performance (power, number and size of propellers, rpm), plus the power generation and conversion system including the main engines, gensets, shaft alternators and any batteries or booster motors.

VesselCalc produces a report on which to base a comprehensive comparison between optional configurations.

Three options were considered as viable alternatives to meet the needs of the charterer and owner.

Option 1: Larger main engines with higher power to raise the bollard pull. This alternative would entail new thrusters and would also require an altered shaft line solution and a complete revamp of the machinery space.

Option 2: Much larger thrusters to deliver higher bollard pull at the existing power. This solution would require an increase in propeller diameter and thruster size that would have been impractical in relation to the existing hull.

Option 3: Keep the engine and drive line intact and add electrical boosters aft of the azimuth thrusters. In this case, the original main engine and drive line remain but the

azimuth thruster would need to be replaced with a higher rating to allow for the inclusion of additional power, to be supplied via an electric motor.

Given the progressed nature of the project, Option 3 offered itself as the simplest and most straightforward solution, despite its highly unconventional basis. VesselCalc’s evaluation resulted in a solution featuring the specifications shown in Figure 3.

2. Operating requirementsDespite its appeal, Option 3 created its own challenges. While the new thruster solution would now be able to absorb 3,560 kW (3,000 kW main engines plus 560 kW electric motors) into the Berg MTA 834 CP azimuth thrusters, for example, the existing vessel configuration would have insufficient electrical capacity to power the 2 x 560 kW electric motors.

Solving this challenge involved beefing up the existing 3 x C18 gensets to a set up comprising 1 x C18 and 2 x C32, in order to deliver in excess of what the two motors could absorb. The main switchgear also needed an upgrade, in order to make room for the bigger generators and the feeders for the large PTI motors.

As noted, the upgrade was initiated to fulfil requirements from the charterer for increased bollard pull but, beyond simply delivering more power, the concept selected is distinguished by its ability to offer far more much more functionality than the original configuration. In

Figure 2: VesselCalc comparison methodology for alternative concepts

Figure 3: Changing requirements

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fact, the vessel’s setup now offers three main propulsion modes:

Diesel modeDiesel mechanical mode, where the main engine drives the propeller directly. This mode is most often coupled with the shaft alternator so that all other gensets on the vessel can be shut off. In this mode, the setup achieves its original 100 tonnes of bollard pull.

Electric modeTwo propellers run electrically with the main engines clutched out. The propellers can be run at a much-reduced rpms (even below main engine idling speeds), greatly boosting the efficiency of the system at low loads. The power comes either from the gensets or one of the main engines running decoupled and powering the main switchboard via the shaft alternator.

Hybrid modeIn this mode the propulsion system runs at variable speed, with additional power drawn from the gensets via the electric motors. This ‘boost’ means 120 tonnes-plus of bollard pull is available, with the propulsion control system determining the power balance between diesel and

electrical contributions, for best possible fuel consumption/acceleration or other needs.

In addition, it is fair to note here that the solution can provide electrical propulsion in case of main engine downtime, where systems redundancy equates to enhanced safety for those on board.

3. Construction considerationsWhere hybrid solutions are concerned, a common approach taken by some builders is to buy elements of the system from separate vendors and then ask the vendors to work on systems integration. This often works well at the detailed level in terms of creating step-by-step solutions for signal interfaces and mechanical connections.

However, this practical approach can result in shortcomings where overall vessel performance is concerned. For example, it is not necessarily based on the capabilities originally agreed between the owner and the ship’s designers. Pragmatic solutions – taken individually but often experienced collectively – are unsystematic and do not consider whether the vessel will behave as intended, or whether levels of automation are in line with crew expectations.

Figure 4: Three modes of operation: Diesel mode (top), electric mode (middle), hybrid (bottom)

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Projects of the type under discussion include high expectations for automation and control, but also involve multiple stakeholders. It is therefore essential to create a common understanding on systems functionality and operations which is robust enough to bear scrutiny at both the conceptual and detailed levels from different standpoints, from specification to sea trials.

The value of the holistic, or integrated approach can be seen by considering different transitions from electrical to mechanical modes which on the surface could be perceived as largely equivalent. Let’s take a moment to review the following scenarios:

Scenario A: Mode transition is possible from any lever position and irrespective of the engines running while the vessel maintains its speed.

Scenario B: Mode transition is only possible if the correct engine has been started in advance and while the vessel is stationary.

Both of these scenarios will yield a system that ‘works’ and delivers on the vessel’s specification in terms of speed and bollard pull. However, Scenario A is much more likely to enable the crew to use the system to achieve the savings and vessel performance projected in a real operational situation.

In the case of Seaways 24, the lead time between deciding what equipment to install and delivering the vessel was approximately seven months. This put considerable pressure on the delivery of the Berg MTA 834 CP thrusters and demanded decisiveness in aligning

expectations on how the vessel would function.

A distinctive aspect of the Seaways 24 project is worthy of separate note: the collaborative approach taken by Seaways through the build process proved key to meeting revised project objectives. The owner involved seagoing personnel at every step to promote understanding of the vessel’s specifics, also taking a proactive approach to training – even during the construction phase. This approach would pay dividends in terms of vessel utilisation and efficiency.

4. Engineering analysisTo meet the construction goals outlined, the development process adopted aligned requirements before the engineering phase. This meant developing a structured approach for the operator, the yard and other equipment makers to agree on a range of factors in advance - including the level of automation and functionality - to ensure that all stakeholders shared the same vision, goals and roadmap (Figure 5).

