NEW Cummins Onan Marine QD 27MDKDU-8257A 27kW Diesel Generator for Sale

The Cummins Onan Marine QD 27MDKDU-8257A is a professional 27kW marine diesel generator engineered to provide dependable onboard electrical power for yachts, commercial vessels, passenger craft, workboats, sportfishing boats, and other demanding marine applications. Part of the established Cummins Onan Quiet Diesel range, this generator combines a durable four-cylinder diesel engine, stable electrical performance, marine-specific cooling, advanced electronic control, and effective sound and vibration management.

The 27MDKDU is a 50 Hz generator designed to operate at 1,500 rpm. This low operating speed supports smooth, durable performance while producing the electrical frequency required by many vessels operating in Europe, Africa, Asia, Australia, the Middle East, and other markets using 50 Hz power systems. Cummins lists the MDKDU within its 22.5–29kW marine generator family, which uses a four-cylinder, four-stroke, water-cooled marine diesel engine and an Onan four-pole alternator.

With 27kW of marine electrical output, the generator can support a wide range of onboard systems when correctly matched to the vessel’s electrical demand. Typical loads may include marine air-conditioning, refrigeration, battery chargers, navigation electronics, lighting, water pumps, communication equipment, galley appliances, entertainment systems, water makers, and other essential hotel loads.

Marine buyers choose the Cummins Onan 27MDKDU-8257A because it offers more than basic generator output. Its digital control, electronic frequency regulation, brushless alternator, marine heat-exchanger cooling, diagnostic protection, vibration isolation, and available sound enclosure help create a dependable onboard power solution for both recreational and commercial use.

Whether required for a new vessel, an onboard electrical upgrade, or a marine generator replacement project, the Cummins Onan Marine QD 27MDKDU-8257A provides the engineering quality, serviceability, and international support expected from a leading marine power manufacturer.

Key Features at a Glance

• 27kW marine diesel generator
• Genuine Cummins Onan Quiet Diesel model
• Designed for 50 Hz marine electrical systems
• Rated operating speed of 1,500 rpm
• Four-cylinder V3300 diesel engine
• Four-stroke, water-cooled engine design
• Brushless four-pole Onan alternator
• Advanced digital electronic control
• Electronic frequency regulation
• Integral voltage regulation
• Freshwater cooling with marine heat exchanger
• Gear-driven raw-water pump
• Water-cooled exhaust mixing elbow
• Optimized vibration-isolated mounting
• Available marine sound shield
• Remote monitoring options
• Worldwide Cummins distributor and service support
• Suitable for new installations and repower projects

Designed for Recreational and Commercial Vessels

The Cummins Onan Marine QD 27MDKDU generator is designed for vessels that require reliable AC power while underway, at anchor, in port without shore power, or during extended offshore operation.

Suitable applications include:

• Motor yachts
• Luxury yachts
• Sportfishing vessels
• Charter boats
• Passenger vessels
• Commercial workboats
• Patrol vessels
• Crew-transfer boats
• Research vessels
• Expedition vessels
• Offshore-support craft
• Liveaboard boats
• Custom boat-building projects
• Marine generator replacements
• Vessel electrical-system upgrades

The generator is particularly appropriate for vessels operating with 50 Hz electrical systems. Before purchase, the exact voltage, phase, amperage, winding configuration, starting voltage, cooling arrangement, and included options associated with specification code 8257A should be verified from the generator nameplate or factory build documentation.

Unlike land-based generator sets, the MDKDU is designed around marine installation requirements. Its cooling, exhaust, mounting, electrical protection, service connections, and corrosion-conscious construction are intended for operation inside a vessel’s machinery space.

Cummins Onan Quiet Diesel Technology

The Cummins Onan Quiet Diesel platform is designed to reduce the noise and vibration commonly associated with onboard diesel generation.

An optimized mounting system helps isolate engine and alternator vibration from the vessel structure. This can reduce the transmission of mechanical vibration into cabins, decks, bulkheads, and living areas. Cummins specifically identifies the optimized mounting system as a major feature of the 22.5/27/29kW generator range.

