Replacing a QSK38 1000HP and 1300HP @1800RPM with a Mitsubishi S12R-Y3 1100HP and 1260HP @1600RPM

Replacing a QSK 38 with a Mitsubishi S12R

This comparison evaluates the Cummins QSK38 Tier 3 and Mitsubishi S12R-Y3 platforms using continuous-duty ratings intended for unlimited-hour operation. The 1000 HP QSK38 aligns most directly with the S12R-Y3 at 1100 HP @ 1600 RPM as a practical repower option for common inland applications, while the 1300 HP QSK38 can be addressed with the S12R-Y3 at 1260 HP @ 1600 RPM with similar modification requirements. Differences in operating speed, bell housing configuration, and cooling demand drive the primary conversion considerations, but overall repower scope remains consistent across both ratings.

Comparison to the S12R-Y3

Attribute	QSK 38	Mitsubishi S12R-Y3
Tier	3	3
Power	1000HP @ 1800RPM 1300HP @ 1800RPM	1100HP @ 1600RPM 1260HP @1600RPM
Configuration	V-12	V-12
Displacement	38 L	49 L
JW (BTU/min)	17181 (for 1000HP)	N/A
AC (BTU/min)	8812 (for 1000HP)	N/A
Fuel Burn (GPH)	50.6 (for 1000HP)	N/A

Dimension Delta Comparisons:

Dimension	QSK 38	S12R-Y3	Delta
Length	90.0 in	94.13 in	+4.13 in
Width	62.0 in	59.54 in	-2.46 in
Height	88.0 in	68.78 in	-19.22 in

Brief Background: Cummins QSK Series

Cummins KTA 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.

Common Modifications to Plan For

Engine Room Fit & Piping
The Mitsubishi S12R is approximately 4 inches longer than the QSK38. A repower survey is required to identify potential obstructions and confirm clearance. Rerouting of existing piping is common due to the added length and different engine layout.

Cooling System
The S12R has higher overall heat rejection compared to the QSK38. Additional cooling capacity is typically required.

Aftercooler and grid cooler replacements are commonly needed
Existing jacket water cooler may be reusable, but must be verified on a case-by-case basis.
All cooling components must be evaluated during the repower survey.

Gear Ratio & Drivetrain
The S12R operates at 1600 RPM versus 1800 RPM on the QSK38.

Gear ratio change is required when replacing the QSK38 with the S12R.
Gear ratio changes may not be required for the higher horsepower replacement, but must still be evaluated.
Drivetrain changes are a standard part of this repower class.

Bell Housing Adapter
The QSK38 uses a single 0 bell housing, while the S12R uses a double 00 configuration.

An adapter plate is required to mate the existing gear to the S12R
Adapter plates are mandatory and cannot be omitted
In some cases, adapter costs are included as part of the gear ratio change.

Propeller Modifications
Propeller changes may be required to absorb the additional horsepower when replacing the 1000 HP QSK38 with the 1100 HP S12R.
Minor prop adjustments may also be necessary for the 1300 HP to 1260 HP comparison.

Exhaust System
The S12R requires a larger muffler than the QSK38. Exhaust piping modifications are commonly required to support increased flow.

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 38 Operators IRR as of March 2022

Operator	Qty
Maritime Partners LLC	34
Kirby Inland Marine LP	29
American River Transportation Co., LLC	28
Genesis Marine LLC	24
Enterprise Marine Services LLC	16
D&S Marine Service LLC	10
Dupre Marine Transportation, Inc.	8
Blessy Marine Services, Inc.	6
Turn Services LLC	6
Marine Chartering	4
E-Squared Marine Service LLC	4
NGL Marine LLC	4
Central Boat Rentals, Inc.	4
American Commercial Barge Line LLC	4
General Marine Services LLC	4
Buffalo Marine Service, Inc.	4

Sales Strategy

Core Pain Point: Engine Life

The primary pain point with Cummins QSK engines is engine life, especially on the QSK19 and QSK38.
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 QSK and 50 platforms.
Customers consistently express dissatisfaction with this lifecycle for continuous-duty operations.

Failure Type Observed

Failures are often major bottom-end failures, not just top-end wear.
Reported failure areas include:
- Crankshafts
- Main bearings
- Connecting rod and rod bearings
These failures tend to occur earlier than expected and often require full engine replacement.

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 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:

Minor increase in overall engine length
Cooling system evaluation and potential upgrades
Drivetrain adjustments due to lower operating RPM
Bell housing interface changes
Propeller adjustments
Exhaust system modifications

General Observations

The S12R is a larger displacement engine operating at lower RPM, which drives most of the repower considerations.
Physical differences are concentrated in length and cooling demand rather than width or height.
Both QSK38 ratings follow the same repower path, with only minor differences in drivetrain and prop setup.
The 1000 HP QSK38 is the more common inland rating and aligns cleanly with the 1100 HP S12R.