Replacing a QSK50 with a Mitsubishi S16R

Replacing a QSK50 with a Mitsubishi S16R

This comparison evaluates the Cummins QSK50 and Mitsubishi S16R using continuous-duty ratings at 1,600 RPM. With both engines operating at the same RPM, the S16R presents a strong replacement option for the QSK50, offering higher displacement with minimal impact to physical size. While additional cooling capacity and system modifications are expected, the matched RPM eliminates the need for a gear ratio change, making this a practical high-horsepower repower path.

Jump to: 

• Comparison to the S16R
• Brief Background: Cummins QSK Series
• Common Modifications to Plan For
• Target Markets
• QSK50 Operators IRR as of March 2022
• Sales Strategy
• Repower Planning Summary

Comparison to the S16R

Attribute	QSK 50	Mitsubishi S16R
Tier	3	3
Power	1700 HP @ 1600 RPM	1675 HP @ 1600RPM
Displacement	50 L	65.37 L

Dimension Delta Comparisons:

Dimension	QSK 50	S16R	Delta
Length	109.0 in	115.4 in	+6.4 in
Width	62.0 in	60.0 in	-2 in
Height	88.0 in	77.2 in	–10.8 in

Brief Background: Cummins QSK Series

• Cummins KTA series engines were fully mechanical and long used in workboat and inland markets.

• The QSK series replaced the KTA line, introducing electronically controlled engines beginning in 2005.

• This transition marked Cummins’ shift from mechanical systems to electronic engine management.

• Some operators prefer mechanical engines for their simplicity, which has influenced repower decisions over time. 

• The QSK50 is positioned as a high-horsepower QSK platform, commonly rated at 1,700 HP @ 1,600 RPM in continuous-duty applications.

• With approximately 50 liters of displacement, it occupies a higher-power segment than the QSK19 and QSK38.

• While less common in inland service, the QSK50 remains relevant for vessels requiring high continuous horsepower.

Common Modifications to Plan For

Cooling System

• The S16R has higher displacement than the QSK50, which is expected to result in higher heat rejection.

• Additional cooling capacity is likely required to support the S16R.

• Cooling system changes may include:

  • Larger or additional grid coolers

  • Verification of existing cooler capacity during a repower survey

Exhaust System

• The S16R requires a larger muffler compared to typical QSK50 installations.

• Exhaust system modifications may include:

  • Upsizing the muffler

  • Verifying available space in the exhaust stack

Piping & Systems

• Rerouting of piping is expected due to differences in engine layout and cooling system configuration.

• General system reconfiguration should be anticipated when transitioning to the S16R platform.

Drivetrain & Gearing

• Both the QSK50 and S16R operate at 1,600 RPM.

• No gear ratio change is expected, making this a more straightforward repower compared to RPM-mismatched applications.

Physical Fit

• Although the S16R has greater displacement, the physical size difference is minimal, with the S16R being approximately 6 inches longer than the QSK50.

• Significant space-related modifications are not expected, but standard fit verification should be completed during survey.

Displacement & Engine Architecture Note

Across comparable horsepower classes, Mitsubishi R-Series engines carry significantly greater displacement than their Cummins QSK counterparts. On average, the R-Series platforms are approximately 24% larger in displacement at similar horsepower ratings. For example, the QSK19 (19 liters) aligns with the Mitsubishi S6R at 25 liters, the QSK38 (38 liters) aligns with the S12R at 49 liters, and the QSK50 aligns with the S16R at 65 liters. This increase in displacement reflects larger internal components and heavier rotating assemblies, which is a key factor when evaluating physical size, structural loading, and long-term durability at continuous duty ratings.

Target Markets

• Push Boats
• Tug Boats
• Crew Boats

QSK 50 Operators IRR as of March 2022

Operator	Qty
Southern Towing Co.	8
Kirby Inland Marine LP	6
Maritime Partners LLC	4
Jantran, Inc.	2
LeeBourgeois Towing LLC	2
Genesis Marine LLC	2
Enterprise Marine Services LLC	2
H & K Marine Service LLC	2
American Commercial Barge Line LLC	2
Illinois Marine Towing, Inc.	2
Ingram Barge Co.	2
Garber Bros., Inc.	4
McGinnis, Inc.	4
Superior Marine, Inc.	4
Carline Companies	4
Buffalo Marine Service, Inc.	4

Sales Strategy

Core Pain Point: Engine Life

• The primary pain point with Cummins QSK engines is engine life.

• Operators commonly report 25,000–30,000 hours before replacement. 

• In some cases, Cummins has stated directly that engines should be expected to be replaced around 25,000 hours, including references to QSK50 platforms.

  • During recent new-build discussions, Cummins communicated that QSK50 engines should be expected to be replaced around 25,000 hours.

  • This guidance was given in the context of three newly built triple-screw vessels, with Cummins indicating the engines were not expected to exceed 25,000–30,000 hours of service life.

  • The engines were described as replacement-cycle engines, rather than long-life assets.

• Customers consistently express dissatisfaction with this lifecycle for continuous-duty operations. 

Parts Availability & Support

• Parts availability is a frequent and ongoing complaint with Cummins.

• Customers report vessels being tied up waiting on parts, sometimes for months.

• Many operators feel Cummins customer service has declined significantly compared to past experience.

• Customers are often told supply chain issues may take 12–18 months to resolve.

Sales Approach: Let the Customer Talk

• Most customers are already experiencing pain and do not need to be convinced.

• Simply asking about:

  • Engine life

  • Parts availability

  • Downtime experience
    often leads customers to openly share frustration.

• Allowing customers to talk through their own experience naturally surfaces the issues.

Mitsubishi Positioning 

• Mitsubishi engines are positioned as:

  • Longer-life assets

  • Lower lifecycle cost based on observed service history

• Typical Mitsubishi experience discussed includes:

  • Top-end work at 20,000–25,000 hours

  • Engines operating 60,000–100,000 hours without bottom-end work

• Support is framed around:

  • Strong parts availability

  • Faster engine delivery timelines

  • Ongoing customer support

Objections: Modifications & Cost

• Required repower modifications can appear costly and become an objection.

• Examples discussed include:

  • Gear ratio changes

  • Grid cooler additions or upsizing

• The strategy is to compare one-time modification cost against:

  • Ongoing downtime

  • Repeated failures

  • Lost revenue from vessels being down

• Modifications are a one-time event, while engine-related pain is recurring.

Electronics & Control Dependency

• QSK engines are fully electronic, placing operators at the mercy of Cummins for:

  • Diagnostics

  • Service access

  • Resolution timelines

• Mitsubishi is positioned around:

  • Empowering customers and local service

  • Reducing dependency on factory service response by allowing work on your own vessel.

Repower Planning Summary

Primary Changes:

• Additional cooling capacity required due to higher displacement of the S16R

• Cooling system modifications, including larger or additional grid coolers

• Piping rerouted to accommodate engine and cooling layout differences

• Larger muffler required

• No gear ratio change expected (1600 RPM to 1600 RPM match)

• Minimal physical size impact, with the S16R approximately 6 inches longer

General Observations

• The S16R is a strong physical and RPM match for the QSK50, operating at the same 1600 RPM.

• Higher displacement of the S16R suggests improved durability potential compared to the QSK50.

• Repower scope is driven primarily by cooling and exhaust changes, not drivetrain modifications.

• While market opportunity is more limited, the QSK50 represents a viable repower candidate when encountered.