Replacing a KTA38 850HP @1800 with a Mitsubishi S6R2-Y3 and S12A2-Y1

Replacing a Cummins KTA38 with a Mitsubishi S6R2-Y3 and S12A2-Y1

Replacing a Cummins KTA38 rated at 850 HP with a Mitsubishi S6R2 or S12A2 requires close attention to cooling capacity, hatch access, and engine-room width. Based on field experience, the S12A2 aligns well with the 850 HP rating in terms of BTUs, fuel burn, and general size, while the S6R2 offers a mechanically simple alternative for operators wanting a 6-cylinder platform. A key consideration is that Mitsubishi engines—particularly the S12A2—are wider than the KTA38, and past repowers have required removing secondary pumps or bracket assemblies to fit the engine through vessel hatches. Because the KTA38 often sees failures or major maintenance around 25,000–30,000 hours, many operators are turning to the longer lifecycle and higher reliability seen in Mitsubishi's S-series engines.

Power & Configuration Differences

Metric	KTA38 Tier 1	Mitsubishi S6R2-Y3	Mitsubishi S12A2-Y1
HP Rating	850HP @1800 RPM	803 HP @ 1400RPM	850HP @ 1940RPM
Configuration	V-12	Inline 6	V-12
Displacement	38L	29.96 L	33.93L
Weight	9300 lbs	6393 lbs	7452 lbs
Fuel System	N/A	Mechanical	Mechanical
Bell Housing	Typically 0	N/A	Double 00
Fuel Burn	42.8	N/A	N/A

Dimensional Delta: KTA38 vs Mitsubishi S6R2 and S12A2

Spec	KTA38	S6R2 (Delta)	S12A2 (Delta)
Length	84 in	–13.96 in	+6.2 in
Width	58 in	–14.97 in	–1.4 in
Height	82 in	–15.29 in	–18 in

Common Modifications to Plan For

Propeller Modifications Likely
Many KTA38 repowers require propeller changes to properly absorb the Mitsubishi engine’s power curve. Pitch adjustments or complete propeller replacements may be needed, depending on vessel loading and existing prop specs.
Possibility of Reusing the Existing Propeller
In some cases, operators have successfully run sea trials using their original KTA38 propellers, even when new props were ordered. The S12A2 has shown the ability to turn a larger prop than expected on paper, so final prop decisions should be based on sea trial performance rather than assumptions alone.
Accurate Propeller Data Is Critical
Many older vessels no longer have reliable prop specifications due to decades of undocumented swaps. Proper repower planning requires confirming real prop dimensions, pitch, cup, and blade area—not estimates.
New Engine Pedestals / Mounting Pads
Mounting footprints differ from Cummins, so new pedestals or structural adjustments will be required.
Piping Modifications
Expect rerouting of under-engine piping, front piping, or side piping, depending on the vessel layout.
Cooling System Additions or Changes
The S12A2 may require added cooling—such as an additional aftercooler circuit—as demonstrated in previous installations.
Air and Exhaust Adjustments
Some installs require new mufflers or added air intake capacity to meet airflow and backpressure requirements.

Target Markets

This is a viable repower option anywhere a KTA38 is currently working. These engines are widespread across multiple sectors, and ongoing issues with parts availability, long lead times, and declining reliability make Mitsubishi a strong alternative. If the vessel floats, it is essentially a target market.

Key segments include:

Inland river push boats operating high annual hours and needing dependable mechanical power.
Harbor and coastal tug boats looking for stronger durability and easier long-term maintenance.
Offshore tugs and supply vessels where uptime and service access are critical.
Ferries and workboats that benefit from consistent torque delivery and reduced electronic failure points.

