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Sulzer

6RTA72U

Name: Sulzer 6RTA72U
Brand: Sulzer
SKU: OSE-38647

The Sulzer 6RTA72U is a low‑speed, two‑stroke marine diesel engine delivering 20.4 MW at 91 rpm, known for its robust camshaft design and constant‑pressure turbocharging.

20400.0 kW

Power

Engine Specifications

Cylinders

720 mm

Bore

2500 mm

Stroke

20,400 kW

MCR Power

91.0 rpm

MCR RPM

2-stroke

Stroke Type

Family: Sulzer RTA · Tier: IMO Tier I · Fuel: HFO, MDO

Inspector Detail ✓ verified

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Designation decoded

Sulzer RTA72U – 6-Zylinder-Zweitakt-Kreuzkopfmotor mit zahnradgetriebenem Nockenwellen-Ventiltrieb, 720 mm Bohrung, 2500 mm Hub. U=Ultra-Langhub-Ausführung. Obwohl der Standardhub bereits 2500 mm beträgt, kennzeichnet das U-Suffix eine drehzahloptimierte Variante für maximale Propellereffizienz.

Background

The RTA72U is the ultra-long-stroke variant of the RTA72 engine series. With identical stroke of 2500 mm as the standard version, the U variant is designed for a lower rated speed, which permits the use of larger propellers with higher efficiency. The engine features adjusted valve timing, modified turbocharger arrangement and optimized VIT characteristic. Pulse Lubrication and CLU are standard. The lower speed reduces mean piston speed and wear, however increases torque loading on the running gear.

Calculated metrics

Stroke To Bore Ratio

3.47

Mean Effective Pressure Bar

19.2

Inspector checklist

Camshaft and drive gears

Inspect gear flanks for wear and fatigue cracks – elevated torque load at U variant
Nockenwellenlager-Spiel messen
Examine cam profiles for wear
Check drive gear fastening and dowel pins

Cylinder liners and piston rings

Laufbuchsen-Verschleißmessung durchführen
Kolbenring-Stoßspiel messen
CLU-Schmiernuten auf Durchgängigkeit prüfen
Assess running surface condition – different wear patterns possible at lower speed

VIT system and fuel injection

VIT-Kurve der U-Variante prüfen – unterscheidet sich von Standardversion
Check fuel injection nozzle opening pressure and spray pattern
Inspect fuel pump plunger for wear
Verify fuel injection timing at rated speed

Crosshead and running gear

Crosshead bearing clearance – pay attention to elevated torque loading at U variant
Pleuelstangen-Schrauben auf Vorspannung prüfen
Kolbenstangen-Stopfbuchse kontrollieren
Measure main bearing condition and clearance

Turboladerzuordnung

Check turbocharger operating points at U speed
Compare charge pressure and turbocharger speed with U reference values
Pay attention to turbocharger surge limit at part load
Ladeluftkühler-Druckverlust messen

Logbook reference values

Parameter	Expected	Deviation means
Exhaust gas temperature per cylinder	325–385 °C at 85 % MCR	Elevated values indicate fuel injection or turbocharger problems
Cylinder liner wear	0,04–0,09 mm/1000 Bh	U variant typically shows slightly lower wear rates due to reduced piston speed
Spülluftdruck	2.8–3.4 bar at MCR	Abweichungen beeinflussen Spüleffizienz – Turboladerzuordnung der U-Variante beachten
Spitzendruck (Pmax)	Gemäß U-Testprotokoll, typisch 148–162 bar	Bei U-Variante höhere Spitzendrücke möglich – Abweichungen zwischen Zylindern >5 bar untersuchen
Kurbelwellendurchbiegung	Gemäß Herstellergrenzwerte, typisch max. 1/100 mm pro Messposition	Increased deflection in U-variant more critical due to higher torque – check main bearing wear
Hauptlager-Temperatur	60–72 °C	Elevated temperatures in U-variant particularly critical due to higher torque loading

Common Failure Modes

Hauptlager-Überlastung

Symptoms: ['Erhöhte Lagertemperaturen', 'Veränderte Kurbelwellendurchbiegung', 'Bearing shell wear in lower area']

Causes: Higher torque at U-speed overloads bearings, Oil film failure at low speed, Fundamentverformung

Preventive: Measure crankshaft deflection at shorter intervals, continuously monitor bearing temperatures and check foundation bolt preload

Turbocharger surging at part load

Symptoms: ['Pulsierendes Geräusch vom Turbolader', 'Schwankender Ladedruck', 'Leistungsschwankungen']

Causes: U-variant-specific turbocharger characteristic unfavorable at part load, Verschmutzte Turbineneintrittsflächen, Ladeluftkühler-Verschmutzung

Preventive: Check turbocharger operating points regularly, utilize scavenge system and limit part load operation per manufacturer recommendation

Nockenwellen-Antriebszahnrad-Ermüdung

Symptoms: ['Abnormale Geräusche aus dem Steuerungsgehäuse', 'Metallpartikel im Öl', 'Einspritz-Timing-Abweichungen']

Causes: Elevated torque peaks at lower speed, Materialermüdung, Ungenügende Schmierung

Preventive: Check gears at every camshaft inspection with MT/PT, monitor oil analysis

Piston rod stuffing box wear

Symptoms: ['Ölverlust im Spülluftkasten', 'Gasaustritt an Stopfbuchse', 'Erhöhter Ölverbrauch']

Causes: Mechanical stress due to long stroke, Kolbenstangen-Oberflächenverschleiß, Dichtungselement-Verhärtung

Preventive: Replace stuffing box seals regularly and inspect piston rod surface

Expert tips

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Related components

Turbolader (Kennlinie, Surging-Verhalten, Lagerung) Scavenge air cooler (pressure drop and fouling) Exhaust valve spindle and seat Kolbenkühlung (Teleskoprohr-Dichtungen) Main bearing and crankshaft deflection Vibration damper (torsional damper particularly important for U-variant) Shaft line and propeller bearing

Classification & regulatory

IACS UR Z10.5 for machinery survey. U-variant requires U-specific test protocols and performance curves. NOx emissions per MARPOL Annex VI – VIT curve of U-version documented in EIAPP Technical File. Measure crankshaft deflection at every intermediate survey. Torsional vibration calculation for U-speed must be available.

Reference content for inspector orientation. Always verify against manufacturer's manual, latest service letters and class society requirements.

Other Cylinder Configurations 50

Components & Design

Component data being added…

Technical Data

unified from engine model True

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Manuals

operating
Sulzer RTA Operating Manual
Wärtsilä Switzerland (historical Sulzer)
maintenance
Sulzer RTA Maintenance Manual
Wärtsilä Switzerland (historical Sulzer)
spare_parts
Sulzer RTA Spare Parts Catalogue
Wärtsilä Switzerland (historical Sulzer)

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Equipment Model #38647 · ✓ still in production