Quiet Diesel engineering may include:

• Vibration-isolated generator mounts
• Optimized engine and alternator mounting
• Air-intake silencing
• Controlled engine speed
• Balanced rotating components
• Available marine sound enclosure
• Water-cooled exhaust arrangement
• Digital governing for smoother operation

Cummins documentation lists a sound level of approximately 65 dB(A) at one metre for the 27MDKDU when equipped with its sound shield, under the stated measurement conditions. Actual perceived noise will depend on installation quality, machinery-space insulation, exhaust design, ventilation, vessel construction, operating load, and measurement location.

This sound-conscious design makes the generator suitable for yachts, charter vessels, liveaboard boats, and passenger craft where onboard comfort is an important purchasing consideration.

Four-Cylinder V3300 Diesel Engine

The Cummins Onan 27MDKDU is powered by a V3300 four-cylinder diesel engine.

The engine is a four-stroke, indirect-injection, water-cooled diesel designed to operate at 1,500 rpm in the 50 Hz MDKDU configuration. It has a displacement of approximately 3.318 litres, a 98 mm bore, and a 110 mm stroke.

Important engine characteristics include:

• Four-cylinder configuration
• Four-stroke diesel operation
• Indirect fuel injection
• Water-cooled construction
• 3.318-litre displacement
• 98 mm cylinder bore
• 110 mm piston stroke
• 1,500 rpm rated operating speed
• Digital electronic control
• Automatic starting support
• Full-flow lubrication filtration
• Marine heat-exchanger cooling

The engine’s relatively low operating speed contributes to smooth operation and long-term durability. Rather than operating at the higher speeds often found in compact portable generators, the 27MDKDU combines a 1,500 rpm engine with a four-pole alternator to produce 50 Hz electricity.

This arrangement is well suited to vessels requiring consistent electrical power over extended operating periods.

Stable Electrical Output for Modern Vessel Systems

Modern boats rely on sensitive electrical and electronic equipment. Navigation displays, digital controls, communication equipment, chargers, computers, galley appliances, and entertainment systems can be affected by unstable voltage or frequency.

The Cummins Onan 27MDKDU is designed to provide stable marine electrical power using:

• Electronic frequency control
• Digital electronic governing
• Integral voltage regulation
• Brushless alternator construction
• Four-pole alternator design
• Rotating-field architecture
• Protected electrical components
• Mainline circuit protection

Cummins highlights electronic frequency control as an important feature for digital appliances and computers that require quality power.

The alternator uses a single-bearing, four-pole, rotating-field, brushless design. Brushless construction reduces the need for brush inspection or replacement and supports dependable long-term operation.

The generator’s exact output voltage and phase depend on the selected factory winding and specification. Buyers should therefore confirm that 27MDKDU-8257A matches the vessel’s distribution system before purchase.

Advanced Digital Control and Monitoring

The generator uses an advanced digital control system for starting, operation, protection, and diagnostics.

Depending on the installed configuration, operators may access generator information through the local control panel, a basic remote panel, the optional Cummins Onan Digital Display, or a compatible vessel-monitoring network.

The Cummins Onan Digital Display can provide operating and diagnostic information such as:

• AC output voltage
• AC frequency
• Engine coolant temperature
• Engine oil pressure
• Starting-battery voltage
• Total generator operating hours
• Generator load indication
• Engine speed
• Pre-alarm information
• Shutdown-fault information

The manufacturer’s operating documentation also notes that compatible vessel-monitoring systems may communicate through protocols such as SAE J1939, SmartCraft, or NMEA 2000, depending on the generator configuration and installed interfaces.

These monitoring capabilities help operators identify operating conditions and respond to potential issues before they develop into more serious problems.

Generator Protection Features

Marine generators must protect themselves from unsafe operating conditions that can damage the engine, alternator, or connected equipment.

Depending on the exact factory configuration, the 27MDKDU control system may provide monitoring or shutdown protection for conditions such as:

• High engine-coolant temperature
• Low lubricating-oil pressure
• High exhaust temperature
• Loss of raw-water flow
• Low coolant level when the optional sensor is installed
• Overcrank
• Overspeed
• Abnormal AC voltage
• Abnormal frequency
• External emergency shutdown
• Controller or sensor faults

The generator also includes an AC line circuit breaker that helps protect connected conductors against overloads and short circuits originating in the connected equipment.