IRR Companies with KTA 38 Boats (As of February 2022)

Company	Quantity
Kirby Inland Marine LP	248
Blessey Marine Services, Inc.	106
LeBeouf Bros. Towing LLC	52
Enterprise Marine Services LLC	35
Canal Barge Co., Inc.	28
Marquette Transportation Co. Gulf-Inland LLC	20
American River Transportation Co. LLC	20
Turn Services LLC	16
Buffalo Marine Service, Inc.	14
Ingram Barge Co.	14
D&S Marine Service LLC	12
American Commercial Barge Line LLC	12
Centerline Logistics Corp.	12
Zito Companies	11
Devall Towing & Boat Service	10
Carline Companies	8
Wepfer Marine, Inc.	8
Marquette Transportation Co. Gulf-Offshore LLC	8
Amherst Madison, Inc.	6
Superior Marine, Inc.	6

Third-Party Stories & Field Results

Brennan – S12A2 Success on the Elizabeth Ann

Brennan Marine has now completed two successful S12A2 repowers on KTA38-powered vessels, including the Elizabeth Ann.
In both cases, the operators reported:

Significant real-world fuel savings, enough that Brennan states every future repower will move to Mitsubishi.
Simplified maintenance, since their crews can work on the engines themselves rather than relying on OEM service delays.
Reliable performance, even in cases where the original propellers were used temporarily — the S12A2 still passed sea trial requirements.

Brennan emphasized that, for their dredge and towing operations where they purchase their own fuel, the long-term operating savings are substantial enough to standardize on Mitsubishi for the fleet.

Osage Marine – Fleetwide Adoption of Mitsubishi S6R2

Osage Marine in St. Louis operates a fleet of roughly 17–19 vessels. All but three are already Mitsubishi-powered, with the Wendy Ann being one of the most recent repowers using the S6R2.

Key takeaways from Osage:

Operators consistently report strong performance and lower fuel burn after switching to the S6R2.
Six-cylinder engines replacing older V-12s have delivered dramatic improvements in lifecycle cost and crew satisfaction.
Osage intends for their fleet to reach 100% Mitsubishi, including replacing older Cummins or Detroit units as they fail.
Even a vessel currently on charter (the Legacy) will be converted to Mitsubishi power if it becomes part of their fleet.

Their feedback is consistent: Mitsubishi gives them the reliability, maintainability, and operating cost stability they cannot get from modern Cummins or CAT offerings.

Why Operators Choose Mitsubishi Even With Upfront Work

Repowers from Cummins or CAT to Mitsubishi often require changes to piping, cooling, mounts, and sometimes gears. Even so, many operators are choosing Mitsubishi because the long-term savings are far greater than the installation effort.

A major driver is engine life. Many fleets are frustrated with engines that only last 30,000–40,000 hours before needing full replacement. After one or two engine swings, operators have already spent what a single Mitsubishi installation would have cost—without gaining the longevity Mitsubishi provides.

Operators are also reporting 30–35% better fuel economy in real-world use. Even when published fuel burn numbers appear higher on paper, performance at matched horsepower often shows Mitsubishi running more efficiently on-vessel. This becomes a major advantage for operators managing tight fuel budgets or negotiating fuel-sensitive contracts.

In short, despite the upfront repower work, Mitsubishi engines deliver longer life, lower operating cost, and better real-world efficiency, making the investment well worth it for many fleets.

Service Challenges with Cummins KTA Engines

Operators are increasingly frustrated with long service delays on Cummins equipment. What once took a day or two is now commonly 7–10 days before a technician can get to the vessel. With downtime costing $3,000–$5,000 per day, a simple issue like a failed sensor can quickly turn into $30,000–$50,000 in lost revenue.

These delays don’t even account for parts shortages, which can push downtime even further. After experiencing a few of these events, many operators realize they have spent enough in lost operation to justify a complete repower. This growing pain point is a major reason fleets are moving away from the KTA platform and toward more service-friendly mechanical alternatives.

Repower Planning Summary

Primary Required Changes

New engine mounting pedestals
Propeller modifications may be required to capture full available power
Possible gear ratio changes depending on existing RPM setup (1940 → 1600 / 1800 differences)
Rerouting of piping under, around, or forward of the engine
Cooling system adjustments, including potential addition of an aftercooler circuit
Removal of auxiliary components (secondary water pump, bracketry) if needed for hatch clearance

General Observations

Both Mitsubishi options fit the 850 HP KTA38 market well, with the S12A2 matching load and cooling needs closely and the S6R2 offering a strong inline alternative depending on vessel layout.
Propeller performance is highly vessel-specific—while modifications are often expected, several real-world installs passed sea trial without new props, showing surprising flexibility in the S12A2’s torque curve.
Installation complexity varies by vessel type, especially older boats where hatch clearance, secondary pumps, and unknown prop history require more careful measurement and planning.