This process also defines the level of automation for the vessel using a language and level of detail that any operator of the vessel can understand and focuses on how the interface on the bridge works rather than what the signal interfaces are. This document and process is also used for the actual FAT, HAT (Harbour acceptance trial) and SAT (Sea acceptance trial).

In a simplified example, the vessel’s operation description dictates that mode transition from electric to mechanic mode can be done from any lever position, at any vessel speed and regardless of whether the main engines are running or shut down.

Figure 5: Systems-based development process for stakeholders

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In the HAT subtest, this could be experienced as running the vessel in electric mode at 7 knots while initiating the mode transfer and validating that vessel continues uninterrupted. Expressed in this way, the process seems obvious and straightforward, but practical experience from multiple projects indicates that focus is put on signal interfacing between sub systems rather than the functional aspects affecting the crew. This often results in systems that are either difficult to use or will not enable the operation as intended at the vessel concept stage .

5. Operational experience 2016-2021After delivery to Seaways International, Seaways 24 was deployed into service in deep water at Block 31 off the coast of Angola, operating with a crew of 14 and including an additional electrical officer. The vessel has subsequently accumulated approximately 30,000 running hours per main engine and 40,000 running hours per azimuth thruster. As well as having the ability to reach a speed of approximately 7 knots in electric-only mode, the configuration delivered achieves increased redundancy over conventional vessels working in the field.

In general, feedback from Seaways covers the smooth integration of Seaways 24 into operations off Angola, based on the collaborative approach taken by the owner and awareness of relevant seagoing personnel through the build stage. Seaways has also expressed itself as highly satisfied with the additional systems redundancy available to the hybrid solution, where electrical drives can be used as backup in case of main engine downtime.

However, information covering running conditions also demonstrate consequences for operating costs: the owner reports that operations are sustained for the majority of the time using a single engine, resulting in significant gains in terms of fuel efficiency over comparable vessels.

Specifically, data analytics provided to Berg Propulsion

for Seaways 24 as of April and May 2021 prompt the following observations:• Seaways 24 total hours April-May 2021: 1,464. Total

operating hours 1,436 (98.1%)• Seaways 24 total accumulated main engine running hours

1,958h (1,012h + 946h). • Conventional 2ME operation would demand running hours

of 2,872h.• Conventional vessel would consume between 9%

(operating with one engine + one azimuth in standby mode) and 40% (operating with two engines + two azimuths in standby mode) more fuel.

• Seaways 24 runs 59% in DE mode on one main engine with shaft alternator, 41% in DM.

• Seaways 24 255h accumulated running hours on gensets (2xC32 and 1xC18). In standby they normally have no genset online.

• Alternative of running 2 ME with low pitch (poor efficiency) or one engine/one propeller (relatively poor efficiency and parasitic drag from one propeller).

The very high utilization rate of 98.1% covers the period when at least one engine is running and, as the numbers also show, the vessel ran for 59% of the time on a single main engine with shaft alternator.

In standby operation, the hybrid setup can draw on the frequency drive rather than the main engine, allowing the propeller to run much more slowly and improving the propeller’s hydrodynamic efficiency against a conventional solution, reducing power and saving fuel.

Combined, these factors yield estimated fuel savings ranging between 9% (single engine/single thruster) and 40% (twin engines, twin thrusters). Considering standby mode alone, dual engine operational savings may be closer to 50-60%, given the inefficiencies associated with the conventional setup when two propellers are operating at extremely low pitch.

In addition to fuel savings, the greater proportion of time spent running on a single engine represents a maintenance gain due to the total number of accumulated running hours on the main engines.

Figure 6: Seaways 24 has been operating off Angola on charter since 2016 at Block 31

Figure 7: Final configuration, propulsion setup for Seaways 24

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ConclusionThe expectation is that there will be an accelerated shift to electric powered propulsion units. Adapting battery power solutions and fuel alternatives to marine diesel will open up to deliver greater flexibility in performance and optimized energy efficiency, as well as achieving compliance with new rules and regulations. In addition, technologies developed in other industries are quickly being adapted to the marine market.

Remote monitoring and access to vessels and equipment will also be key factors in maintaining uptime and efficiency. Being able to monitor, evaluate, trouble shoot and even control equipment from remote location opens up a range of new services and solutions.

These developments will also change the way businesses operate and we will see new class requirements, new suppliers and new crew competencies, as new solutions challenge old standards.

If shipping’s transition to make greater use of electrification is well underway, opportunities for deployment will require

ingenuity from suppliers to nurture available opportunities.

As the Seaways 24 project demonstrates, one key to meeting this challenge is to maintain focus on the separate but linked themes of product, system and operational efficiency, as well as the overall benefits accruing through integration. In the case at hand, we can consider these drivers in relation to different stakeholders as:• Product efficiency to meet charter’s requirement for

significantly increased installed power• System efficiency with regard to being able to operate in

high and low power modes with maintained or elevated performance and switch between modes as required as efficiently as possible

• Operational efficiency by crew education and helping the crew to understand and get insight into how the vessel works with being involved in the design process via the initial work with the vessel operation description

The case under discussion also crystallises the critical contribution personnel and training can make to the build process, especially where operating choices have consequences for best performance.

Figure 8: Strategies for optimised efficiency