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Sulzer

12RTA84T-D

Name: Sulzer 12RTA84T-D
Brand: Sulzer
SKU: OSE-38712

The Sulzer 12RTA84T-D is a low‑speed, two‑stroke main engine delivering 54 240 kW at 76 rpm, designed for direct‑drive propulsion on large ocean-going vessels.

54240.0 kW

Power

Engine Specifications

Cylinders

840 mm

Bore

3150 mm

Stroke

54,240 kW

MCR Power

76.0 rpm

MCR RPM

2-stroke

Stroke Type

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

Inspector Detail ✓ verified

▸

Designation decoded

Sulzer 12RTA84T-D – 12-cylinder in-line two-stroke crosshead diesel engine, bore 840 mm, stroke 3,150 mm (extended stroke!), gear-driven camshaft, T-D series (Tanker Development/Further Development). Extremely extended stroke with S/B ratio 3.75 – extreme long-stroke design for maximum efficiency at lowest speed.

Background

The RTA84T-D represents a significant further development with drastically extended stroke (3,150 mm vs. 2,400 mm of the standard variant). The S/B ratio of 3.75 is exceptionally high and targets maximum thermodynamic efficiency at very low speed – optimised for direct-drive large tankers with large, slowly rotating propellers. The extended stroke means considerably greater piston rod travel, higher crosshead load and altered vibration characteristics. The overall engine height is significantly greater than the standard variant. Gear-driven camshaft, VIT, Pulse lubrication system, CLU concept. Particular attention required to the longer piston rod and its guidance elements.

Calculated metrics

Stroke To Bore Ratio

3.75

Inspector checklist

Logbook reference values

Parameter	Expected	Deviation means
Maximaler Zünddruck (Pmax)	130–148 bar (lastabhängig, angepasste Steuerzeiten für Langhub)	At extreme S/B ratio 3.75, pressure curves may differ from standard stroke. Deviation >5 bar between cylinders: check VIT, nozzles or compression.
Exhaust gas temperature per cylinder	320–380 °C at optimum tanker load	Long-stroke design tends toward lower exhaust temperatures due to better expansion. Individual cylinder deviation >25 °C: fuel injection or valve problem.
Kühlwassertemperatur Laufbuchse	75–85 °C Eintritt / max. 95 °C Austritt	Längere Laufbuchse hat größere Wärmeabgabefläche – Temperaturverteilung über die Laufbuchsenlänge beachten. Hotspots können auf lokale Kühlungsdefizite hinweisen.
Kreuzkopf-Lagertemperatur	<65 °C (particularly critical with extended stroke)	Elevated temperature indicates lubrication shortage or bearing wear. At 3150 mm stroke, higher load due to longer lever arm – check oil supply and oil quality.
Zylinderschmieröl-Verbrauch	0,9–1,4 g/kWh	With extended liner, altered consumption pattern may occur. Perform scrapdown analysis to assess neutralization capacity and wear metals.
Kurbelwellen-Deflexion	±0,05 mm (Herstellerangabe für T-D beachten)	Due to greater engine height, altered center of gravity – perform deflection measurement at defined loading condition. Foundation stability particularly critical for long-stroke engine.
Schwingungsdämpfer-Temperatur/Ölstand	Gemäß Herstellerangabe (typisch <70 °C Öltemperatur)	Elevated temperature or oil level loss: damper efficiency reduced – immediate inspection required. Long-stroke engine exhibits different vibration natural frequencies.
Kolbenstangen-Stopfbuchse Leckage	Minimale Leckage, Ölsammelbehälter < 50 ml/h pro Zylinder	Elevated leakage: stuffing box rings worn or piston rod surface damaged. With extended piston rod, additionally check guide rings.

Common Failure Modes

Crosshead guide wear due to extended stroke

Symptoms: ['Knocking noise at top dead center reversal', 'Erhöhte Kreuzkopf-Lagertemperatur', 'Uneven wear of guide surfaces', 'Kolbenstangenauslenkung']

Causes: Higher lateral forces due to extended stroke, Unzureichende Schmierung der Führungsbahnen, Fehlausrichtung der Kolbenstange, Material fatigue at high operating hours

Preventive: Measure crosshead clearance at every dock call. Assess guide surface condition visually and metrologically. Monitor lubrication oil supply for pressure and flow. Check piston rod straightness during CLU overhaul.

Torsional vibration problem in long-stroke configuration

Symptoms: ['Unusual vibrations at certain speeds', 'Schäden an Kupplungselementen', 'Camshaft gear wear', 'Wellenleitung-Probleme']

Causes: Altered natural frequencies due to extreme S/B ratio, Unzureichende Torsionsdämpfer-Kapazität, Resonanz in verbotenen Drehzahlbereichen

Preventive: Cross-check torsional vibration report against actual operating data. Strictly observe prohibited speed ranges. Regularly inspect torsion damper and check silicone oil condition.

Kolbenstangen-Stopfbuchsen-Versagen

Symptoms: ['Erhöhter Ölverbrauch im Kurbelgehäuse', 'Ölnebel im Spülluftkasten', 'Stopfbuchsen-Leckage sichtbar', 'Gasaustritt aus Stopfbuchse']

Causes: Verlängerte Kolbenstange mit größerer thermischer Ausdehnung, Oberflächenschäden an der Kolbenstange, Ring wear due to higher piston speed in long-stroke

Preventive: Systematically renew stuffing box rings during CLU overhaul. Check piston rod surface for scoring and corrosion. Monitor strip efficiency through oil consumption monitoring.

Liner deformation due to thermal stress

Symptoms: ['Uneven piston ring wear', 'Blow-by-Zunahme', 'Erhöhte Laufbuchsentemperatur-Gradienten']

Causes: Längere Laufbuchse anfälliger für thermische Verformung, Ungleichmäßige Kühlwasserverteilung über die Laufbuchsenlänge, Kalkablagerungen im Kühlmantel

Preventive: Internal liner measurement at every CLU overhaul (ovality and conicity over full length). Strictly control cooling water treatment. Rebore or replace liner if necessary.

Expert tips

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Related components

C r o s s h e a d g u i d e b a r s , e x t e n d e d p i s t o n r o d , c o n n e c t i n g r o d a n d b e a r i n g , t o r s i o n a l v i b r a t i o n d a m p e r , a x i a l v i b r a t i o n d a m p e r , c r a n k s h a f t b e a r i n g , t h r u s t b e a r i n g , c a m s h a f t g e a r t r a i n , t u r b o c h a r g e r , f o u n d a t i o n ( n o t e e l e v a t e d e n g i n e h e i g h t ) , s h a f t l i n e a l i g n m e n t , p i s t o n r o d s t u f f i n g b o x , s c a v e n g e a i r b o x f i r e p r o t e c t i o n

Classification & regulatory

Torsional vibration report must be on board and prohibited speed ranges marked at the bridge (IACS UR M68). For long-stroke engine with altered vibration characteristics, special attention to shaft line torsional report per classification society. MARPOL Annex VI NOx compliance and EEXI assessment. For tanker operation observe CAS and Enhanced Survey Programme (ESP).

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

Other Cylinder Configurations 50

Components & Design

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Technical Data

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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 #38712 · ✓ still in production