A qualified marine technician should investigate and correct the cause of any shutdown rather than repeatedly resetting the generator.

Freshwater Cooling and Raw-Water Heat Exchanger

The Cummins Onan 27MDKDU uses a closed freshwater cooling system combined with a marine heat exchanger.

Inside the closed circuit, engine coolant circulates through the diesel engine and carries heat to the heat exchanger. Raw water drawn from outside the vessel passes through the heat exchanger and removes heat from the engine coolant before being discharged through the exhaust or another approved outlet arrangement.

The cooling system generally includes:

• Closed freshwater coolant circuit
• Marine heat exchanger
• Expansion tank
• Coolant-recovery system
• Raw-water pump
• Raw-water hoses and connections
• Thermostat-controlled engine temperature
• Water-cooled exhaust mixing elbow
• Raw-water-flow monitoring

This configuration helps prevent raw seawater from circulating directly through the engine’s internal cooling passages.

Cummins documentation lists an approximate cooling-system capacity of 14 litres for the 27MDKDU family. It also identifies a 76.5°C thermostat opening temperature and approximately 90°C full-opening temperature under the documented configuration.

Cooling capacity and installation requirements should be checked against the current technical documentation for the exact generator.

Marine Exhaust System

The standard marine configuration uses a water-cooled exhaust mixing elbow.

Raw cooling water is introduced into the exhaust downstream from the engine, helping reduce exhaust-gas temperature before the mixture is routed through approved marine exhaust hose, a muffler, water separator, or other correctly engineered exhaust components.

A complete exhaust system may require:

• Water-cooled mixing elbow
• Approved wet-exhaust hose
• Marine waterlift muffler
• Exhaust water separator
• Siphon-break assembly
• Properly positioned overboard outlet
• Adequate exhaust rise
• Correct hose diameter
• Suitable clamps and supports

Poorly designed marine exhaust systems can allow water to flow back toward the engine. The installation should therefore be designed and approved by a qualified marine engineer or generator installer.

Performance and Fuel Consumption

The 27MDKDU is designed to provide efficient diesel operation across changing vessel loads.

Cummins documentation lists the following approximate fuel-consumption figures for the 27MDKDU at 50 Hz:

• No load: approximately 1.9 litres per hour
• Half load: approximately 4.5 litres per hour
• Full load: approximately 9.1 litres per hour

These figures are manufacturer reference values and may vary with generator condition, fuel quality, installation, ambient temperature, maintenance, altitude, exhaust restriction, and actual electrical demand.

Running a generator close to its properly calculated operating range can provide more efficient engine loading than consistently operating a significantly oversized unit at very low load.

A marine electrician should complete a load analysis that considers:

• Continuous electrical loads
• Simultaneous equipment use
• Motor-starting current
• Air-conditioning compressor startup
• Battery-charger demand
• Future equipment upgrades
• Required reserve capacity

Standard Equipment

The exact equipment supplied with the 27MDKDU-8257A should be confirmed from the factory build sheet. Typical equipment for this generator family may include:

• V3300 four-cylinder marine diesel engine
• Brushless four-pole Onan alternator
• Advanced digital electronic controller
• Electronic governor
• Integral voltage regulator
• Electric starter
• Automatic engine preheat
• Electric fuel-transfer pump
• Fuel filter
• Full-flow engine-oil filter
• Freshwater cooling system
• Marine heat exchanger
• Raw-water pump
• Coolant expansion and recovery system
• Water-cooled exhaust mixing elbow
• AC mainline circuit breaker
• Running-time meter
• Vibration-isolated mounting system
• Oil-drain extension
• Fluid-containment base
• Remote-control connection
• Single-point lifting provision
• Operation and installation documentation

Individual units may differ according to build date, regional certification, voltage, phase, starting system, cooling configuration, sound-shield option, and ordered accessories.

Optional Equipment and Accessories

Depending on the factory configuration and vessel requirements, available equipment may include:

• Cummins Onan Digital Display
• Remote start-and-stop panel
• Additional remote control station
• Remote wiring harness
• NMEA 2000 communication interface
• SAE J1939 communication interface
• SmartCraft-compatible monitoring
• Low-coolant-level sensor
• 12V or 24V starting configuration
• Isolated-ground configuration
• Alternative voltage windings
• Single-phase or three-phase configuration
• Sound-shield enclosure
• Keel-cooling conversion
• Dry-exhaust configuration
• Remote fuel-water separator
• Marine muffler
• Exhaust water separator
• Siphon-break kit
• Starting battery
• Genuine maintenance kit
• Fuel filters
• Oil filters
• Raw-water-pump impellers
• Zinc anodes
• Replacement drive belts

Accessory compatibility should be checked against the complete model and specification code.

Ideal Marine Generator Replacement Solution

The Cummins Onan Marine QD 27MDKDU-8257A can be considered when replacing an older marine generator that has become unreliable, inefficient, difficult to service, or inadequate for the vessel’s electrical requirements.

Common reasons for replacement include:

• Unstable AC voltage
• Fluctuating frequency
• Excessive vibration
• Increasing operating noise
• Frequent overheating
• Difficult starting
• Repeated coolant or oil leaks
• High fuel consumption
• Expensive repairs
• Obsolete control equipment
• Poor replacement-parts availability
• Insufficient output for new onboard systems

Before using the 27MDKDU as a replacement, installers should compare:

• Rated power output
• Frequency
• Voltage
• Number of phases
• Starting voltage
• Physical dimensions
• Dry and operating weight
• Mounting locations
• Service clearances
• Fuel supply and return
• Raw-water connections
• Exhaust routing
• Ventilation requirements
• AC cable size
• Circuit protection
• Remote-panel wiring

The replacement should not be selected solely because its kilowatt output is similar to the previous generator.

Reliability and Serviceability

The Cummins Onan 27MDKDU is designed to support practical routine maintenance in marine machinery spaces.

Service-oriented features may include:

• Accessible oil filter
• Replaceable fuel filter
• Oil-drain hose extension
• Coolant-recovery bottle
• Accessible raw-water pump
• Running-time meter
• Digital fault diagnostics
• Remote-control connection
• Bulkhead-style service connections
• Single-point lifting provision
• Fluid-containment base
• Maintenance-free alternator bearings

Cummins offers genuine Onan maintenance parts designed for the applicable generator specifications. The manufacturer states that genuine parts are produced to support generator output and operating life.

Routine maintenance should follow the applicable Cummins Onan manual and may include:

• Checking engine oil
• Checking coolant level
• Inspecting for leaks
• Inspecting raw-water flow
• Cleaning the seawater strainer
• Checking exhaust hoses
• Replacing fuel and oil filters
• Inspecting the raw-water impeller
• Checking belts
• Inspecting battery terminals
• Testing safety shutdowns
• Inspecting vibration mounts
• Checking zinc protection
• Inspecting electrical connections

Cummins recommends checking oil, coolant, leaks, raw-water supply, exhaust condition, battery connections, and related safety items before operation or at the intervals stated in the applicable maintenance schedule.

Why Choose the Cummins Onan 27MDKDU-8257A?

The Cummins Onan Marine QD 27MDKDU-8257A offers a strong combination of output, low-speed diesel operation, stable electrical performance, monitoring capability, marine cooling, and worldwide service support.

Important reasons to consider this model include:

• 27kW output for demanding onboard loads
• 50 Hz operation for compatible marine systems
• Durable 1,500 rpm engine speed
• Proven four-cylinder V3300 diesel engine
• Brushless four-pole alternator
• Electronic frequency control
• Advanced generator diagnostics
• Marine heat-exchanger cooling
• Water-cooled exhaust
• Reduced vibration
• Available sound enclosure
• Remote monitoring options
• Suitable for new builds and replacement projects
• Extensive international Cummins support network

Cummins identifies its certified distributor and dealer network as one of the major benefits supporting the Onan Marine QD range.

Technical Specifications

Cummins notes that dimensions can vary according to the selected configuration. The exact voltage, phase, amperage, enclosure, starting voltage, cooling arrangement, and included options must be confirmed from the generator’s nameplate and factory documentation.

Compatible Products and Installation Accessories

A complete installation may require:

• Starting battery
• Marine battery cables
• Battery isolator
• Remote control panel
• Digital generator display
• Vessel-monitoring interface
• Primary fuel-water separator
• Fuel supply and return hoses
• Raw-water seacock
• Raw-water strainer
• Siphon-break assembly
• Marine wet-exhaust hose
• Waterlift muffler
• Exhaust water separator
• Cooling-water hoses
• AC distribution panel
• Main circuit protection
• Shore-power transfer equipment
• Vessel bonding connection
• Ventilation equipment
• Sound and heat insulation
• Genuine maintenance filters
• Raw-water impeller kits
• Zinc anodes
• Recommended lubricants and coolant

All installation equipment should be selected according to the vessel, generator build specification, applicable marine standards, and local electrical requirements.

Worldwide Supply

Coastal Wave Marine supplies Cummins Onan marine diesel generators to yacht owners, boat builders, marine engineers, shipyards, commercial operators, fleet owners, and international equipment buyers.

Support may include:

• Product identification
• Specification review
• Electrical-configuration confirmation
• New installation enquiries
• Repower and replacement enquiries
• Accessory selection
• Shipping preparation
• Export documentation
• International freight coordination
• Technical product information

Before shipping, buyers should confirm the exact generator model, serial number, specification code, voltage, phase, frequency, starting voltage, cooling arrangement, sound-shield configuration, exhaust components, remote-control equipment, and accessories.

Worldwide delivery availability depends on the destination, freight method, customs requirements, generator dimensions, weight, and applicable import regulations.

Frequently Asked Questions

What is the power output of the Cummins Onan 27MDKDU-8257A?

The generator is rated at 27kW within the Cummins Onan Marine QD range.

Is the Cummins Onan 27MDKDU a 50 Hz generator?

Yes. The MDKDU is the 27kW, 50 Hz model in this generator family and operates at 1,500 rpm.

Which engine powers the 27MDKDU?

It uses a four-cylinder V3300 marine diesel engine with approximately 3.318 litres of displacement.

Is the generator single-phase or three-phase?

The model family can be supplied in different electrical configurations. The exact phase and voltage associated with specification 8257A must be confirmed from the factory build sheet or nameplate.

Does the generator include a sound shield?

A sound-shield configuration is available, but its inclusion on the offered unit must be confirmed.

How loud is the Cummins Onan 27MDKDU?

Cummins documentation lists approximately 65 dB(A) at one metre for the generator with its sound shield under the stated test conditions. Installation design can significantly affect actual onboard sound.

What is the approximate fuel consumption?

Cummins documentation lists approximately 1.9 litres per hour at no load, 4.5 litres per hour at half load, and 9.1 litres per hour at full load.

Can this generator power marine air conditioning?

Yes, provided the complete starting and running demand of the air-conditioning equipment and other connected loads remains within the generator’s capacity.

Does the 27MDKDU support remote monitoring?

Remote panels and digital monitoring options may be available. Compatible data interfaces can include SAE J1939, SmartCraft, or NMEA 2000, depending on configuration.

What cooling system does it use?

It normally uses closed freshwater engine cooling with a marine heat exchanger and raw-water circuit.

Can the 27MDKDU replace an older marine generator?

Yes, when its power output, voltage, phase, dimensions, mounting, cooling, exhaust, fuel, and electrical requirements are compatible with the vessel.

Is worldwide shipping available?

Coastal Wave Marine can assist with international shipping enquiries, subject to destination, freight arrangements, customs procedures, and local import requirements.

Request a Quote

The Cummins Onan Marine QD 27MDKDU-8257A is a dependable 27kW marine generator for buyers who require stable 50 Hz onboard power, durable low-speed diesel operation, advanced monitoring, reduced vibration, and recognized Cummins Onan support.

Contact Coastal Wave Marine to request current availability, confirm the exact 8257A electrical configuration, review included equipment, select compatible installation accessories, discuss worldwide shipping, and obtain a quotation for the Cummins Onan Marine QD 27MDKDU-8257A.